A light-emitting diode (LED) is a semiconductor diode that emits incoherent narrow-spectrum light when electrically biased in the forward direction of the p-n junction.
See also LED Lamps
A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices, and are increasingly used for lighting. Introduced as a practical electronic component in 1962, early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness.
The LED is based on the semiconductor diode. When a diode is forward biased (switched on), electrons are able to recombine with holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. An LED is usually small in area (less than 1 mm2), and integrated optical components are used to shape its radiation pattern and assist in reflection. LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. However, they are relatively expensive and require more precise current and heat management than traditional light sources. Current LED products for general lighting are more expensive to buy than fluorescent lamp sources of comparable output.
They also enjoy use in applications as diverse as replacements for traditional light sources in automotive lighting (particularly indicators) and in traffic signals. Airbus uses LED lighting in their A320 Enhanced since 2007, and Boeing plans its use in the 787. The compact size of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are useful in advanced communications technology.
Electroluminescence was discovered in 1907 by the British experimenter H. J. Round of Marconi Labs, using a crystal of silicon carbide and a cat's-whisker detector. Russian Oleg Vladimirovich Losev independently reported on the creation of a LED in 1927. His research was distributed in Russian, German and British scientific journals, but no practical use was made of the discovery for several decades. Rubin Braunstein of the Radio Corporation of America reported on infrared emission from gallium arsenide (GaAs) and other semiconductor alloys in 1955. Braunstein observed infrared emission generated by simple diode structures using gallium antimonide (GaSb), GaAs, indium phosphide (InP), and silicon-germanium (SiGe) alloys at room temperature and at 77 kelvins.
In 1961, experimenters Robert Biard and Gary Pittman working at Texas Instruments, found that GaAs emitted infrared radiation when electric current was applied and received the patent for the infrared LED.
The first practical visible-spectrum (red) LED was developed in 1962 by Nick Holonyak Jr., while working at General Electric Company. Holonyak is seen as the "father of the light-emitting diode". M. George Craford, a former graduate student of Holonyak, invented the first yellow LED and improved the brightness of red and red-orange LEDs by a factor of ten in 1972. In 1976, T.P. Pearsall created the first high-brightness, high efficiency LEDs for optical fiber telecommunications by inventing new semiconductor materials specifically adapted to optical fiber transmission wavelengths.
Up to 1968 visible and infrared LEDs were extremely costly, on the order of US $200 per unit, and so had little practical application. The Monsanto Company was the first organization to mass-produce visible LEDs, using gallium arsenide phosphide in 1968 to produce red LEDs suitable for indicators. Hewlett Packard (HP) introduced LEDs in 1968, initially using GaAsP supplied by Monsanto. The technology proved to have major applications for alphanumeric displays and was integrated into HP's early handheld calculators. In the 1970s commercially successful LED devices at under five cents each were produced by Fairchild Optoelectronics. These devices employed compound semiconductor chips fabricated with the planar process invented by Dr. Jean Hoerni at Fairchild Semiconductor. The combination of planar processing for chip fabrication and innovative packaging techniques enabled the team at Fairchild led by optoelectronics pioneer Thomas Brandt to achieve the necessary cost reductions. These techniques continue to be used by LED producers.
The first commercial LEDs were commonly used as replacements for incandescent and neon indicator lamps, and in seven-segment displays, first in expensive equipment such as laboratory and electronics test equipment, then later in such appliances as TVs, radios, telephones, calculators, and even watches signal applications). These red LEDs were bright enough only for use as indicators, as the light output was not enough to illuminate an area. Later, other colors became widely available and also appeared in appliances and equipment. As the LED materials technology became more advanced, the light output was increased, while maintaining the efficiency and the reliability to an acceptable level. The invention and development of the high power white light LED led to use for illumination. Most LEDs were made in the very common 5 mm T1¾ and 3 mm T1 packages, but with increasing power output, it has become increasingly necessary to shed excess heat in order to maintain reliability, so more complex packages have been adapted for efficient heat dissipation. Packages for state-of-the-art high power LEDs bear little resemblance to early LEDs.
The first high-brightness blue LED was demonstrated by Shuji Nakamura of Nichia Corporation and was based on InGaN borrowing on critical developments in GaN nucleation on sapphire substrates and the demonstration of p-type doping of GaN which were developed by Isamu Akasaki and H. Amano in Nagoya. In 1995, Alberto Barbieri at the Cardiff University Laboratory (GB) investigated the efficiency and reliability of high-brightness LEDs and demonstrated a very impressive result by using a transparent contact made of indium tin oxide (ITO) on (AlGaInP/GaAs) LED. The existence of blue LEDs and high efficiency LEDs quickly led to the development of the first white LED, which employed a Y3Al5O12:Ce, or "YAG", phosphor coating to mix yellow (down-converted) light with blue to produce light that appears white. Nakamura was awarded the 2006 Millennium Technology Prize for his invention.
The development of LED technology has caused their efficiency and light output to increase exponentially, with a doubling occurring about every 36 months since the 1960s, in a way similar to Moore's law. The advances are generally attributed to the parallel development of other semiconductor technologies and advances in optics and material science. This trend is normally called Haitz's Law after Dr. Roland Haitz.
In February 2008, Bilkent university in Turkey reported 300 lumens of visible light per watt luminous efficacy (not per electrical watt) and warm light by using nanocrystals .
In January 2009, researchers from Cambridge University reported a process for growing gallium nitride (GaN) LEDs on silicon. Production costs could be reduced by 90% using six-inch silicon wafers instead of two-inch sapphire wafers. The team was led by Colin Humphreys.
Like a normal diode, the LED consists of a chip of semiconducting material doped with impurities to create a p-n junction. As in other diodes, current flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Charge-carriers—electrons and holes—flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon.
The wavelength of the light emitted, and therefore its color, depends on the band gap energy of the materials forming the p-n junction. In silicon or germanium diodes, the electrons and holes recombine by a non-radiative transition which produces no optical emission, because these are indirect band gap materials. The materials used for the LED have a direct band gap with energies corresponding to near-infrared, visible or near-ultraviolet light.
LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have made possible the production of devices with ever-shorter wavelengths, producing light in a variety of colors.
LEDs are usually built on an n-type substrate, with an electrode attached to the p-type layer deposited on its surface. P-type substrates, while less common, occur as well. Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate.
Most materials used for LED production have very high refractive indices. This means that much light will be reflected back in to the material at the material/air surface interface. Therefore Light extraction in LEDs is an important aspect of LED production, subject to much research and development.
Efficiency and operational parameters
Typical indicator LEDs are designed to operate with no more than 30–60 milliwatts [mW] of electrical power. Around 1999, Philips Lumileds introduced power LEDs capable of continuous use at one watt [W]. These LEDs used much larger semiconductor die sizes to handle the large power inputs. Also, the semiconductor dies were mounted onto metal slugs to allow for heat removal from the LED die.
One of the key advantages of LED-based lighting is its high efficiency, as measured by its light output per unit power input. White LEDs quickly matched and overtook the efficiency of standard incandescent lighting systems. In 2002, Lumileds made five-watt LEDs available with a luminous efficacy of 18–22 lumens per watt [lm/W]. For comparison, a conventional 60–100 W incandescent lightbulb produces around 15 lm/W, and standard fluorescent lights produce up to 100 lm/W. A recurring problem is that efficiency will fall dramatically for increased current. This effect is known as droop and effectively limits the light output of a given LED, increasing heating more than light output for increased current.
In September 2003, a new type of blue LED was demonstrated by the company Cree, Inc. to provide 24 mW at 20 milliamperes [mA]. This produced a commercially packaged white light giving 65 lm/W at 20 mA, becoming the brightest white LED commercially available at the time, and more than four times as efficient as standard incandescents. In 2006 they demonstrated a prototype with a record white LED luminous efficacy of 131 lm/W at 20 mA. Also, Seoul Semiconductor has plans for 135 lm/W by 2007 and 145 lm/W by 2008, which would be approaching an order of magnitude improvement over standard incandescents and better even than standard fluorescents. Nichia Corporation has developed a white LED with luminous efficacy of 150 lm/W at a forward current of 20 mA.
It should be noted that high-power (≥ 1 W) LEDs are necessary for practical general lighting applications. Typical operating currents for these devices begin at 350 mA. The highest efficiency high-power white LED is claimed by Philips Lumileds Lighting Co. with a luminous efficacy of 115 lm/W (350 mA)
Note that these efficiencies are for the LED chip only, held at low temperature in a lab. In a lighting application, operating at higher temperature and with drive circuit losses, efficiencies are much lower. United States Department of Energy (DOE) testing of commercial LED lamps designed to replace incandescent lamps or CFLs showed that average efficacy was still about 46 lm/W in 2009 (tested performance ranged from 17 lm/W to 79 lm/W).
Cree issued a press release on November 19, 2008 about a laboratory prototype LED achieving 161 lumens per watt at room temperature. The total output was 173 lumens, and the correlated color temperature was reported to be 4689 K.
Lifetime and failure
Solid state devices such as LEDs are subject to very limited wear and tear if operated at low currents and at low temperatures. Many of the LEDs produced in the 1970s and 1980s are still in service today. Typical lifetimes quoted are 25,000 to 100,000 hours but heat and current settings can extend or shorten this time significantly.
The most common symptom of LED (and diode laser) failure is the gradual lowering of light output and loss of efficiency. Sudden failures, although rare, can occur as well. Early red LEDs were notable for their short lifetime. With the development of high-power LEDs the devices are subjected to higher junction temperatures and higher current densities than traditional devices. This causes stress on the material and may cause early light output degradation. To quantitatively classify lifetime in a standardized manner it has been suggested to use the terms L75 and L50 which is the time it will take a given LED to reach 75% and 50% light output respectively. L50 is equivalent to the half-life of the LED.
Colors and materials
Conventional LEDs are made from a variety of inorganic semiconductor materials, the following table shows the available colors with wavelength range, voltage drop and material:
||λ > 760
||ΔV < 1.9
||Gallium arsenide (GaAs)
Aluminium gallium arsenide (AlGaAs)
||610 < λ < 760
||1.63 < ΔV < 2.03
||Aluminium gallium arsenide (AlGaAs)
Gallium arsenide phosphide (GaAsP)
Aluminium gallium indium phosphide (AlGaInP)
Gallium(III) phosphide (GaP)
||590 < λ < 610
||2.03 < ΔV < 2.10
||Gallium arsenide phosphide (GaAsP)
Aluminium gallium indium phosphide (AlGaInP)
Gallium(III) phosphide (GaP)
||570 < λ < 590
||2.10 < ΔV < 2.18
||Gallium arsenide phosphide (GaAsP)
Aluminium gallium indium phosphide (AlGaInP)
Gallium(III) phosphide (GaP)
||500 < λ < 570
||1.9 < ΔV < 4.0
||Indium gallium nitride (InGaN) / Gallium(III) nitride (GaN)
Gallium(III) phosphide (GaP)
Aluminium gallium indium phosphide (AlGaInP)
Aluminium gallium phosphide (AlGaP)
||450 < λ < 500
||2.48 < ΔV < 3.7
||Zinc selenide (ZnSe)
Indium gallium nitride (InGaN)
Silicon carbide (SiC) as substrate
Silicon (Si) as substrate — (under development)
||400 < λ < 450
||2.76 < ΔV < 4.0
||Indium gallium nitride (InGaN)
||2.48 < ΔV < 3.7
||Dual blue/red LEDs,
blue with red phosphor,
or white with purple plastic
||λ < 400
||3.1 < ΔV < 4.4
||Diamond (235 nm)
Boron nitride (215 nm)
Aluminium nitride (AlN) (210 nm)
Aluminium gallium nitride (AlGaN)
Aluminium gallium indium nitride (AlGaInN) — (down to 210 nm)
||ΔV = 3.5
||Blue/UV diode with yellow phosphor
Ultraviolet and blue LEDs
Blue LEDs are based on the wide band gap semiconductors GaN (gallium nitride) and InGaN (indium gallium nitride). They can be added to existing red and green LEDs to produce the impression of white light, though white LEDs today rarely use this principle.
The first blue LEDs were made in 1971 by Jacques Pankove (inventor of the gallium nitride LED) at RCA Laboratories. These devices had too little light output to be of much practical use. However, early blue LEDs found use in some low-light applications, such as the high-beam indicators for cars. In the late 1980s, key breakthroughs in GaN epitaxial growth and p-type doping ushered in the modern era of GaN-based optoelectronic devices. Building upon this foundation, in 1993 high brightness blue LEDs were demonstrated.
By the late 1990s, blue LEDs had become widely available. They have an active region consisting of one or more InGaN quantum wells sandwiched between thicker layers of GaN, called cladding layers. By varying the relative InN-GaN fraction in the InGaN quantum wells, the light emission can be varied from violet to amber. AlGaN aluminium gallium nitride of varying AlN fraction can be used to manufacture the cladding and quantum well layers for ultraviolet LEDs, but these devices have not yet reached the level of efficiency and technological maturity of the InGaN-GaN blue/green devices. If the active quantum well layers are GaN, as opposed to alloyed InGaN or AlGaN, the device will emit near-ultraviolet light with wavelengths around 350–370 nm. Green LEDs manufactured from the InGaN-GaN system are far more efficient and brighter than green LEDs produced with non-nitride material systems.
With nitrides containing aluminium, most often AlGaN and AlGaInN, even shorter wavelengths are achievable. Ultraviolet LEDs in a range of wavelengths are becoming available on the market. Near-UV emitters at wavelengths around 375–395 nm are already cheap and often encountered, for example, as black light lamp replacements for inspection of anti-counterfeiting UV watermarks in some documents and paper currencies. Shorter wavelength diodes, while substantially more expensive, are commercially available for wavelengths down to 247 nm. As the photosensitivity of microorganisms approximately matches the absorption spectrum of DNA, with a peak at about 260 nm, UV LED emitting at 250–270 nm are to be expected in prospective disinfection and sterilization devices. Recent research has shown that commercially available UVA LEDs (365 nm) are already effective disinfection and sterilization devices.
Deep-UV wavelengths were obtained in laboratories using aluminium nitride (210 nm), boron nitride (215 nm) and diamond (235 nm).
There are two primary ways of producing high intensity white-light using LEDs. One is to use individual LEDs that emit three primary colors—red, green, and blue—and then mix all the colors to produce white light. The other is to use a phosphor material to convert monochromatic light from a blue or UV LED to broad-spectrum white light, much in the same way a fluorescent light bulb works.
Due to metamerism, it is possible to have quite different spectra which appear white.
White light can be produced by mixing differently colored light, the most common method is to use red, green and blue (RGB). Hence the method is called multi-colored white LEDs (sometimes referred to as RGB LEDs). Because its mechanism is involved with sophisticated electro-optical design to control the blending and diffusion of different colors, this approach has rarely been used to mass produce white LEDs in the industry. Nevertheless this method is particularly interesting to many researchers and scientists because of the flexibility of mixing different colors. In principle, this mechanism also has higher quantum efficiency in producing white light.
There are several types of multi-colored white LEDs: di-, tri-, and tetrachromatic white LEDs. Several key factors that play among these different approaches include color stability, color rendering capability, and luminous efficacy. Often higher efficiency will mean lower color rendering, presenting a trade off between the luminous efficiency and color rendering. For example, the dichromatic white LEDs have the best luminous efficacy (120 lm/W), but the lowest color rendering capability. Conversely, although tetrachromatic white LEDs have excellent color rendering capability, they often have poor luminous efficiency. Trichromatic white LEDs are in between, having both good luminous efficacy (>70 lm/W) and fair color rendering capability.
What multi-color LEDs offer is not merely another solution of producing white light, but is a whole new technique of producing light of different colors. In principle, most perceivable colors can be produced by mixing different amounts of three primary colors, and this makes it possible to produce precise dynamic color control as well. As more effort is devoted to investigating this technique, multi-color LEDs should have profound influence on the fundamental method which we use to produce and control light color. However, before this type of LED can truly play a role on the market, several technical problems need to be solved. These certainly include that this type of LED's emission power decays exponentially with increasing temperature, resulting in a substantial change in color stability. Such problems are not acceptable for industrial usage. Therefore, many new package designs aimed at solving this problem have been proposed and their results are now being reproduced by researchers and scientists.
This method involves coating an LED of one color (mostly blue LED made of InGaN) with phosphor of different colors to produce white light, the resultant LEDs are called phosphor-based white LEDs. A fraction of the blue light undergoes the Stokes shift being transformed from shorter wavelengths to longer. Depending on the color of the original LED, phosphors of different colors can be employed. If several phosphor layers of distinct colors are applied, the emitted spectrum is broadened, effectively increasing the color rendering index (CRI) value of a given LED.
Phosphor based LEDs have a lower efficiency than normal LEDs due to the heat loss from the Stokes shift and also other phosphor-related degradation issues. However, the phosphor method is still the most popular technique for manufacturing high intensity white LEDs. The design and production of a light source or light fixture using a monochrome emitter with phosphor conversion is simpler and cheaper than a complex RGB system, and the majority of high intensity white LEDs presently on the market are manufactured using phosphor light conversion.
The greatest barrier to high efficiency is the seemingly unavoidable Stokes energy loss. However, much effort is being spent on optimizing these devices to higher light output and higher operation temperatures. For instance, the efficiency can be increased by adapting better package design or by using a more suitable type of phosphor. Philips Lumileds' patented conformal coating process addresses the issue of varying phosphor thickness, giving the white LEDs a more homogeneous white light. With development ongoing, the efficiency of phosphor based LEDs is generally increased with every new product announcement.
Technically the phosphor based white LEDs encapsulate InGaN blue LEDs inside of a phosphor coated epoxy. A common yellow phosphor material is cerium-doped yttrium aluminium garnet (Ce3+:YAG).
White LEDs can also be made by coating near ultraviolet (NUV) emitting LEDs with a mixture of high efficiency europium-based red and blue emitting phosphors plus green emitting copper and aluminium doped zinc sulfide (ZnS:Cu, Al). This is a method analogous to the way fluorescent lamps work. This method is less efficient than the blue LED with YAG:Ce phosphor, as the Stokes shift is larger and more energy is therefore converted to heat, but yields light with better spectral characteristics, which render color better. Due to the higher radiative output of the ultraviolet LEDs than of the blue ones, both approaches offer comparable brightness. Another concern is that UV light may leak from a malfunctioning light source and cause harm to human eyes or skin.
Other white LEDs
Another method used to produce experimental white light LEDs used no phosphors at all and was based on homoepitaxially grown zinc selenide (ZnSe) on a ZnSe substrate which simultaneously emitted blue light from its active region and yellow light from the substrate.
Organic light-emitting diodes (OLEDs)
If the emitting layer material of the LED is an organic compound, it is known as an organic light emitting diode (OLED). To function as a semiconductor, the organic emitting material must have conjugated pi bonds. The emitting material can be a small organic molecule in a crystalline phase, or a polymer. Polymer materials can be flexible; such LEDs are known as PLEDs or FLEDs.
Compared with regular LEDs, OLEDs are lighter, and polymer LEDs can have the added benefit of being flexible. Some possible future applications of OLEDs could be:
- Inexpensive, flexible displays
- Light sources
- Wall decorations
- Luminous cloth
OLEDs have been used to produce visual displays for portable electronic devices such as cellphones, digital cameras, and MP3 players. Larger displays have been demonstrated, but their life expectancy is still far too short (<1,000 hours) to be practical.
Today, OLEDs operate at substantially lower efficiency than inorganic (crystalline) LEDs.
Quantum dot LEDs (experimental)
A new technique developed by Michael Bowers, a graduate student at Vanderbilt University in Nashville, involves coating a blue LED with quantum dots that glow white in response to the blue light from the LED. This technique produces a warm, yellowish-white light similar to that produced by incandescent bulbs.
Quantum dots are semiconductor nanocrystals that possess unique optical properties. Their emission color can be tuned from the visible throughout the infrared spectrum. This allows quantum dot LEDs to create almost any color on the CIE diagram. This provides more color options and better color rendering white LEDs. Quantum dot LEDs are available in the same package types as traditional phosphor based LEDs.
In September 2009 Nanoco Group announced that it has signed a joint development agreement with a major Japanese electronics company under which it will design and develop quantum dots for use in light emitting diodes (LEDs) in liquid crystal display (LCD) televisions.
The main types of LEDs are miniature, high power devices and custom designs such as alphanumeric or multi-color.
These are mostly single-die LEDs used as indicators, and they come in various-sizes from 2 mm to 8 mm, through-hole and surface mount packages. They are usually simple in design, not requiring any separate cooling body. Typical current ratings ranges from around 1 mA to above 20 mA. The small scale sets a natural upper boundary on power consumption due to heat caused by the high current density and need for heat sinking.
High power LEDs
High power LEDs (HPLED) can be driven at currents from hundreds of mA to more than an ampere, compared with the tens of mA for other LEDs. Some can produce over a thousand lumens. Since overheating is destructive, the HPLEDs must be mounted on a heat sink to allow for heat dissipation. If the heat from a HPLED is not removed, the device will burn out in seconds. A single HPLED can often replace an incandescent bulb in a flashlight, or be set in an array to form a powerful LED lamp.
Some well-known HPLEDs in this category are the Lumileds Rebel Led, Osram Opto Semiconductors Golden Dragon and Cree X-lamp. As of September 2009 some HPLEDs manufactured by Cree Inc. now exceed 105 lm/W (e.g. the XLamp XP-G LED chip emitting Cool White light) and are being sold in lamps intended to replace incandescent, halogen, and even fluorescent style lights as LEDs become more cost competitive.
LEDs have been developed by Seoul Semiconductor that can operate on AC power without the need for a DC converter. For each half cycle part of the LED emits light and part is dark, and this is reversed during the next half cycle. The efficacy of this type of HPLED is typically 40 lm/W. A large number of LED elements in series may be able to operate directly from line voltage. In 2009 Seoul Semiconductor released a high DC voltage capable of being driven from AC power with a simple controlling circuit. The low power dissipation of these LED afford them to be use used more flexibly than the original AC LED.
Superflux is the trademarked name for a series of medium power through-hole mounted LEDs of a particular shape manufactured by Lumileds. They consist of a square package, with the internal diode mounted to four leads (two cathode leads, two anode leads) for better heat conduction and an integrated dome lens. This package is now often called a Piranha package, since the Superflux name is trademarked. The most common use of these LEDs are light panels, emergency lighting and automotive LED tail-light lighting (though they have recently been superseded by SnapLEDs in many automotive applications). These wide angle LEDs provide large areas of light and a wide viewing angle in a small compact diode. Additionally, due to the larger amount of metal in the LED, they are able to handle higher currents (up to 70mA). The higher current allows for the much higher light output required for tail-lights and emergency lighting.
- Flashing LEDs are used as attention seeking indicators without requiring external electronics. Flashing LEDs resemble standard LEDs but they contain an integrated multivibrator circuit which causes the LED to flash with a typical period of one second. In diffused lens LEDs this is visible as a small black dot. Most flashing LEDs emit light of a single color, but more sophisticated devices can flash between multiple colors and even fade through a color sequence using RGB color mixing.
- Bi-color LEDs are actually two different LEDs in one case. They consist of two dies connected to the same two leads antiparallel to each other. Current flow in one direction produces one color, and current in the opposite direction produces the other color. Alternating the two colors with sufficient frequency causes the appearance of a blended third color. For example, a red/green LED operated in this fashion will color blend to produce a yellow appearance.
- Tri-color LEDs are two LEDs in one case, but the two LEDs are connected to separate leads so that the two LEDs can be controlled independently and lit simultaneously. A three-lead arrangement is typical with one common lead (anode or cathode).
- RGB LEDs contain red, green and blue emitters, generally using a four-wire connection with one common lead (anode or cathode). These LEDs can have either common positive or common negative leads. Others however, have only two leads (positive and negative) and have a built in tiny electronic control unit.
- Alphanumeric LED displays are available in seven-segment and starburst format. Seven-segment displays handle all numbers and a limited set of letters. Starburst displays can display all letters. Seven-segment LED displays were in widespread use in the 1970s and 1980s, but increasing use of liquid crystal displays, with their lower power consumption and greater display flexibility, has reduced the popularity of numeric and alphanumeric LED displays.
Considerations for use
The current/voltage characteristic of an LED is similar to other diodes, in that the current is dependent exponentially on the voltage. This means that a small change in voltage can lead to a large change in current. If the maximum voltage rating is exceeded by a small amount the current rating may be exceeded by a large amount, potentially damaging or destroying the LED. The typical solution is therefore to use constant current power supplies, or driving the LED at a voltage much below the maximum rating. Since most household power sources (batteries, mains) are not constant current sources, most LED fixtures must include a power converter. However, the I/V curve of nitride-based LEDs is quite steep above the knee and gives an If of a few milliamperes at a Vf of 3 V, making it possible to power a nitride-based LED from a 3 V battery such as a coin cell without the need for a current limiting resistor.
As with all diodes, current flows easily from p-type to n-type material. However, no current flows and no light is produced if a small voltage is applied in the reverse direction. If the reverse voltage becomes large enough to exceed the breakdown voltage, a large current flows and the LED may be damaged. If the reverse current is sufficiently limited to avoid damage, the reverse-conducting LED is a useful noise diode.
The vast majority of devices containing LEDs are "safe under all conditions of normal use", and so are classified as "Class 1 LED product"/"LED Klasse 1". At present, only a few LEDs -- extremely bright LEDs that also have a tightly focused viewing angle of 8° or less -- could, in theory, cause temporary blindness, and so are classified as "Class 2". In general, laser safety regulations -- and the "Class 1", "Class 2", etc. system -- also apply to LEDs.
- Efficiency: LEDs produce more light per watt than incandescent bulbs.
- Color: LEDs can emit light of an intended color without the use of color filters that traditional lighting methods require. This is more efficient and can lower initial costs.
- Size: LEDs can be very small (smaller than 2 mm2) and are easily populated onto printed circuit boards.
- On/Off time: LEDs light up very quickly. A typical red indicator LED will achieve full brightness in microseconds. LEDs used in communications devices can have even faster response times.
- Cycling: LEDs are ideal for use in applications that are subject to frequent on-off cycling, unlike fluorescent lamps that burn out more quickly when cycled frequently, or HID lamps that require a long time before restarting.
- Dimming: LEDs can very easily be dimmed either by pulse-width modulation or lowering the forward current.
- Cool light: In contrast to most light sources, LEDs radiate very little heat in the form of IR that can cause damage to sensitive objects or fabrics. Wasted energy is dispersed as heat through the base of the LED.
- Slow failure: LEDs mostly fail by dimming over time, rather than the abrupt burn-out of incandescent bulbs.
- Lifetime: LEDs can have a relatively long useful life. One report estimates 35,000 to 50,000 hours of useful life, though time to complete failure may be longer. Fluorescent tubes typically are rated at about 10,000 to 15,000 hours, depending partly on the conditions of use, and incandescent light bulbs at 1,000–2,000 hours.
- Shock resistance: LEDs, being solid state components, are difficult to damage with external shock, unlike fluorescent and incandescent bulbs which are fragile.
- Focus: The solid package of the LED can be designed to focus its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a usable manner.
- Toxicity: LEDs do not contain mercury, unlike fluorescent lamps.
- High initial price: LEDs are currently more expensive, price per lumen, on an initial capital cost basis, than most conventional lighting technologies. The additional expense partially stems from the relatively low lumen output and the drive circuitry and power supplies needed.
- Temperature dependence: LED performance largely depends on the ambient temperature of the operating environment. Over-driving the LED in high ambient temperatures may result in overheating of the LED package, eventually leading to device failure. Adequate heat-sinking is required to maintain long life. This is especially important when considering automotive, medical, and military applications where the device must operate over a large range of temperatures, and is required to have a low failure rate.
- Voltage sensitivity: LEDs must be supplied with the voltage above the threshold and a current below the rating. This can involve series resistors or current-regulated power supplies.
- Light quality: Most cool- white LEDs have spectra that differ significantly from a black body radiator like the sun or an incandescent light. The spike at 460 nm and dip at 500 nm can cause the color of objects to be perceived differently under cool-white LED illumination than sunlight or incandescent sources, due to metamerism, red surfaces being rendered particularly badly by typical phosphor based cool-white LEDs. However, the color rendering properties of common fluorescent lamps are often inferior to what is now available in state-of-art white LEDs.
- Area light source: LEDs do not approximate a “point source” of light, but rather a lambertian distribution. So LEDs are difficult to use in applications requiring a spherical light field. LEDs are not capable of providing divergence below a few degrees. This is contrasted with lasers, which can produce beams with divergences of 0.2 degrees or less.
- Blue hazard: There is a concern that blue LEDs and cool-White LEDs are now capable of exceeding safe limits of the so-called blue-light hazard as defined in eye safety specifications such as ANSI/IESNA RP-27.1-05: Recommended Practice for Photobiological Safety for Lamp and Lamp Systems.
- Blue pollution: Because cool-white LEDs (i.e., LEDs with high color temperature) emit proportionally more blue light than conventional outdoor light sources such as high-pressure sodium lamps, the strong wavelength dependence of Rayleigh scattering means that cool-white LEDs can cause more light pollution than other light sources. The International Dark-Sky Association discourages the use of white light sources with correlated color temperature above 3,000 K.
Application of LEDs fall into four major categories:
- Visual signal application where the light goes more or less directly from the LED to the human eye, to convey a message or meaning.
- Illumination where LED light is reflected from object to give visual response of these objects.
- Generate light for measuring and interacting with processes that do not involve the human visual system.
- Narrow band light sensors where the LED is operated in a reverse-bias mode and is responsive to incident light instead of emiting light.
Indicators and signs
The low energy consumption, low maintenance and small size of modern LEDs has led to applications as status indicators and displays on a variety of equipment and installations. Large area LED displays are used as stadium displays and as dynamic decorative displays. Thin, lightweight message displays are used at airports and railway stations, and as destination displays for trains, buses, trams, and ferries.
The single color light is well suited for traffic lights and signals, exit signs, emergency vehicle lighting, ships' lanterns and LED-based Christmas lights. In cold climates, LED traffic lights may remain snow covered. Red or yellow LEDs are used in indicator and alphanumeric displays in environments where night vision must be retained: aircraft cockpits, submarine and ship bridges, astronomy observatories, and in the field, e.g. night time animal watching and military field use.
Because of their long life and fast switching times, LEDs have been used for automotive high-mounted brake lights and truck and bus brake lights and turn signals for some time, but many vehicles now use LEDs for their rear light clusters. The use of LEDs also has styling advantages because LEDs are capable of forming much thinner lights than incandescent lamps with parabolic reflectors. The significant improvement in the time taken to light up (perhaps 0.5 s faster than an incandescent bulb) improves safety by giving drivers more time to react. It has been reported that at normal highway speeds this equals one car length increased reaction time for the car behind. White LED headlamps are beginning to make an appearance. In an dual intensity circuit(ie. rear markers and brakes) if the LED's are not pulsed at a fast enough frequency, they can create a phantom array, where ghost images of the LED will appear if the eyes quickly scan across the array.
Due to the relative cheapness of low output LEDs, they are also used in many temporary applications such as glowsticks, throwies, and the photonic textile Lumalive. Artists have also used LEDs for LED art.
Weather/all-hazards radio receivers with Specific Area Message Encoding (SAME) have three LEDs: red for warnings, orange for watches, and yellow for advisories & statements whenever issued.
With the development of high efficiency and high power LEDs it has become possible to incorporate LEDs in lighting and illumination. Replacement light bulbs have been made as well as dedicated fixtures and LED lamps. LEDs are used as street lights and in other architectural lighting where color changing is used. The mechanical robustness and long lifetime is used in automotive lighting on cars, motorcycles and on bicycle lights.
LEDs have been used for lighting of streets and of parking garages. In 2007, the Italian village Torraca was the first place to convert its entire illumination system to LEDs.
LEDs are being used increasingly commonly for aquarium lighting. Particular for reef aquariums, LED lights provide an efficient light source with less heat output to help maintain optimal aquarium temperatures. LED-based aquarium fixtures also have the advantage of being manually adjustable to produce a specific color-spectrum for ideal coloration of corals, fish, and invertebrates while optimizing photosynethically active radiation (PAR) which increases growth and sustainability of photosynthetic life such as corals, anemones, clams, and macroalgae. These fixtures can be electronically programmed in order to simulate various lighting conditions throughout the day, reflecting phases of the sun and moon for a dynamic reef experience. LED fixtures typically cost up to five times as much as similarly rated fluorescent or high-intensity discharge lighting designed for reef aquariums and are not as high output to date.
LEDs are also being used now in airport and heliport lighting. LED airport fixtures currently include medium intensity runway lights, runway centerline lights and obstruction lighting.
LEDs are also suitable for backlighting for LCD televisions and lightweight laptop displays and light source for DLP projectors. RGB LEDs increase the color gamut by as much as 45%. Screens for TV and computer displays can be made increasingly thin using LEDs for backlighting.
The lack of IR/heat radiation makes LEDs ideal for stage lights using banks of RGB LEDs that can easily change color and decrease heating from traditional stage lighting, as well as medical lighting where IR-radiation can be harmful.
Since LEDs are small, durable and require little power they are used in hand held devices such as flashlights. LED strobe lights or camera flashes operate at a safe, low voltage, as opposed to the 250+ volts commonly found in xenon flashlamp-based lighting. This is particularly applicable to cameras on mobile phones, where space is at a premium and bulky voltage-increasing circuitry is undesirable. LEDs are used for infrared illumination in night vision applications including security cameras. A ring of LEDs around a video camera, aimed forward into a retroreflective background, allows chroma keying in video productions.
LEDs are used for decorative lighting as well. Uses include but are not limited to indoor/outdoor decor, limousines, cargo trailers, conversion vans, cruise ships, RVs, boats, automobiles, and utility trucks. Decorative LED lighting can also come in the form of lighted company signage and step and aisle lighting in theaters and auditoriums.
Light can be used to transmit broadband data, which is already implemented in IrDA standards using infrared LEDs. Because LEDs can cycle on and off millions of times per second, they can, in effect, become wireless routers for data transport. Lasers can also be modulated in this manner.
Efficient lighting is needed for sustainable architecture. A 13 watt LED lamp produces 450 to 650 lumens . which is equivalent to a standard 40 watt incandescent bulb . A standard 40 W incandescent bulb has an expected lifespan of 1,000 hours while an LED can continue to operate with reduced efficiency for more than 50,000 hours, 50 times longer than the incandescent bulb.
Environmentally friendly options
A single kilowatt-hour of electricity will generate 1.34 pounds (610 g) of CO2 emissions. Assuming the average light bulb is on for 10 hours a day, a single 40-watt incandescent bulb will generate 196 pounds (89 kg) of CO2 every year. The 13-watt LED equivalent will only be responsible for 63 pounds (29 kg) of CO2 over the same time span. A building’s carbon footprint from lighting can be reduced by 68% by exchanging all incandescent bulbs for new LEDs in warm climates. In cold climates, the energy saving may be lower, since more heating would be needed to compensate for the lower temperature.
LEDs are also non-toxic unlike the more popular energy efficient bulb option: the compact fluorescent a.k.a. CFL which contains traces of harmful mercury. While the amount of mercury in a CFL is small, introducing less into the environment is preferable.
LED light bulbs could be a cost-effective option for lighting a home or office space because of their very long lifetimes. Consumer use of LEDs as a replacement for conventional lighting system is currently hampered by the high cost and low efficiency of available products. 2009 DOE testing results showed an average efficacy of 35 lm/W, below that of typical CFLs, and as low as 9 lm/W, worse than standard incandescents. The high initial cost of the commercial LED bulb is due to the expensive sapphire substrate which is key to the production process. The sapphire apparatus must be coupled with a mirror-like collector to reflect light that would otherwise be wasted.
In 2008, a materials science research team at Purdue University succeeded in producing LED bulbs with a substitute for the sapphire components.. The team used metal-coated silicon wafers with a built-in reflective layer of zirconium nitride to lessen the overall production cost of the LED. They predict that within a few years, LEDs produced with their revolutionary, new technique will be competitively priced with CFLs. The less expensive LED would not only be the best energy saver, but also a very economical bulb.
Light has many other uses besides for seeing. LEDs are used for some of these applications. The uses fall in three groups: Communication, sensors and light matter interaction.
The light from LEDs can be modulated very quickly so they are used extensively in optical fiber and Free Space Optics communications. This include remote controls, such as for TVs and VCRs, where infrared LEDs are often used. Opto-isolators use an LED combined with a photodiode or phototransistor to provide a signal path with electrical isolation between two circuits. This is especially useful in medical equipment where the signals from a low voltage sensor circuit (usually battery powered) in contact with a living organism must be electrically isolated from any possible electrical failure in a recording or monitoring device operating at potentially dangerous voltages. An optoisolator also allows information to be transferred between circuits not sharing a common ground potential.
Many sensor systems rely on light as the signal source. LEDs are often ideal as a light source due to the requirements of the sensors. LEDs are used as movement sensors, for example in optical computer mice. The Nintendo Wii's sensor bar uses infrared LEDs. In pulse oximeters for measuring oxygen saturation. Some flatbed scanners use arrays of RGB LEDs rather than the typical cold-cathode fluorescent lamp as the light source. Having independent control of three illuminated colors allows the scanner to calibrate itself for more accurate color balance, and there is no need for warm-up. Furthermore, its sensors only need be monochromatic, since at any one point in time the page being scanned is only lit by a single color of light. Touch sensing: Since LEDs can also be used as photodiodes, they can be used for both photo emission and detection. This could be used in for example a touch-sensing screen that register reflected light from a finger or stylus.
Many materials and biological systems are sensitive to, or dependent on light. Grow lights use LEDs to increase photosynthesis in plants and bacteria and viruses can be removed from water and other substances using UV LEDs for sterilization. Other uses are as UV curing devices for some ink and coating applications as well as LED printers.
The use of LEDs is particularly interesting to plant cultivators, mainly because it is more energy efficient, less heat is produced (can damage plants close to hot lamps) and can provide the optimum light frequency for plant growth and bloom periods compared to currently used grow lights: HPS (high pressure sodium), MH (metal halide) or CFL/low-energy. It has however not replaced these grow lights due to it having a higher retail price, as mass production and LED kits develop the product will become cheaper.
LEDs have also been used as a medium quality voltage reference in electronic circuits. The forward voltage drop (e.g., about 1.7 V for a normal red LED) can be used instead of a Zener diode in low-voltage regulators. Red LEDs have the flattest I/V curve above the knee; nitride-based LEDs have a fairly steep I/V curve and are not useful in this application. Although LED forward voltage is much more current-dependent than a good Zener, Zener diodes are not widely available below voltages of about 3 V.
Light sources for machine vision systems
Machine vision systems often require bright and homogeneous illumination, so features of interest are easier to process. LEDs are often used to this purpose, and this field of application is likely to remain one of the major application areas until price drops low enough to make signaling and illumination applications more widespread. Barcode scanners are the most common example of machine vision, and many inexpensive ones used red LEDs instead of lasers. LEDs constitute a nearly ideal light source for machine vision systems for several reasons:
The size of the illuminated field is usually comparatively small and machine vision systems are often quite expensive, so the cost of the light source is usually a minor concern. However, it might not be easy to replace a broken light source placed within complex machinery, and here the long service life of LEDs is a benefit.
LED elements tend to be small and can be placed with high density over flat or even shaped substrates (PCBs etc) so that bright and homogeneous sources can be designed which direct light from tightly controlled directions on inspected parts. This can often be obtained with small, inexpensive lenses and diffusers, helping to achieve high light densities with control over lighting levels and homogeneity. LED sources can be shaped in several configurations (spot lights for reflective illumination; ring lights for coaxial illumination; back lights for contour illumination; linear assemblies; flat, large format panels; dome sources for diffused, omnidirectional illumination).
LEDs can be easily strobed (in the microsecond range and below) and synchronized with imaging. High power LEDs are available allowing well lit images even with very short light pulses. This is often used in order to obtain crisp and sharp “still” images of quickly-moving parts.
LEDs come in several different colors and wavelengths, easily allowing to use the best color for each application, where different color may provide better visibility of features of interest. Having a precisely known spectrum allows tightly matched filters to be used to separate informative bandwidth or to reduce disturbing effect of ambient light. LEDs usually operate at comparatively low working temperatures, simplifying heat management and dissipation, therefore allowing plastic lenses, filters and diffusers to be used. Waterproof units can also easily be designed, allowing for use in harsh or wet environments (food, beverage, oil industries).
Narrow band light sensors
The discovery and use of utilizing LED's as narrow band light sensors was pioneered by Forrest Mims. Mims was the first person to realize that LED's not only had the ability to emit light, but also to sense light. This dual-action (emission/detection) of LEDs or “Mims Effect” was unknown before his discovery.
Mims interest in LEDs began when he was experimenting with photosensitive devices back in 1962. In the "Backscatter" section in an online issue of The Citizen Scientist, Forrest Mims describes this himself:
While a high school senior in 1962, I first got the idea that light sensors should be able to double as light detectors. So I connected an automobile ignition coil to a cadmium sulfide photoresistor, switched on the power, and observed bright flashes of green light emitted by the semiconductor. The green flashes were distinctively different from the yellow flashes of an electrical arc.
While studying government (my major) in college, I found that certain silicon photodiodes can emit near-infrared radiation that can be detected by similar photodiodes. I managed to send modulated tones between such photodiodes. In 1971 I demonstrated the ability of many LEDs to detect light while experimenting with an optical fiber communication system. By placing a single LED at each end of the fiber, it was possible to send signals both ways through the fiber with only a single, dual purpose semiconductor device at each end of the fiber.
Later experiments by Mims were done in 1971, when he utilized two LEDs to perform bi-directional communication. In 1980, Mims demonstrated bi-directional LED voice communication through the air using near-infrared (940 nm) LEDs and also through a 100-meter section of optical fiber (650 nm). This demonstration was done at 1325 L Street in Washington D.C. – the exact same site where Alexander Graham Bell invented lightwave communications exactly 100 years earlier! Present for the demonstration, which was sponsored by the National Geographic Society, were representatives from National Geographic, the Smithsonian Institution and Bell Labs. Bell first demonstrated his Photophone on 3 June 1880.
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)


It is generally recommended to rinse your mouth with water after brushing to remove any food particles or toothpaste that may be left in your mouth. Rinsing your mouth can also help to freshen your breath.
However, it is important to note that you should not rinse your mouth with mouthwash immediately after brushing. This is because mouthwash can contain alcohol, which can cause the fluoride in toothpaste to be less effective. Fluoride is a mineral that helps to strengthen tooth enamel and prevent tooth decay.
To get the most benefit from your toothpaste and mouthwash, it is recommended to brush your teeth first, rinse your mouth with water, and then use mouthwash as directed. This allows the fluoride in the toothpaste to be absorbed by your teeth before rinsing it away with mouthwash.
If you have any concerns about your oral hygiene routine, it is always a good idea to consult with your dentist. They can provide personalised recommendations based on your individual needs.


On this page, we discuss the following ways to save energy as you use your kitchen:
Click a link in the list above to jump to that topic on this page.
Thawing food – Thaw food in the fridge. Put that frozen turkey to work for you! Reuse the energy spent to freeze your food by using it to help keep your fridge cool as it thaws.
You will also save on the energy needed to defrost the food item in an oven or microwave. An added benefit: thawing food in the refrigerator minimizes the growth of harmful bacteria.
Cooling leftovers – Do not put warm leftovers in to the fridge or freezer. Your appliance will have to expend energy just to cool the food to room temperature. Let the heat from cooking dissipate first, then put them in to chill.
Separate appliances – Never place your fridge next to a “hot” appliance like a stove or dishwasher. Your fridge will have to consume more energy to keep cool with a heat source next to it.
Smaller appliances – Smaller appliances use less energy. Many meals can be easily and efficiently cooked in an electric frying pan or toaster oven. Electric kettles are the best choice for boiling water. Downsizing your appliance use will add up to big energy savings.
EnerGuide – Buying energy efficient appliances is easy with Energy Star and EnerGuide labels.
Major electrical household appliances sold in Canada must meet minimum energy efficiency standards and are required to display an EnerGuide label. The labels show you how much electricity the appliance consumes in one year, and how the appliance compares to similar models in terms of energy consumption.
Fridge & freezer
Shut the door – We’re all guilty of “window shopping” for snacks. Leaving your fridge door open as you browse lets the cold air out and the warm air in. Once again, more energy must be spent to re-cool your fridge. Decide — then open the door.
Door seal – Test the door seal by putting a piece of paper between the door and the seal. If the bill falls down when the door is closed, your door needs to be corrected.
Stove & oven
Use lids – Unless the recipe calls for an uncovered pot or pan, always use lids to trap heat, speed cooking time, and save energy.
Size your pan – Your range has different-sized elements for a reason! Match the size of your pot or pan to the element for greater efficiency and more even cooking heat.
Turn off – Once the food is cooked, the oven will stay warm enough to keep your food piping hot with the oven off.
The same goes for food prepared on the stovetop. Cooked through? Keep it covered and shut the heat off.
Settings – Use the “energy saver” setting on your dishwasher. Always choose to save energy, water and money!
Air dry dishes – Prop open the door and dry your dishes — without spending a cent! The warm, moist air will be welcome during dry winter conditions. During the summer, minimize the heat added to your home by running the washer during the evening and skipping the heat-generating dry cycle.
Fill er’ up – Load your dishwasher full before running it. Remember, the machine uses the same amount of water and energy to wash a few dishes as it does for a full load. The same goes for laundry!


Adrien de Montmorency-Laval was a French army officer, before serving as French foreign minister and as an ambassador during the Bourbon Restoration.
His father was Lieutenant-General Anne-Alexandre de Montmorency, 2nd Duc de Laval, and his mother was Marie-Louise de Montmorency-Luxembourg (1750–1829).
Born in 1768 while his formidable great-grandfather, Marshal Guy-André-Pierre de Montmorency, the 1st duke was alive, Adrien was sent to be raised under the tuition of his uncle Cardinal Louis-Joseph de Montmorency-Laval, Prince-Bishop of Metz and Grand Almoner of France in preparation for taking holy orders.
Shortly after starting at the seminary of the Saint-Sulpice in Paris, his elder brother Guy de Montmorency, marquis de Laval, died unexpectedly in 1786; he had married Pauline-Renée-Sophie de Voyer de Paulmy d'Argenson in 1784. His brother's death, prompted him to leave church training and participate in court life at Versailles.
Montmorency-Laval joined the French army, being commissioned in the Alsace Cavalry Regiment, commanded by Charles, vicomte de Noailles (later duc de Mouchy) where he served alongside Marc-René de Voyer de Paulmy, marquis d'Argenson (1771–1842), his brother-in-law and lifelong friend.
On 14 May 1788, he married his second cousin (their great-grandfather was Anne-Jacques de Bullion, marquis de Fervacques, Governor of Marne), Bonne-Charlotte-Renée-Adélaïde de Montmorency-Luxembourg (1773–1840), daughter of Anne-Charles-Sigismond, duc de Piney-Luxembourg (1737–1803) and head of the senior branch of the Montmorencys, by his wife Madeleine-Suzanne-Adélaïde de Voyer de Paulmy d'Argenson.
The Duke and his wife had three children:Guy-Anne-Marie-Louis-Henri-Adalric, prince de Laval (1796–1819), Huntmaster of Morbihan;
Charlotte-Adélaïde (1798–1872), duquesa de San Fernando Luis, who married in 1817, Gustave de Lévis, marquis de Mirepoix: descendants include the historian, Antoine de Lévis-Mirepoix;
Marguerite-Emmanuelle-Pauline (1811–1861) married Aimé, marquis de Couronnel: ancestors of the Rarécourt family.
Through his wife's family (the Colignys) their descendants inherited great wealth, as both her elder brothers died childless and in 1791 her younger sister Marie-Madeleine married Miguel Caetano Álvares Pereira de Melo, 5th Duque de Cadaval, emigrating to Portugal.
Upon the outbreak of the French Revolution, after locating remaining family members in Paris, Adrien de Laval fled to England. As a French émigré in London, the marquis became friendly with the Prince of Wales and his circle.
During the revolutionary wars his father appointed him as aide-de-camp and despatched him to Italy as a captain in the Montmorency Regiment being stationed at Rome. After the ban on émigrés was lifted in 1800 he returned to France. Adrien de Laval was one of the first to congratulate Louis XVIII at Calais in 1814, and the king promoted him maréchal de camp (major-general) and bestowed on him the style of Prince de Montmorency-Laval; he succeeded to his father's dukedom in 1817.
On August 15, 1814, he was appointed French ambassador to Spain. There he came into conflict with Ceballos. But on receiving news of the return of Napoleon from Elba, a reconciliation was effected and Montmorency-Laval agreed to stay in Madrid, contrary to instructions from the French government. He successfully managed the somewhat tense relations between the Spanish Borbóns and the newly restored French Bourbons, being honoured in 1815 as a knight of the Golden Fleece and made duque de San Fernando Luis with the rank of grandee. His next ambassadorial posting was to Rome, where he arrived just before the end of Pius VII's reign and was present during the conclave for the election of his successor as pope; he supported the efforts of Austria in favour of Cardinal Castiglioni's candidacy. However, Cardinal Annibale della Genga was elected as Leo XII.
On 20 March 1828, the Duc de Laval was appointed French ambassador to Austria. His name was also mooted as a candidate to be king of Greece, but he twice refused King Charles X's proposals.
He was then posted as Ambassador to the Court of St James's, returning to Paris just before Charles X's exile. At Talleyrand's request, he dealt with unpleasant issues in London caused by his relatives, Louis, duc de Valençay and his father Edmond, duca di Dino, who had become addicted to gambling.
Declining to swear allegiance to King Louis-Philippe, the Duke and Duchess retired to the chateau de Montigny, where they received visitors, including Talleyrand. The Duke died on 16 June 1837 and, having been predeceased by his son at Naples in 1819, his youngest brother Eugène succeeded to his French titles before they became extinct, whereas his Spanish ducado and grandeza devolved upon his elder daughter and her descendants. Duke of France
Grandee of Spain
Count of the Holy Roman Empire
Grand Cross, Legion of Honour
Knight, Order of the Holy Spirit
Grand Cross, Order of Saint Louis
Knight, Order of Malta
Knight, Order of the Golden Fleece


In today’s globally connected world, language may still be a barrier to science.
Today, almost every major scientific journal prints in English – even while featuring research from all over the world. Meanwhile, new research suggests, tens of thousands of reports are being published without English translations. In a study published last week in the journal PLOS Biology, researchers argue that the permeation of English-language science has caused non-English studies to be overlooked.
“Language barriers continue to impede the global compilation and application of scientific knowledge,” lead author Tatsuya Amano, a professor of zoology at the University of Cambridge, said in a statement.
As part of their study, Dr. Amano and colleagues surveyed Google Scholar, a platform that by some estimates includes more than 100 million academic papers. They found that more than 75,000 studies on biodiversity conservation were published across 16 languages in 2014. About one third were published in non-English languages.
Of those, about 12.6 percent were published in Spanish. Another 10.3 percent were written in Portuguese, researchers found; Chinese and French accounted for 6 and 3 percent respectively. Researchers also found recent publications in Japanese, Korean, Italian, German, and Swedish – but only a few hundred per language.
“Scientific knowledge generated in the field by non-native English speakers is inevitably under-represented, particularly in the dominant English-language academic journals,” Amano said. “This potentially renders local and indigenous knowledge unavailable in English.”
In random sampling trials, researchers found that about half of non-English papers included titles or abstracts in English. The rest – about 13,000 documents – are completely unsearchable by English keywords.
“The real problem of language barriers in science is that few people have tried to solve it,” Amano said. “Native English speakers tend to assume that all the important information is available in English. But this is not true, as we show in our study.”
“On the other hand, non-native English speakers, like myself, tend to think carrying out research in English is the first priority, often ending up ignoring non-English science and its communication.”
English wasn’t always the lingua franca, or common language, of science. During the Renaissance, Latin was understood most universally by academics. Galileo, for example, translated his studies to Latin so that non-Italian scientists could follow his work.
By the early 1900s, most scientific studies were published in German. But in the post-war years, as Germany’s global influence waned, English took the lead.
Today, this linguistic dominance is widely acknowledged. In 2013, the French Parliament considered a bill that would allow public university science classes to be taught in English. Bastien Inzaurralde reported for The Christian Science Monitor:
Supporters – including two Nobel Prize winners – of the measure say it would not only make France more attractive for talented students and scholars who don’t speak French, but also help French students prepare to work in an English-speaking environment.
But doubling down on English may not be the best way to overcome the language barrier, researchers say. Instead, they argue, journals should supply translations of current scientific publications. To emphasize that point, authors included summaries of their new study in Spanish, Portuguese, Chinese, Japanese, and French.
“While we recognise the importance of a lingua franca, and the contribution of English to science, the scientific community should not assume that all important information is published in English,” Amano said.
Researchers say universities and funding institutions should encourage translations as part of “public outreach,” particularly when it comes to global trends and non-English regions.
“We should see this as an opportunity as well as a challenge,” Amano said. “Overcoming language barriers can help us achieve less biased knowledge and enhance the application of science globally.”


of the Marian generals gave him the wished-for opportunity ; he was surrounded by three armies, commanded respectively by M. Brutus, C. Caelius Caldus, and C. Carrinas, whose great object seems to have been to prevent his escape to Sulla. Pompey now displayed for the first time the great military abilities for which he became afterwards so conspicuous ; he concentrated all his forces in one spot, and then fell upon M. Brutus at a time when he could receive no assistance from the other generals, and completely defeated him. Pompey also distinguished himself by his personal bravery in this engagement, charging at the head of his cavalry, and striking down a Celtic horseman with his own hand. The Marian generals, after the loss of this battle, quarrelled among themselves, and withdrew from the country. Pompey, who had no longer an enemy to oppose him, set out to join Sulla, and was hailed as a deliverer by the towns of Picenum, who had now no other alternative but submission. He was proscribed by the senate, but his troops proved faithful to him, and he joined Sulla in safety, having already gained for himself a brilliant reputation. He was received by Sulla with still greater distinction than he had anticipated ; for when he leapt down from his horse, and saluted Sulla by the title of Imperator, the latter returned the compliment by addressing him by the same title. Pompey was only twenty-three, and had not held any public office when he received this unprecedented mark of honour.
Next year, b. c. 82, the war was prosecuted with vigour against the Marian party. Pompey took a prominent part in it as one of Sulla's legates, and by his success gained still further distinction. The younger Marius, who was now consul, was blockaded in Praeneste, and his colleague, Carbo, was making every effort to relieve him. Sulla himself fought an indecisive battle against Carbo; but his legates, Marcius and Carrinas, were defeated by Pompey. Carbo then retreated to Ariminum, and sent Marcius to the relief of Praeneste; but Ponmpey defeated the latter again in the Apennines, and compelled him to retire. Despairing of success, Carbo then abandoned Marius to his fate, and set sail for Africa. Praeneste shortly afterwards surrendered. Sulla thus became the master of Italy, and was proclaimed dictator. He then proceeded to reward his partizans, and to take vengeance on his enemies; and in order to connect Pompey more closely with himself, he compelled him to marry his step-daughter Aemilia, the daughter of his wife Caecilia Metella, by her former husband Aemilius Scaurus. To effect this marriage two divorces had to take place: Pompey was obliged to put away his wife Antistia, though her father had been murdered by Marius as a partizan of Sulla, simply on account of his connection with Pompey; and Aemilia was obliged to leave her husband M'. Glabrio, although she was pregnant at the time. Aemilia died shortly afterwards in child-birth.
But although the war in Italy was brought to a close, the Marian party still held out in other parts of Europe; and Pompey, who was now regarded as one of the principal leaders of the aristocracy, was sent against them by Sulla. He first proceeded to Sicily, to which island Carbo had crossed over from Africa, but here met with no opposition; as soon as he landed, Carbo fled from the island, intending to take refuge in Egypt, but he was seized and brought in chains to Pompey, at Lilybaeum, who put him to death, and sent his head to Sulla. He likewise executed several others of the Marian party; but he can scarcely be reproached with cruelty for so doing, as he had no other alternative, even if he had wished to save them; and he treated the cities which had espoused the popular side with greater leniency than might have been expected. Next year, b. c. 81, Pompey left Sicily, and passed over to Africa, in order to oppose Cn. Domitius Ahenobarus the son-in-law of Cinna, who, with the assistance of Hiarbas, had collected a formidable army. But his troops, chiefly consisting of Numidians, were no match for the veterans who had conquered the well-disciplined Italian allies. Still they fought with great bravery, and out of 20,000 only 3000 are said to have survived the decisive battle. Their camp was taken, and Domitius fell. In a few months Pompey reduced the whole of Numidia ; Hiarbas was taken prisoner and put to death, and his throne was given to Hiempsal. But it was not only his military achievements that gained him great renown at Rome; unlike other Roman governors, he abstained from plundering the province, which seemed the more extraordinary, since the disturbed state of the country afforded him particular facilities for doing so. Intent upon triumphing, he collected a great number of elephants and lions in Numidia, and returned to Rome, in the same year, covered with glory. As he approached Rome, numbers flocked out of the city to meet him; and the dictator himself, who formed one of the crowd, greeted him with the surname of Magnus, which he bore ever afterwards, and handed down to his children. But Pompey did not find it easy to obtain his wished-for triumph. Hitherto no one but a dictator, consul, or praetor, had enjoyed this distinction, and it seemed a monstrous thing for a simple eques, who had not yet obtained a place in the senate, to covet this honour. Sulla at first tried to dissuade Pompey from pressing his request; and as he would not relinquish his design, the matter was referred to the senate, and there Sulla positively opposed it. Pompey was not, however, to be cowed, and uttered a threat about the rising and the setting sun; whereupon Sulla, indignant at his impudence. shouted out contemptuously, "Let him triumph then !" It is true that Sulla's dominion was too firmly established to be overthrown by Pompey ; but he probably could not have put him down without a struggle, and therefore thought it better to let him have his own way. Pompey therefore entered Rome in triumph as a simple eques in the month of September b. c. 81, and before he had completed his twenty-fifth year. Pompey's conduct in insisting upon a triumph on this occasion has been represented by many modern writers as vain and childish but it should be recollected that it was a vanity which all distinguished Romans shared, and that to enter Rome drawn in
- There can be little doubt that this surname was given to Pompey on this occasion, though many writers assign it to a different time. The question is discussed at length by Drumann, vol. iv. p. 335. Pompey did not use it himself till he was appointed to the command of the war against Sertorius (Plut. Pomp. 13).


The reminiscence bump is the tendency for older adults to have increased recollection for events that occurred during their adolescence and early adulthood. It was identified through the study of autobiographical memory and the subsequent plotting of the age of encoding of memories to form the lifespan retrieval curve.The Life Span Retrieval Curve is a graph that represents the number of autobiographical memories encoded at various ages during the life span. The lifespan retrieval curve contains three different parts. From birth to five years old is a period of childhood amnesia, from 10 to 30 years old is the reminiscence bump and last is a period of forgetting from the end of the reminiscence bump to present time. The reminiscence bump has been observed on the life span retrieval curve in multiple studies.The reminiscence bump occurs because memory storage in autobiographical memory is not consistent through time. Rather, memory storage increases during times of changes in the self and in life goals, such as the changes in identity that occur during adolescence.Researchers have consistently observed the reminiscence bump, the period of increased memory accessibility in participants' lifespan retrieval curves, and the bump has been reproduced under a range of study conditions.


Circa 1820: Our records and logic argue that the “new” brick wing of the house was built in 1817-1820.
The symbolism of the house addition: the new half is taller than the old. Its roof looms over the other half. Inside, there is a dramatic three-step rise into what is now the living room or front parlor. The same step up exists upstairs, from one bedroom and hallway up into the new grander bedroom.
The new half is brick – no attempt made to match the fronts, instead relying on the new, sturdier, more impressive, more dramatic brick front.
A new grand front porch unites the two, presenting a look of a statelier, grander edifice than before.
The new wing seems to represent a bold swagger – gone is the utilitarian humble pile within which an erudite attorney like William Roane could read law while running several farms. Gone the single frame abode where the hardworking Spencer grew up, focusing on both schoolwork with his Scottish tutor and on cutting down the trees around the plantation.


notes on the Jack Russell terrier
Russell is a small, compact, athletic dog and looks like a less refined working
Fox Terrier. White (at least 51%) with reddish black, tan, or brown markings,
especially in the head and tail. The skull is flat between the ears, then
tapering. The stop is defined, but not abrupt. The nose is black and the almond-shaped
eyes are dark. The v-shaped ears fold forward. The Jack Russell has a flexible
body and fairly small chest (easily spanned by the average man's hands) to
enable him to go to ground after his prey. The docked tail is carried gaily
and set fairly high. Comes in smooth, broken, and wire-haired varieties. The
broken coat is a cross of rough and smooth coat - long body hair, a slightly
fuzzy face and a smooth head. An Irish-type called Jack Russell Shortys have
shorter legs than the English-type.
The Jack Russell Terrier is a perky, merry, devoted, and loving dog. Spirited and obedient, yet absolutely fearless. Careful and amusing, he enjoys games and playing with toys. Friendly and generally kind to children who have been taught not to tease or strike the dog. They are intelligent, yet willful and determined. They can be slightly difficult to train and need a firm, experienced trainer. The Jack Russel can be aggressive with other dogs if not well trained and socialized. Some have killed or been killed in dog fights. Early socialization can help substantially moderate this trait. They have strong hunting instincts (stronger than your average terrier) and should not be trusted with other small animals. They like to chase and explore. Be careful not to let them off the lead unless they are very well-trained. Jack Russells like to bark and dig. They tend to get restless and destructive if not kept fruitfully occupied and well exercised. Jack Russells climb, which means they can climb over a fence, they also jump. A Jack that stands 12 inches high can easily jump five feet. JRTs are not the breed for a inexperienced dog owner. This is a BIG dog in a little dogs body. The owner needs to be as strong-willed as they are, or this little guy will take over. With the right owner this little dog can really excel, but is not recommended for those who have not had prior experience with terriers.
The Jack Russel Terrier was developed in 19th century England by a clergyman named Jack Russell. This feisty little terrier was used to hunt small game, particularly fox, by digging the quarry out of its den. Breeders have emphasized its working ability, so the standard is very broad, encompassing a wide range of accepted body types. On English hunts, the Jack Russell Terriers were supposed to be long-legged enough to keep up with the hounds.ĘThe energetic and playful Jack Russell makes a good family companion. Some of the Jack Russell's talents include: hunting, tracking, agility, and performing tricks.
of two Jack Russell Terriers
Two beautiful litter mates.
more terrier portraits and other dog breeds -
visit the dog painting gallery
designed by paintmydog © justine osborne 2002 - 2013
all dog portraits, pictures, photos and text not to be reproduced without permission from the artist


Fluorescent markers, sometimes known as fluorophores, is any molecule with the ability to absorb light and emit it at some other well defined wavelength. Flurophores come in a variety of types ranging from simple organic compounds to large proteins like Green Fluorescent Protein. Fluorescent markers give the ability to investigate in their biological environment. When light of a certain wavelength is directed at the molecule's chromophore, a photon is absorbed and excites an electron to a higher energy state. The electron then relaxes back to its ground state. The energy that is released is determined by the formula E = hν, where h is Planck's constant and ν is the frequency of the photon. This energy can then be related back to the wavelength of the emitted photon, which corresponds to a specific color on the visible spectrum. The difference between the absorption and emission wavelength is called the Stokes shift. Large Stokes shifts are generally desirable because the emitted light from the fluorescent tag can be filtered out more easily from the excitation light. Fluorescence educing molecules such as FITC (fluorescein isothiocyanate) are used to stain cells which give the ability to examine these cells under a fluorescence microscope. Multiple fluorescent markers can be used to stain different parts of cell. Fluorescence microscopy can aid in determining the location of specific proteins within a cell. One can even track the movement of these proteins and derive possible functions for these proteins of interest.


The Workbook object lies at the top of the hierarchy of the Excel 2010 VBA objects. We will deal with properties and methods associated the Workbook object.
When we write Excel 2010 VBA code involving the Workbook object, we use Workbooks.
The reason is that we are dealing with a collection of workbooks most of the time, so using Workbooks enables us to manipulate multiple workbooks at the same time.When will deal with multiple workbooks, we can use indices to denote different workbooks that are open, using the syntax Workbooks (i), where i is an index. For example, Workbooks (1) denotes Workbook1, Workbooks (2) denotes Workbook2 and more.
Workbooks have a number of properties. Some of the common properties are Name, Path and FullName Let’s look at the following example:
Private Sub CommandButton1_Click() MsgBox Workbooks(1).Name End Sub
The program will cause a message dialog box to pop up and displays the first workbook name, i.e. Book1 as shown in Figure 20.1 below:
If we have only one open workbook, we can also use the syntax ThisWorkbook in place of Workbook (1), as follows:
Private Sub CommandButton1_Click () MsgBox ThisWorkbook.Name End Sub
Private Sub CommandButton1_Click () MsgBox ThisWorkbook.Path End Sub
Or you can use the following code:
Private Sub CommandButton1Click () MsgBox Workbooks (“Book1”).Path End Sub
This example will display the path and name of the opened workbook. The code is:
Private Sub CommandButton1_Click () MsgBox ThisWorkbook.FullName End Sub
Private Sub CommandButton1Click() MsgBox Workbooks(“Book1”).Fullname End Sub
There are severl methods associated with the workbook object. These methods are Save, SaveAs, Open, Close and more.
In this example, when the user clicks on the command button, it will open up a dialog box and ask the user to specify a path and type in the file name, and then click the save button, not unlike the standard windows SaveAs dialog, as shown in Figure 20.4.
Private Sub CommandButton1_Click() fName = Application.GetSaveAsFilename ThisWorkbook.SaveAs Filename:=fName End Sub
Another method associated with the workbook object is open. The syntax is
Workbooks.Open (“File Name”)
In this example, when the user click on the command button, it wil open the file book1.xls under the path C:\Users\Toshiba\Documents\Liew Folder\VBA\vba2010\
Private Sub CommandButton1_Click() Workbooks.Open ("C:\Users\Toshiba\Documents\Liew Folder\VBA\vba2010\book1.xlsx") End Sub
The close method is the command that closes a workbook. The syntax is
In this example, when the user clicks the command button, it will close Workbooks (1).
Private Sub CommandButton1_Click() Workbooks (1).Close End Sub


Almost everybody knows the value of c that is 300,000 Km/sec. Means just impossible to even imagine.
On earth, it is not possible for something to achieve the speed of light. But if let us suppose an object moving with c then what’s about the object?
So, the strange thing is this that the object will disappear, but why?
The answer for its invisibility is cleared by the concept of LENGTH CONTRACTION. It provides us a relation between the rest length, its velocity and between speed of light.
By this concept, we get the approximate lenght of an object moving with speed of light as ZERO.
Hence, light is the biggest mystery even now. As, we didn’t get any visible object till now moving with c.


The images below show the basic topography of the Cape Peninsula from Table Bay looking south over Cape Town and Table Mountain towards the Cape of Good Hope. The particular features are the Table Mountain massif and the chain of mountains that runs down the spine of the peninsula. Table Mountain rises 3,558 feet (1,085 m).
To the left of the mountains is the broad expanse of the Cape Flats that joins the peninsula at Muizenberg.
In the front of the image is Table Bay and Cape Town Harbour. To their right is Green Point and the polo-mint surrounded-by-green that is the spectacular Green Point Stadium built for the 2010 FIFA World Cup. Behind this is Signal Hill and Lion's Head and the west coast suburbs of Camps Bay and Bakoven.
The topography of the penisula is brought into sharper relief in the aerial view below that shows the tremendous bulk of Table Mountain and the right fork of the mountains running down to Hout Bay and the Chapman's Peak Drive (see Driving Chapman's Peak). To the left the mountains snake down through Constatia (see Wine and Land I) and the wine country on the eastern slopes before meeting False Bay at Muizenberg. Beyond is Simon's Town bay (see Birds I: African Penguins) and the steep eastward facing slopes, from where we saw the dolphin and gannet feeding frenzy (see Mammals VI: Dolphins), between Simon's Town and Smitswinkel Bay. Beyond are the lower hills that run out to the cliffs at Cape Point.
The image below gives a schematic representation of the geology of the peninsula. The oldest rocks are the late-Precambrian Malmesbury Group made up of alternating layers of dark grey fine-grained greywacke sandstone and slate. These underly most of the peninsula.
Next are Peninsula Granites which were intruded as a huge batholith into the Malmesbury Group about 630 million years ago as molten rock which then crystallized deep in the earth. It has since been exposed by prolonged erosion and can be seen at places such as Boulders Beach at Simon's Town (see Penguins). It was also quarried from the base of Table Mountain by a Cornish quarryman (see Gone Bulawayo on the Cornish in South Africa ) for the construction of the Rhodes Memorial (see Rhodes Memorial ) on the edge of Cape Town.
The Table Mountain Group sandstones - blue in the image) were deposited onto the eroded surface of the granite and Malmesbury basement.They are made up of two formations:
The yellow areas represent Extensive sands laid down during the Pliocene and subsequent Pleistocene ice-ages between 2 million and 15000 years ago when sea-levels fluctuated between -120 to +200 m from present mean sea level. At times the sea covered the Cape Flats the Cape Peninsula was then a group of islands.
Each of the rock and sand types listed above is associated with different fynbos types which have different characteristic plants. The sands give rise to a variety of sand and sandveld fynbos types. As do the granites, sandstones and Malmesbury slates and shales. Topography and orientation also play a part - for example there is a 3000+ ft elevation difference between the top of Table Mountain and Buffels Bay near Cape Point. Similarly there are great differences between east and west facing slopes - the west get the colder winter westerlies whereas the easterlies get the warmer south-easterly trade winds. Water avalability is also crucial - wetter ground will abound in restios while dry sands may only be able to support succulents and bulb-rooted plants.


A small river in eastern Massachusetts which empties into the Altantic at the northwestern end of Buzzards Bay; and a town in Hampden County, Mass. Agawam is an Indian word meaning lowland, marsh, or meadow.
The first Agawam, a double-ended, side-wheel, gunboat built at Portland, Maine, by George W. Lawrence, was laid down in October 1862; launched on 21 April 1863; and commissioned on 9 March 1864, Comdr. Alexander C. Rhind in command.
On 9 December 1863, some three months before Agawam was placed in full commission, Southern agents and sympathizers had boarded the steam packet Chesapeake at New York under the guise of being passengers bound for Portland, Maine. Shortly after midnight on the 7th, when the liner had reached a point some 20 miles north of the tip of Cape Cod, these men revealed their formerly concealed side arms and took over the ship, killing her second engineer. From there, they took the ship to Canadian waters in the hope that their daring act would provoke Union warships into violating British neutrality and thereby embroil the United States in a war with England.
When word of Chesapeake's capture reached Portland, the deputy collector of customs at that port wired Rear Admiral Francis Hoyt Gregory, the supervisor of construction of all Union warships then being built in private shipyards, informing him of the loss and requesting permission to arm, man, and send out in pursuit the unfinished but seaworthy Agawam. Temporary arms, officers, and men for the new warship would come from the revenue cutter James C. Dobbin which had arrived at Portland in July.
The Navy's extant records seem to contain no report of Agawam's chase of Chesapeake, if, indeed, she ever did join the hunt for the stolen ship. The flurry of Federal correspondence stirred up by the audacious Confederate coup contains both statements maintaining that she did at least get underway and evidence indicating that she did not. Thus, her role in the Chesapeake affair, if any, will remain a mystery unless now unknown documents come to light.
In any case, after being commissioned, Agawam remained in the Portsmouth Navy Yard fitting out until standing down Portsmouth harbor on 17 March. However, she returned to the yard two days later and entered drydock for repairs before heading back to Portland on 18 April.
Assigned to the North Atlantic Blockading Squadron, the steamer finally stood out to sea on 6 May, two days after the Army of the Potomac crossed the Rapidan River to begin General Grant's offensive against Richmond which kept unrelenting pressure on General Robert E. Lee's Army of Northern Virginia until it was bottled up in the siege of Petersburg and finally forced it to surrender at Appomattox. Agawam would perform most of her Civil War service in support of this drive.
When she was finally deemed ready for active service, the gunboat departed Portland on 6 May, only two days after Grant's troops crossed the Rapidan and the day after troops led by Major General Benjamin F. Butler landed on Bermuda Hundred, a large neck of land between the James and its tributary, the Appomattox River. This territory was strategically located some 15 miles south of Richmond and about seven miles north of Petersburg, probably the last important railroad center remaining in Southern hands. Butler's operation was designed to cut the railroads and to take or, at least, to threaten these vital Confederate cities. General Grant, then General-in-Chief of the United States Army, hoped that Butler's campaign would, as a bare minimum, interrupt the flow of food from the deep south and the west through Richmond to Lee's troops. According to this plan, if Butler did not take the Confederate capital, his operations would draw significant troops away from Lee's Army, starve it, and so weaken it that the Union force pushing down from the Rapidan would be able to overrun Richmond or link up with Butler and join in investing these key Southern cities. In any case, even moderate success on Butler's part should quickly end the war.
But moderate success for Butler was not forthcoming. By the time Agawam reached Hampton Roads on 9 May, the Union commander had squandered his initial advantage of surprise by his hesitation to launch vigorous attacks toward his initial objectives, the railroad and the turnpike connecting Petersburg and Richmond. This delay enabled the Confederacy to bring major reinforcement to their previously almost undefended works in the area. Then, the presence of Southern soldiers in the area prompted Butler to remain within strong defensive lines where he could do almost nothing to help the Army of the Potomac as it fought its way toward Richmond in a series of bloody engagements beginning with the Battle of the Wilderness.
Meanwhile, it was the task of the Union Navy to maintain control of the James lest Butler's 30,000 troops at Bermuda Hundred be cut off and annihilated. Agawam reached Hampton Roads on 9 May and two days later stood up the James to join other Union ships in protecting Butler's transports and supply ships which were threatened by torpedoes, shore batteries, and a possible attack by Confederate ironclads which were lying in the river above the Confederate batteries of Fort Darling at Drewry's Bluff. The danger lurking in the muddy waters of the James had recently been emphasized by the sinking of Commodore Jones on the 6th while that side-wheel ferryboat was dragging for Southern torpedoes, or, in 20th century parlance, mines.
On the 14th, Rear Admiral Samuel Phillips Lee, the commander of the North Atlantic Blockading Squadron, shifted his flag from Malvern to Agawam since the latter drew less water and thus would enable him to supervise minesweeping operations more closely, and he remained in the new side-wheeler while giving his primary attention to operations in the James during the ensuing month and one-half. Agaivam's first combat came at dawn on the 18th when she shelled Confederate forces ". . . intrenching the heights at Hewlett's house, commanding Trent's Reach," a straight stretch of the river flowing east along the northeastern section of Bermuda Hundred. During this time, besides serving as the squadron flagship, she helped to clear the river of mines, was a mobile platform for observation of Confederate activity along both banks of the river, acted as an intelli-gence and communication clearinghouse, and used her guns to suppress Southern batteries ashore.
From first planning to land a force at Bermuda Hundred, General Butler had been fearful that Confederate warships might descend from Richmond and sink his transports and supply ships. Once his troops were actually ashore on the south side of the river, the general's anxiety was intensified by daily rumors reporting that the South was ready to launch just such an offensive. For instance, late in May, a deserter from the Southern gunboat Hampton warned that". . . the enemy have now below Drewry's Bluff three ironclads, six smaller gunboats, plated with boiler iron ... all mounted with torpedoes, and nine fire ships ... to attack at as early a moment as practicable . . . ."
Confident in the ability of his warships, Admiral Lee was eager to meet the Southern squadron and was hopeful that his flotilla might ascend James past the batteries at Drewry's Bluff and capture Richmond himself the way Farragut had taken New Orleans. As a result, he constantly opposed obstructing the channel. However, early in June, Grant decided to shift the Army of the Potomac from its lines at Cold Harbor across the James to join Butler in operations against Richmond from the South. This plan made Union control of the River even more important and prompted Washington to insist upon blocking the channel. The first stone-laden schooner was sunk on 15 June and the operation continued until Army leaders felt safe from Southern ironclads.
This barrier increased the security of Union shipping on the James and reduced the burden on the Union warships on the river, freeing Admiral Lee to attend to squadron matters elsewhere. As a result, he shifted his flag back to Malvern on the last day of June and returned to Hampton Roads.
Agawam remained upriver where, despite the obstructions, she found ample opportunity to use her fighting skills. The presence of the tremendous concentration of Union troops south of Richmond had goaded defenders of the Confederate capital into desperate measures to interrupt Union shipping on the James. The day after Admiral Lee left her, Agawam and Mendota fired on a fortified position inside Four Mile Creek whence Southern five guns had recently fired upon Hunchback and, in the months that followed, frequently engaged batteries hiding along the banks of the strategic stream.
Early in July, Lt. George Dewey, the future hero of Manila Bay, relieved Rhind in temporary command of the ship, his first command, but Rhind was back when Agawam fought her most memorable battle. About two hours past noon on 13 August, three batteries opened fire on the double-ender almost simultaneously from different locations, beginning an engagement which lasted over four hours before dwindling ammunition forced her to withdraw. During the action, three of Agawam's men were killed and four wounded.
Late in November, boiler trouble forced Agawam downstream for extensive repairs. While the ship was being brought back to fighting trim in the Norfolk Navy Yard, Comdr. Rhind left her temporarily to take command of Louisiana, a steamer which had been selected to perform an unusual and seemingly important task. Rhind took with him a carefully selected group of volunteers from Agawam to man his new ship. They boarded Louisiana at Beaufort, N.C., and took her to waters of Wilmington, N.C., for use as a giant bomb to help reduce the defenses of Fort Fisher which guarded that city, the only major port still open to Confederate blockade runners. After several days of delay because of stormy weather, Rhind took the ship close aboard Fort Fisher on the night of 23 and 24 December 1864. Her crew then set her ablaze, left the ship, and managed to row to safety before Louisiana exploded.
The concussion failed to detonate the Fort Fisher magazine, and the ensuing amphibious attack proved to be abortive. The troops who went ashore on Christmas Eve to storm the Southern stronghold reembarked the next day and headed back toward Hampton Roads. Rhind and band of daring volunteers returned to Agawam which was still undergoing repairs.
The work continued through mid-February, and the gunboat finally put to sea on the 16th. She entered Pamlico Sound, N.C., two days later and operated in the island waters of that state through the end of the Civil War.
Following the collapse of the Confederacy, Agawam operated along the Atlantic coast between Florida and the Virginia capes for almost two years. She was decommissioned at Norfolk on 31 March 1867. The ship was sold at auction there on 10 October 1867 to Mr. James Power. No record of her subsequent career has been found.