A light-emitting diode LED is a semiconductor light source that emits light when current flows through it. Electrons in the semiconductor recombine with electron holesreleasing energy in the form of photons. The color of the light corresponding to the energy of the photons is determined by the energy required for electrons to cross the band gap of the semiconductor.
Appearing as practical electronic components inthe earliest LEDs emitted low-intensity infrared IR light. The first visible-light LEDs were of low intensity and limited to red.
Modern LEDs are available across the visibleultraviolet UVand infrared wavelengths, with high light output.LEDs - Light Emitting Diodes - Basic Introduction
Early LEDs were often used as indicator lamps, replacing small incandescent bulbs, and in seven-segment displays. Recent developments have produced high-output white light LEDs suitable for room and outdoor area lighting.
LEDs have led to new displays and sensors, while their high switching rates are useful in advanced communications technology. LEDs have many advantages over incandescent light sources, including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching.
LEDs are used in applications as diverse as aviation lightingautomotive headlampsadvertising, general lightingtraffic signalscamera flashes, lighted wallpaperhorticultural grow lightsand medical devices. Unlike a laserthe light emitted from an LED is neither spectrally coherent nor even highly monochromatic.
However, its spectrum is sufficiently narrow that it appears to the human eye as a pure saturated color. Electroluminescence as a phenomenon was discovered in by the British experimenter H. Round of Marconi Labsusing a crystal of silicon carbide and a cat's-whisker detector. InGeorges Destriau observed that electroluminescence could be produced when zinc sulphide ZnS powder is suspended in an insulator and an alternating electrical field is applied to it.
In his publications, Destriau often referred to luminescence as Losev-Light. Destriau worked in the laboratories of Madame Marie Curiealso an early pioneer in the field of luminescence with research on radium.
Kurt LehovecCarl Accardo, and Edward Jamgochian explained these first LEDs in using an apparatus employing SiC crystals with a current source of a battery or a pulse generator and with a comparison to a variant, pure, crystal in Rubin Braunstein  of the Radio Corporation of America reported on infrared emission from gallium arsenide GaAs and other semiconductor alloys in InBraunstein further demonstrated that the rudimentary devices could be used for non-radio communication across a short distance.
As noted by Kroemer  Braunstein "…had set up a simple optical communications link: Music emerging from a record player was used via suitable electronics to modulate the forward current of a GaAs diode. The emitted light was detected by a PbS diode some distance away. This signal was fed into an audio amplifier and played back by a loudspeaker. Intercepting the beam stopped the music. We had a great deal of fun playing with this setup.
After establishing the priority of their work based on engineering notebooks predating submissions from G. 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 Pearsall designed the first high-brightness, high-efficiency LEDs for optical fiber telecommunications by inventing new semiconductor materials specifically adapted to optical fiber transmission wavelengths.
The first commercial visible-wavelength LEDs were commonly used as replacements for incandescent and neon indicator lampsand in seven-segment displays first in expensive equipment such as laboratory and electronics test equipment, then later in such appliances as calculators, TVs, radios, telephones, as well as watches see list of signal uses. Borden, Gerald P. Pighini and Mohamed M. Atalla left HP and joined Fairchild Semiconductor in These devices employed compound semiconductor chips fabricated with the planar process developed by Jean Hoerni  based on Atalla's surface passivation method  .
The combination of planar processing for chip fabrication and innovative packaging methods enabled the team at Fairchild led by optoelectronics pioneer Thomas Brandt to achieve the needed cost reductions. The early red LEDs were bright enough only for use as indicators, as the light output was not enough to illuminate an area.
Readouts in calculators were so small that plastic lenses were built over each digit to make them legible. Later, other colors became widely available and appeared in appliances and equipment. Early LEDs were packaged in metal cases similar to those of transistors, with a glass window or lens to let the light out. Modern indicator LEDs are packed in transparent molded plastic cases, tubular or rectangular in shape, and often tinted to match the device color.In: Science.
Led marketing directorIntroduction p. Mission and objectives p. Capabilities of our company p. Current Marketing Situation p. Positioning p. Marketing Strategy p. Product Strategy 2. Pricing strategy 3. Promotion strategy 4. Distribution strategy VII. Budgets p. Controls p. Executive Summary p. References p.
Light Emitting Diode Basics
Introduction What is LED light? With a view to creating a better quality of light and saving energy LED light has entered the light industry. Full form of LED is light emitting diode. The concept of LED is pretty simple.
As electricity flows from the p part to the n part, holes from the p part meet the electrons from the n part. When the holes and electrons meet, they radiate energy. In LED, this energy is used as light. But untilLEDs were very costly and inefficient for commercial and personal use. After that, there had been quite some developments in LED technology resulting in the efficiency to rise exponentially with a doubling Capabilities of our company p The use of national standards and test methods improves consistency of performance and facilitates product comparisons, thereby increasing consumer confidence and satisfaction.
As the technology matures, standards and guidelines are created or revised as needed. The documents listed here are those applicable in North America and completed as of October ANSLG was initially created through the ANSI organization to support development of appropriate and needed lighting standards through its own working group s or other organizations.
Fiber optic light sources must be able to turn on and off millions to billions of times per second while projecting a nearly microscopic beam of light into an optical fiber. Both Light Emitting Diodes and Laser transmitters are considered to be semiconductor light sources. However, they differ greatly in output patterns. The photons that are emitted are out of phase and not launched in the same direction. This is called incoherent light. Only a small percentage of this light is actually coupled into the optical fiber since incoherent light is difficult to focus.
There are two types of LEDs, surface emitting and edge emitting. Because of this, incoherent photons radiate from all points of the junction. Edge emitting LEDs are formed from similar materials with different refractive indexes. These indexes are used to guide the light and create a directional output.
Light is emitted though an etched opening in the diode.These metrics are regularly updated to reflect usage leading up to the last few days. Citations are the number of other articles citing this article, calculated by Crossref and updated daily.
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In this study, we analyze the influence of the pore structure of an SBA particle on the light emission from its inner adsorbed quantum dots QDs and outer light-emitting diode LED chips. It is found that the particle features of a high refractive index, comparable feature size of pore structure, and lower amount of QD adsorption help with QD light extraction, demonstrating a mechanism to suppress QD light propagating through pores and thus reducing the reabsorption loss.
The LEDs demonstrated a record luminous efficacy the ratio of luminous flux to electrical power of These results are comparable to conventional phosphor-based white LEDs, which can be a starting point for white LEDs only using QDs as convertors toward commercialization in the near future. The American Chemical Society holds a copyright ownership interest in any copyrightable Supporting Information.
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Since LEDs are inevitable in our lives, it is a good idea for the interested folks engineers, driver designers etc. This article is composed as a brief understanding guide to LED which include a brief introduction, the electrical symbol of LED, types, construction, characteristics, LED Drivers and many.
The most common eminent source of light available in electronic components are Light Emitting Diodes. For instance, they are widely used for displaying the time and many other types of data on screens in certain display devices.
It has the major advantage of low manufacturing cost and renders longer life than the laser diode. A light emitting diode consists of two principal elements of semiconductor. They are positively charged P-type holes and negatively charged N-type electrons. When the positive P side of the diode is connected to power supply, and N side to the ground, then the connection is said to be in forward bias which allows the electric current to flow through the diode. The majority and minority charge carriers of P side and N side combine with each other and neutralize the charge carriers in the depletion layer at the PN junction.
Light Emitting Diodes
The migration of electrons and holes in turn releases some amount of photons which discharges energy in the form of monochromatic light at a constant wavelength usually in nm, which resembles the color of an LED. The color spectrum of LED emission is typically extremely narrow. In general, it can be specified as a certain specific range of wavelengths in the electromagnetic spectrum.
The selection of emission of color from the LED is fairly limited due to the nature of semiconductor used in the manufacture. Commonly available colours of LED are red, green, blue, yellow, amber and white. The light from red, blue and green colours can be easily combined to produce white light with limited brightness.
The working voltage of red, green, amber and yellow colors is around 1. The actual range of working voltage of a light emitting diode can be determined by the breakdown voltage of semiconductor material involve in the construction of LED.
It is due to the differences in the energy gap band structure of semiconductor materials and so different number of photons is emitted with varying frequencies. However the wavelength of light depends on the band gap of the semiconductor materials at the junction and the intensity of light depends on the amount of power or energy applied through the diode.
The output wavelength can be maintained by using compound semiconductors, so that required color can be observed, providing the output within the visible range. Light can be produced and controlled by electronic means in a number of ways.It is made of high resistance semiconductor, and very light intensity.
In the dark, there are very few free electrons in the semiconductor. When light strikes the material, photon energies are absorbed and…. LED lights and fiber optic trees are two energy-efficient technologies that can reduce your energy costs, particularly when the lights are used for long periods of time, such as in commercial applications.
Each year sincemanufacturers have improved the choices, producing bigger and brighter bulbs and new color options. LED lights have a number of benefits over conventional…. Characteristics such as transmittance Tabsorption Arefractive index n and extinction coefficient k are also reported. To the American people it meant that now they could drop nuclear warheads on anyone at any given time. Maybe the most important part of the launch of Sputnik was that it showed the United States how behind they were.
After this, Sputnik 2 is launched containing a dog in it to see if a living organism can survive in space. Two months later the United States finally makes it a competition. They send Explorer…. Introduction: In the recent years there has been an increasing interest in the field of organic electronics due to its light-weight, high flexibility, and easy processability. Indium-tin oxide ITO has been widely used as the transparent electrode in flexible devices, but due to its limitation in mechanical flexibility, large use and high cost there is a great….
They are infrared and ultraviolet. Visible light is the type of light that has a wavelength of nm, and can be see by humans…. The development of forgetting youngsters on the bus is one in every of the issues suffered by the kids, that has accrued considerably in recent years.
This has usually light-emitting diode to the death of the many students on account of suffocation owing to the dearth of attention of derivers. This project,…. The questions that are often asked about solar powered lights is how long it can go and how can one prolong the life of solar powered lights as well as ensure they give the best performance. Most of the time, people discover that the quality and performance of their solar lights reduces in a short period. For instance, the light emitted may not be as bright as it used to be.
In addition, if…. When the electrons reach a device such as a light bulb or a TV, the electrons provide these devices with power in order to make them work. Most circuits include a switch in order to turn them on and off.
When the switch is turned off, it creates a gap in the circuit,…. In the article, highly efficient, light-emitting diodes LEDs could slash the world 's electricity consumption, "like cooking, the synthesis requires a 'recipe. Essays Essays FlashCards.
Browse Essays. Home Page Light-emitting diode Light-emitting diode. Page 47 of 50 - About Essays. Read More. Words: - Pages: 9.Please join StudyMode to read the full document. A diode is a basic electronic component that allows electricity to flow one way only.
The discovery of " light emitting " diodes we believe was an accident sometime around when a diode in an early radio transmitter was noticed to glow when in use. Incandescent bulbs use resistance in a filament to impede the flow of electricity, heating up to a degree which emits light. It takes high amounts of energy to do this and the filament burns out in time and high levels of wasted energy are given off in the form of heat.
CFL "energy savers", fluorescent tubes and many other conventional lamps use higher frequency alternating current to excite harmful chemicals to emit light. One 5 foot 1,5meter tube contains enough mercury to contaminate a swimming pool. Billions have been dumped into waste disposal. Heavy metal poisons have a cumulative effect. In the long term these cannot be a "fix" for the energy crisis we face today. They are poisoning our earth and also us directly through the food chain and locally with emission of Calub Marshela Alpha B.
Jayson Antonio Chemistry Department January 04, Abstract The goal of this study is to learn how the colour of light affects photosynthesis, to identify the effects of different coloured lights on plant growth, and to identify the potential use of different light colours as a growth regulator.
An experiment was performed with the help of 7 students. Mustard sprouts were used as the experimental subjects. The current measures of the mustard sprouts and the different colours of cellophanes were the independent variables.
The 20 dependent measures are grouped according to what colour of cellophane was used to cover the box where it is planted. The results of this study showed that the mustard sprouts that were exposed in orange and green lights have slow development while the sprouts under red and blue light showed rapid development.
Therefore, this study strongly suggests that orange and green light should not be used for growing plants under light. On the other hand, in order to obtain the optimum growth or development of the plant, red and blue lights are more efficient to use.
Although the suggested colours of light represents a higher probability of rapid plant growth, it still depends Other purposes of this experiment include calculating the proper current for each LED, measuring the evaporation rate of rubbing alcohol, and being able to discuss the outcome of the relationship in light energy and the color of the light producing the energy. Create a location for applying light from the LED to the drop of alcohol while minimizing the effect of air currents on the evaporation rate, by making a three-sided enclosure with the cardboard box.
Place a single drop of isopropyl rubbing alcohol on an index card within the enclosure using the eyedropper. Try and make sure you are using the same size drops when repeating. Without the LED present, measure the time it takes for the drop to evaporate.
You will notice that the spot on the card from the alcohol will not be visible, and record this evaporation time in an Excel spreadsheet.Our customers realise that this is the best opportunity to sell more premium wines at a healthy profit.
I believe we will continue to see this trend in 2016. Please do take the time to check out the original post which is linked in this article. Michael has been involved in the hospitality and leisure industries internationally at the highest levels as a chef, an operations director, educator, consultant, finance director, business owner, published writer, board member, company director, serial entrepreneur and investor for over 25 years.
Michael is an American adventurer and world traveller, who now lives in London with his wife and children. The small restaurant serves the traditional Vietnamese Pho style food. We have unfinished business here. This city has a well-known magical influence on Muscovites. Espresso Martini Fest, London Aug 10-12 (DrinkUp. Just like our other festivals, all you need to do is grab a. Wait, that would be too embarrassing going back to.
London Mezcal Week, Sept 11-17th (Drinking Trends) We love Mezcal, and so should you. Well besides being the most characterful, most artisanal, and most interesting spirit out there, Mezcal is a whole heap of fun.
In general, only the information that you provide, or the choices you make while visiting a web site, can be stored in a cookie. For example, the site cannot determine your email name unless you choose to type it. Allowing a website to create a cookie does not give that or any other site access to the rest of your computer, and only the site that created the cookie can read it. Since the launch of the Shell Optimax brand in 2001, the use of premium fuels has grown and they now account for a significant part of European fuel sales in selected markets.
Fuel retailers are interested in differentiated fuel offerings. This brief examines the penetration of premium petrol and diesel in key European markets and reviews the major premium fuel providers. An overview of the leading premium fuel brands and their availability, both in terms of site numbers and as a proportion of total company sites.
Premium fuel penetration by market, in volume terms and as a proportion of total petrol and diesel sales. Information on the main promotional activities and marketing campaigns of the key premium fuel retailers. Predictions on the penetration of premium petrol and diesel volumes across selected European fuel markets to 2010.
Although most major oil companies in Europe have a premium fuel offering, the proportion of their service stations selling premium fuel varies. Oil companies have led focused marketing campaigns to encourage the consumption of premium fuels. Marketers do not use the same message for premium petrol and premium diesel. Environmental protection is the core marketing message of premium diesel promotions whilst improved engine care is the core marketing message of premium petrol promotions.
The penetration of premium fuels varies greatly by market. Measure the availability of premium fuel brands across Europe, both in terms of total site numbers and proportion of company sites. Uncover the core marketing messages and channels used by retailers to promote premium fuels.
Learn the extent to which premium petrol and diesel have penetrated the European motor fuel market and relative consumption by market. Introduction Since the launch of the Shell Optimax brand in 2001, the use of premium fuels has grown and they now account for a significant part of European fuel sales in selected markets.
Scope An overview of the leading premium fuel brands and their availability, both in terms of site numbers and as a proportion of total company sites.