WHAT IS AN LED/ BASIC WORKING PRINCIPLE
A light-emitting diode (LED) is a special type of semiconductor device that emits visible light when an electric current passes through it. It has two sides – one with an abundance of electrons called “n-type semiconductor” & the other with bunch of holes that need to be filled by electrons known as “p-type semiconductor “. With the help of these p-n junctions, these semiconductors can control the direction of the flow of electricity. The LED works on the principle that when electrons lose energy, they move from a higher orbit to a lower orbit. The energy lost is in the form of light photons. The color of the light emitted depends upon the frequency of the light photon released. The higher the frequency, the greater is the energy release. Gallium nitride is the light emitting ingredient in LEDs. It is used in the sapphire-based blue and green LEDs. Its practical application is in traffic signals & in lasers in high-definition DVD players.
H. J. Round of Marconi Labs discovered Electroluminescence as a phenomenon in 1907. Later in 1955, Rubin Braunstein of the Radio Corporation of America reported on infrared emission from gallium arsenide (GaAs) and other semiconductor. Nick Holonyak can be called the “father of the light-emitting diode”. He developed the first practical visible-spectrum (red) LED in 1962, while working at General Electric Company.
- Uniform Lighting – the light is spread evenly over the lens which make them brighter than normal luminous lights.
- Energy Efficient – In contrast to the normal lights where a higher percentage of energy is lost as heat, LED light gives off negligible amount of heat so a higher amount of electricity is converted into light. This phenomenon of release of light is known as “electroluminescence”.
- Longer Life – These lights have greater durability & hence are more reliable. They can function for decades, if properly installed.
- Small Size
- No Filtration Required – Unlike Incandescent lamps producing only white light which needs to be filtered for applications such as traffic lights, the light generated by LEDs, need not to be filtered. Thus there is no additional loss of energy.
- LCD panel backlighting - white LEDs are used in flat-panel computer displays.
- Remote Controls of televisions, DVD players, and other domestic appliances – Infrared LEDs are used here.
- Automotive Lighting – LEDs are used particularly in brake lights, turning signals & indicators.
- Traffic Signals – Groups of LEDs are packaged into arrays & arranged to form a traffic light.
- Aviation Lighting
CHALLENGES – Some of the electricity in an LED becomes heat rather than light. If that heat is not removed, the LEDs run at high temperatures, which not only lowers their efficiency, but also makes the LED more dangerous and less reliable. Thus, thermal management of high power LEDs is a crucial area of research and development.
TYPES OF LEDs
Different color LEDs require different forward voltages to operate. Red LEDs require the least voltage, while blue requires higher voltage. Typically, a red LED requires about 2 volts, while blue LEDs require around 4 volts. Based on the color of LED, it can be divided into:
- Visible LEDs – The colors emitted by LEDs various with the temperatures & currents. Different colors are given off at different temperatures & current. LED colors are often given in “nm”, or nanometers, which is the wavelength of the light. LEDs are not perfectly monochromatic, but rather produce wavelengths over a small region of the spectrum.
- Infrared LEDs – are sometimes called IREDs – Infra Red Emitting Diodes. The infrared band can be divided into Near Infrared (NIR) and Far Infrared (IR). Far infrared does not come in the range of LEDs. NIR can be further divided into two bands, longwave and shortwave NIR.
- Ultraviolet LEDs – LEDs emit UV-A which is 400 nm of wavelength. Ultraviolet UV-B causes sunburns, UV-C is dangerous as it kills things. However it is advisable not to stare into an ultraviolet LED.
- White LEDs – have a color temperature. Color Temperature is a measure of the relative amounts of red or blue – higher color temperatures have more blue.
LEDs are created on a substrate of sapphire & hence are expensive. However, a technique is developed to create LEDs on low-cost, metal-coated silicon wafers. The sapphire-based technology, however, is currently too expensive for widespread domestic-lighting use, costing at least 20 times more than conventional incandescent and compact fluorescent light bulbs. China with its low production cost & labor cost has made the manufacturing of LEDs very cheap & affordable.There are LED bulbs on the market which can replace the regular CFLs,the cost has fallen rapidly to around $20.With major Chinese makers getting into the manufacture of the sapphire substrates and wafres,it is expected that the general lighting market will be completely taken over by LEDs.