LED or Light Emitting Diode is a PN junction diode, which is specially doped and made of special type of semiconductor, emits light when it is forward biased is called light emitting diode. In other words, a light-emitting diode (LED) is a two-lead semiconductor light source. It is a p–n junction diode, which emits light when activated. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons.
The forward bias Voltage-Current (V-I) curve and the output characteristics curve are shown in the figure above. The V-I curve is practically applicable to burglar alarms. The forward bias of approximately 1 volt is needed to give significant forward current. The second figure is used to represent a radiant power-forward current curve. The output power produced is very small and thus the efficiency in electrical-to-radiant energy conversion is very less.
The commercially used LED‘s have a typical voltage drop of 1.5 Volt to 2.5 Volt or current between 10 to 50 milliamperes. The exact voltage drop depends on the LED current, colour, tolerance, and so on.
The P-N junction can convert absorbed light energy into a proportional electric current. The same process is reversed here (i.e. the P-N junction emits light when electrical energy is applied to it). This phenomenon is generally called, which can be defined as the emission of light from a under the influence of an . The charge carriers recombine in a forward-biased P-N junction as the electrons cross from the N-region and recombine with the holes existing in the P-region.
Free electrons are in theof energy levels, while holes are in the valence . Thus the energy level of the holes will be lesser than the energy levels of the electrons. Some portion of the energy must be dissipated in order to recombine the electrons and the holes. This energy is emitted in the form of heat and light.
The electrons dissipate energy in the form of heat for silicon and germanium diodes but in(GaAsP) and (GaP) semiconductors, the electrons dissipate energy by emitting . If the semiconductor is translucent, the junction becomes the source of light as it is emitted, thus becoming a light-emitting diode, but when the junction is reverse biased no light will be produced by the LED and, on the contrary, the device may also be damaged.
Advantages Of LED-
There are many advantages of using a LED as :
- It helps in saving energy.
- Reduction in costs.
- Self Ambience Adjustment.
- Soothes & Energizes the environment & People.
- Enhances the brand with its gorgeous lighting.
- Environment Transformation.
Disadvantages Of LED-
The colour of white LEDs can be very inconsistent, although manufacturers have narrowed their binning ranges. White LEDs with the same correlated colour temperature can have different colour tints perceptible to the human eye.
Fabricating LEDs is a complex high-temperature process involving the growth of crystalline layers across the surface of a semiconductor wafer. The quality of these layers determines the properties of the LED. Reproducibility is difficult to achieve across a single wafer, or from wafer to wafer, or from day to day. Some LEDs processed from a wafer will yield high-quality devices, while others from the same wafer will have much lower quality and will end up in low-end applications such as children’s toys.
LEDs open up many new design options, some of which were previously inconceivable.
LEDs do not contain mercury and in many cases steps are being taken to replace lead-containing solders (used mainly to fix LEDs to circuit boards) with the lead-free material, in line with European directives. The energy-efficient nature of LEDs also makes them environmentally friendly.
LEDs are low-voltage light sources, generally requiring a constant DC voltage or current to operate optimally. Designing and implementing an effective driver is key to obtain all the benefits of LEDs.
In general, there is a gap in understanding between the LED manufacturers and the lighting community. The former group do not include the latter in their product development activities and do not provide information that is directly comparable to the information available for competing for light sources. The latter do not understand a huge amount about LEDs and are unfamiliar with crucial issues such as thermal management, or why white LED performance is not highly consistent.