Visible LEDs and invisible LEDs are two classes of light emitting diodes. The wavelength or color of emitting light depends on the forbidden gap or energy gap of the materials. Types of LED :
- Gallium Phosphide (GaP) – red, yellow and green
- Aluminium Gallium Phosphide (AlGaP) – green
- Gallium Nitride (GaN) – green, emerald green
- Gallium Arsenide (GaAs) – infrared
- Gallium Arsenide Phosphide (GaAsP) – red to infrared, orange
- Aluminium Gallium Arsenide Phosphide (AlGaAsP) – high-brightness red, orange-red, orange, and yellow
- Gallium Indium Nitride (GaInN) – near ultraviolet, bluish-green and blue
- Silicon Carbide (SiC) – blue as a substrate
- Zinc Selenide (ZnSe) – blue
Applications of LED :
- Picture phones and digital watches
- Camera flashes and automotive heat lamps
- Aviation lighting
- Digital computers and calculators
- Traffic signals and Burglar alarms systems
- Microprocessors and multiplexers
- Optical Communication
- Indicator lamps in electric equipment
- LED television
- Vehicle head lamps, domestic and decorative illumination, street lighting.
Advantages of LED :
- LEDs operate very fast.
- These can emit different colors of light.
- LEDs do not contain toxic material like mercury which is used in fluorescent lamps.
- Brightness of LED can be easily controlled by varying the current.
- These are smaller in size, light in weight and have longer in lifetime.
- These are very cheap, readily available and consume low energy.
- Almost no warm up period. LEDs start emitting light in nanoseconds.
- Excellent colour rendering: Colours produced by LED do not fade out making them perfect for displays and retail applications.
- Environment friendly: LEDs do not contain mercury or other hazardous substances.
- Controllable: Brightness and colour of light emitted by LEDs can be controlled.
Disadvantages of LED :
- LEDs are efficiency is low and need more power to operate than normal p-n junction diodes.
- Hazardous blue light quality, temperature dependence, voltage sensitivity, high initial cost.
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