Light Emitting Diode
What is Light Emitting Diode(LED)?
A Light Emitting Diode (LED) is a two lead semiconductor light source that emits light when an electric current is applied in the forward direction of the device.
Light emitting diode converts electrical energy in to light energy.
Light emitting diode converts electrical energy in to light energy.
When a fitting voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light is determined by the energy bandgap of the semiconductor.
Structure:
The structure of a Light Emitting Diode is very different from that of a normal signal diode. The PN junction of an LED is surrounded by a transparent, hard plastic epoxy resin hemispherical shaped shell or body which protects the LED from both vibration and shock.
Some indication LEDs have a rectangular or cylindrical shaped construction that has a flat surface on top or their body is shaped into a bar or arrow. Also, nearly all LEDs have their cathode, ( K ) terminal identified by either a notch or flat spot on the body, or by one of the leads being shorter than the other, ( the Anode, A ).
Structure:
The structure of a Light Emitting Diode is very different from that of a normal signal diode. The PN junction of an LED is surrounded by a transparent, hard plastic epoxy resin hemispherical shaped shell or body which protects the LED from both vibration and shock.
Some indication LEDs have a rectangular or cylindrical shaped construction that has a flat surface on top or their body is shaped into a bar or arrow. Also, nearly all LEDs have their cathode, ( K ) terminal identified by either a notch or flat spot on the body, or by one of the leads being shorter than the other, ( the Anode, A ).
Construction and working of LED:
The most important part of a light emitting diode (LED) is the semi-conductor chip located in the center of the bulb .The chip has two regions separated by a junction.
The P region is dominated by positive electric charges ,and the N region is dominated by negative electric charges.The junction acts as a barrier to the flow of electrons between the P and N regions.when sufficient voltage is applied to the semi-conductor chip across the leads of the LED,electrons can move easily in only one direction across the junction between the P and N regions.
In the P region there are many positive than negative charges.Each time an electron recombines with a positive charge,electric potential energy is converted into electromagnetic energy.
For each recombination of a negative and a positive charge,a quantum of electromagnetic energy is emitted in the form of a photon of light with a frequency characteristic of the semi-conductor material.
LED V-I characteristics:
Applications of LED:
The P region is dominated by positive electric charges ,and the N region is dominated by negative electric charges.The junction acts as a barrier to the flow of electrons between the P and N regions.when sufficient voltage is applied to the semi-conductor chip across the leads of the LED,electrons can move easily in only one direction across the junction between the P and N regions.
In the P region there are many positive than negative charges.Each time an electron recombines with a positive charge,electric potential energy is converted into electromagnetic energy.
For each recombination of a negative and a positive charge,a quantum of electromagnetic energy is emitted in the form of a photon of light with a frequency characteristic of the semi-conductor material.
Light Emitting Diode Colours:
| Typical LED Characteristics | |||
| Semiconductor Material |
Wavelength | Colour | VF @ 20mA |
| GaAs | 850-940nm | Infra-Red | 1.2v |
| GaAsP | 630-660nm | Red | 1.8v |
| GaAsP | 605-620nm | Amber | 2.0v |
| GaAsP:N | 585-595nm | Yellow | 2.2v |
| AlGaP | 550-570nm | Green | 3.5v |
| SiC | 430-505nm | Blue | 3.6v |
| GaInN | 450nm | White | 4.0v |
LED V-I characteristics:
Applications of LED:
- Sensor Applications
- Mobile Applications
- Sign Applications
- Automative Uses
- LED Signals
- Illuminations
- Indicators
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