25-08-2017, 09:32 PM
Light Emitting Diode
1360237424-LEDppt.pptx (Size: 1.54 MB / Downloads: 25)
Definition:-
A LED is a transducer which converts electrical energy into light energy.
OR
In essence, we can say that it is a P-N junction solid state semiconductor diode that emits light when a current is applied through the device.
Light Emitting Diode (LED)
1962-First visible LED was made practical
1968 – First economically mass produced LEDs made by Monsanto Corp & Litronix
1972 - HP introduces the HP35 calculator using an LED display
1993 - Nichia Corp produces the first high brightness LED using phosphor conversion to create white light
2009 - European Union bans most incandescent light bulbs
Some Properties:-
LEDs are highly monochromatic, only emitting a single pure colour in a narrow frequency range. The colour emitted from a LED is measured in nanometres.
Most LEDs are produced using gallium-based crystals that differ in one or more additional materials such as phosphorus to produce distinct colours.
The essential portion of the LED is the semiconductor chip.
LEDs are more efficient than ordinary light bulbs.
LEDs can survive shock that often break conventional light bulbs.
Low operating voltage made the LED ideal for battery powered equipment. For eg:- digital watch, calculator etc
Working:-
When we pass current
to LED, electrons from n-type
meet with holes of p-type, in
this meeting electrons falls
into a lower energy level( conduction band to vale-
nce band) and releases energy in form of light.
The wavelength of light emitted, and thus its colour depends on band gap energy of the materials forming the p-n junction.