LED working function

1. Light Emitting Diode
(LED)
Dr. Pravin Prajapati
[Associate Professor,
EC Dept, ADIT]
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chapter 7 :- LED

2. Major required characteristics of
sources
 Small Size
 Minimum distortion and noise
 Should emit light at wavelength where fiber
has low losses
 Capable of simple signal modulation over a
wide BW.
 Must couple sufficient optical power
 Narrow spectral width
 Stable optical output
 Cheap and reliable.
2

3. It consists of an
encapsulated chip
of semiconductor
diode and a
suitable lens. The
length of the anode
terminal is
deliberately made
longer than the
cathode terminal
for identification.
Construction and Operation:-
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4. Parts of LED

5. Operation:-
 When the diode is made forward biased, the battery supplies
holes into the P region and electrons into the N region. These
holes and electrons supplied by the battery are called as injected
charge carriers. Now injected electrons near the potential barrier
get recombined with the holes which means that the electrons fall
from the higher energy level to the lower energy level.
 When transition occurs energy is radiated out. In case of
ordinary diodes the energy is radiated out in the form of heat. But
in the case of LEDs the photons are radiated out.

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9. LED as Power Indicator

10. LED Brightness

11. LED Specification

12. LED Applications

13. Blown Fuse Indicator

14. High Power LED

15. High Power LED

16. High Power LED

17. High Power LED

18. Light Bulbs vs LED’s
Light Bulbs
Filament
○ Sudden Failure-
Breaks/Burns down
Recent bulbs last up to two
years at ~20 lumens/watt
Fluorescent tubes last about
7500 hrs at ~80 lumens/watt
LED’s
 No filament
○ Gradual Failure-Intensity
decrease over time
 Last from 50,000 to 100,000
hrs (5-10 yrs)
 Recent LED’s (orange,red)
have efficiency of ~100
lumens/watt
 Generate little heat
○ Reduced A/C costs

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