3. Introduction:
• The Light-emitting
diode is a p-n
junction diode.
• It is a specially
doped diode and
made up of a
special type of
semiconductor.
• When light emits in
the forward biased
then it is called light-
emitting diode.
4. Working principle:
• When current
flows across a
diode.
• Negative
electrons move
one way and
positive holes
move the other
way.
5. Working principle :
• The holes exist at
the lower energy
level than the
free electrons.
• Therefore when
a free electron
falls it losses
energy.
6. Working principle :
• This energy is
emitted in the
form of a photon,
which causes light.
• The colour of the
light is determined
by the fall of the
electron and hence
energy level of the
photon.
7.
8. Types of LED :
• Galliun Arsenide(GaAs) – infra-red.
• Gallium Arsenide Phosphide(GaAsP) –
red to infra-red, orange.
• Aluminium Gallium Arsenide
Phosphide (AlGaAsP) – high brightness
red, orange-red, orange and yellow.
• Gallium Phosphide(GaP) – red, yellow
and green.
• Aluminium Gallium phosphide(AlGaP)
– green.
10. Uses of LED:
• LEDs are used as a bulb in the homes
and industries.
• LEDs are used in bikes and cars.
• LEDs are used as flash in mobile
phones.
• LEDs are used at the traffic light
signals.
• LEDs are used as fast-speed switches.
• LEDs are rapidly replacing cathode ray
tubes in solid-state video displays.
12. Advantages:
Efficiency:
LEDs emit more lumens per watt than
incandescent light bulbs. The efficiency of LED
light is not affected by shape and size.
Color:
LEDs can emit light of an intended color
without using any color filter as
traditional lighting methods need.
Size:
LEDs can be very small (smaller than 2mm
sq.) and are easily attached to printed
circuit board.
13. Disadvantages :
Initial price:
LEDs are currently slightly more
expensive (per lumen watt).
Temperature dependence:
LED performance largly depends on the ambient
temperature of the operating environment or
thermal management properties.
Impact on insects:
LEDs are much more attractive to insects than
sodium-vapor lights, so that there has been
speculative concern about the posibility of
dispurtion of food webs.
