This document summarizes LED (light-emitting diode) technology. It begins with an introduction defining an LED as a specially doped semiconductor p-n junction diode that emits light when forward biased. The working principle is then explained as current flowing across the diode, causing negative electrons and positive holes to move in opposite directions. When an electron falls to a lower energy level, it releases energy in the form of a photon, producing light. Different semiconductor materials produce different colors of light. Common uses of LEDs include lights, displays, traffic signals and electronics. Advantages are high efficiency and small size, while disadvantages include higher initial costs and temperature dependence.
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.
