White led has a lot of advantage now n filed of lighting, Here is a small demonstration how the complete system works.

2.  Introduction
 Working of LED
 How is white LED
light made with LED
 White LED structure
 Application
 Advantages
 Disadvantages
 Conclusion

3.  Light emitting diode known as LED in the electronic
industry are poised to replace all conventional light
sources .The LED is simply a semiconductor diode that
emits light when an electric current is passed through
it.
 It is fourth and latest generation of light sources.
 The white LED lamp is equivalent to 60watt
incondescent bulb in size and brightness but lasts 25
times longer and runs on less than 10watts.

4.  The LED is a semiconductor diode that emits
light when current passes through it.
 The n-side is heavily doped.
 When forward biased the built-in potential at
the junction is reduced
 The e- from n-side get injected into p-side
 The e- combine with the holes resulting in
emission of photons I,e light
 This effect is called electroluminescence.

5. Now a time there are two ways of making white LED
1.MIXED COLOUR LIGHT
When red ,blue and green LED located adjacent to one
another and the amount of their out put mixed
properly the resultant light is white.
2.USING BLUE LED WITH PHOSPHOR COATING
When we incorporate the phosphor in the body of a
blue led with a peak wavelength around 450to470
nanometers some of the blue light will become yellow
and some will mix with that yellow light will become
white.

6. MIXED COLOUR WHITE
LED
PHOSPHOR COATED BLUE
LED

8.  Street and outdoor lighting
 Freezer case lighting
 Landscape ,market
,decoration , lawn ,home ,
public places lighting etc.
 Back light in cell phones,
computer , electronics etc.
 Special lighting and military
use
 It is also applied in toys ,
gifts , flash light etc.

9.  Small in size
 Longer life time compare to other
electric source
 Do not contain toxic materials such as
mercury
 Radiated very little heat
 Good stability

10.  White LED prices are higher than that of
incandescent bulb
 Temperature dependent
 Cause more light pollution than other
light sources
 Under cool white LED illumination the
colour of the objects is perceived
differently

11.  Given the remarkable technological
innovation of past few year and it is
expected that the marketing expectation
and the public requirement will increase and
the cost of the white LED will decrease . In the
other hand the range of uses of LED will
increase within the context of saving energy
and the need for thinner designs .