2. Introduction
Led is going to revolutionize the lighting technology within the
next few years
Led lamp is the fourth and latest generation of light sources
Incandescent bulbs
Fluorescent bulbs
High intensity discharge(HID) lamps
The white LED lamp is equivalent to 60 watt incandescent bulb
in size and brightness but lasts 25 times longer and runs on
less than 10 watts
4. The Electroluminescence effect
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
e- combine with the holes resulting in emission of
photons i.e. light
This effect is called electroluminescence
8. Generation methods of white light
RGB synthesis
Using Blue LED with phosphor coating
Other methods include growing zinc selenide (ZnSe) on a
ZnSe substrate which simultaneously emitted blue light
from diode and yellow light from substrate
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12. Challenges
Electrical compatibility
LEDs run on dc voltage
To run from mains, miniaturized circuitry that
converts AC to DC is provided between supply and device
Thermal management
Heat sinks
Fans for cooling
Graphite foam
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14. Basic parameters
Efficacy 80-160 lm/watt
Input power 2-100 watts
Colour rendering index (CRI) 65-97
Correlated colour temperature 2700-8000 k
Life time in hours 50,000 hours
15. Advantages
Small in size
High photoelectric conversion efficiency
Ideal for cycling in lights
Longer life time compared to other light sources
Do not contain toxic materials such as mercury
Can be designed to emit light of intended colour
Radiate very little heat
Can be dimmed
Robust
16. Disadvantages
Exceeds the safety limits of blue-light hazard
Temperature dependent
Causes more light pollution than other light sources
Voltage sensitive
High initial prices
Under cool-white LED illumination, the colour of the
objects is perceived differently
17. Applications
Street and outdoor lighting
Architectural lightning
Down lights
Freezer case lighting
Retail display lighting
Horticulture lighting
Portable lighting