White LEDs will revolutionize lighting in the next few years. They work using electroluminescence, where current passing through a semiconductor diode causes it to emit light. White light can be generated using blue LEDs coated with phosphor, or by combining red, green, and blue LEDs. Challenges include thermal management and electrical compatibility with mains power. Compared to other lights, LEDs have longer lifetimes, lower energy usage, and no toxic materials like mercury. While prices are currently high, LEDs are being used for applications like street lights and retail displays.

1. WHITE LED
THE FUTURE LAMP

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

3. LED Basics

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

5. Colours

6. The white LED

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

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

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

18. References
 Driving 21st century’s lights by Bernie weir ,
Spectrum, IEEE
Volume: 49, Issue: 3
 Led basics--http://ledlight.osram-os.com/knowledge/
 http://www.lighting.philips.co.in/lightcommunity/trends/led/
 http://www.omslighting.com/ledacademy/570/
 Electrical compatibility--
http://ledsmagazine.com/features/3/5/2/
 Thermal management--
http://www.digikey.com/us/en/techzone/lighting/resources/artic
les/advances-in-led-thermal-management.html