White led

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

7. 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

8. 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

9. 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

10. 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

11. 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

12. Applications Street and outdoor lighting Architectural lightning Down lights Freezer case lighting Retail display lighting Horticulture lighting Portable lighting

13. References Driving 21 st 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/articles/advances-in-led-thermal-management.html