White led

WHITE LED

THE FUTURE LAMP

Introduction

Led is going to revolutionize the lighting technology within the next few years

Led lamp is the fourth and latest generation of light sourcesIncandescent bulbsFluorescent bulbsHigh 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

LED Basics

The Electroluminescence effect

The LED is a semiconductor diode that emits light when current passes through it

The n-side is heavily dopedWhen forward biased, the built-in potential at the

junction is reducedThe e- from n-side get injected into p-side e- combine with the holes resulting in emission of

photons i.e. lightThis effect is called electroluminescence

Colours

The white LED

Generation methods of white light

RGB synthesisUsing 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

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

Basic parameters

Efficacy 80-160 lm/wattInput power 2-100 wattsColour rendering index (CRI) 65-97Correlated colour temperature 2700-8000 kLife time in hours 50,000 hours

Advantages

Small in sizeHigh photoelectric conversion efficiencyIdeal for cycling in lights Longer life time compared to other light sourcesDo not contain toxic materials such as mercuryCan be designed to emit light of intended colourRadiate very little heat Can be dimmed Robust

Disadvantages

Exceeds the safety limits of blue-light hazardTemperature dependentCauses more light pollution than other light sourcesVoltage sensitiveHigh initial pricesUnder cool-white LED illumination, the colour of the

objects is perceived differently

Applications

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

References

Driving 21st century’s lights by Bernie weir , Spectrum, IEEEVolume: 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