Transcript
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
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
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
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