LED (Light Emitting Diode), LED is a solid-state semiconductor devices, it can direct the light into electricity. The heart of LED chip is a semiconductor chip is attached to one end of a stent, this end is negative, the other end to connect the positive power supply. And the whole package together chip by epoxy resin. Semiconductor chip is composed of three parts, part of P-type semiconductor, in which the dominant hole inside, the other side of the N-type semiconductor, here is mainly electronic, the middle is usually 1-5 cycles of the quantum well. When the current through the wire act on the chip, the electrons and holes into the quantum wells will be in the quantum well with electron-hole complex, and then will be issued in the form of photon energy, which is the principle of light-emitting LED. The wavelength of light is the color of light is the formation of PN junction by the decision of the materials.
Recent improvements in manufacture have lowered the cost of LEDs, which has expanded their application. The bulbs are now available in clusters, from 2 to 36 bulbs, and are popular especially for battery powered items such as flashlights and headlamps. LEDs are also available in arrays which fit standard AC and DC receptacles, lamps, recessed and track lights.
Benefits:
1) Energy-saving - LEDs use a fraction of the wattage of incandescent bulbs. Batteries will last 10 to 15 times longer than with incandescent bulbs. Also, because these bulbs last for years, energy is saved in maintenance and replacement costs. Many cities in the US are replacing their incandescent traffic lights with LED arrays because the electricity costs can be reduced by 80% or more.
2) Cool - these bulbs do not cause heat build-up; LEDs produce 3.4 btu's/hour, compared to 85 for incandescent bulbs.
3) Long-lasting - LED bulbs last 10 times as long as compact fluorescents, and 133 times longer than typical incandescents.
4) Light for remote areas - because of the low power requirement for LEDs, using solar panels becomes more practical and less expensive than running an electric line or using a generator for lighting.
5) Durable - Since LEDs do not have a filament, they are not damaged under circumstances when a regular incandescent bulb would be broken. Because they are solid, LED bulbs hold up well to jarring and bumping.
Shortcomings:
1) Light Field - LEDs are focused lights, and therefore are best as task specific lighting such as reading lights, desk lamps, night lights, spotlights, security lights, signage lighting, etc. They do not radiate light in 360 degrees as an incandescent does. The light will be bright where you point it towards.
2) Cost - although the cost keeps going down, LEDs are still expensive. A single AC bulb (30 LED), replacing a 25 watt incandescent, may cost about $40.
New designs in LED bulbs are addressing this problem of directional focus. Diffuser lenses with clustered bulbs are becoming more common on the market which is broadening the applications for LED use in the home.
LED Colors:
Green - green is now the preferred color for pilots and the military. The green color is also great for retaining night vision, and it doesn’t erase the red markings on maps and charts.
Red - red is the traditional color for maintaining night vision.
Blue - many people like the blue because it is very easy on the eyes. Blue appears to be a good reading light for elderly eyes. Elderly folks report that they can read under the blue light for hours without eyestrain, compared to severe eyestrain in less than 30 minutes with incandescent lighting.
White - the most popular of the LED colors. It produces a soft white light, without harsh reflection, glare or shadows.
Amber - LED amber bulbs do not attract flying insects, as do ordinary white bulbs. Amber LEDs are used outdoors in areas such as patios and decks where insects flying around lights are a nuisance.
Although LEDs are expensive, the cost is recouped over time and in battery savings. For the AC bulbs and large cluster arrays, the best value comes from commercial use where maintenance and replacement costs are expensive. Traffic lights, for example, are being switched over to LEDs in many cities.
Smaller arrays, such as those in flashlights, headlamps and small task lights are great for specialty and outdoor use. New clustered arrays with various lenses are now available for more residential applications.
