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02/06/2011

LED light

 

In June 2008, scientists at the National Institute of Standards and Technology (NIST) announced the first two standards for solid-state lighting in the United States. These standards detail the color specifications of LED lamps and LED light fixtures, and the test methods that producers should use when testing these solid-state lighting products for total light output,LED Ceiling Light energy use, and chromaticity or color quality.

The Illuminating Engineering Society of North America (IESNA) published a documentary standard LM-79, which describes the methods for testing solid-state lighting products for their light output (lumens), energy efficiency (lumens per watt) and chromaticity.

The solid-state lights being studied are intended for general illumination, but white lights used today vary greatly in chromaticity, or specific shade of white.LED flood light The American National Standards Institute (ANSI) published the standard C78.377-2008, which specifies the recommended color ranges for solid-state lighting products using cool to warm white LEDs with various correlated color temperatures.

Many LED semiconductor chips are potted in clear or colored molded plastic shells. The plastic shell has three purposes:
  Mounting the semiconductor chip in devices is easier to accomplish.
  The tiny fragile electrical wiring is physically supported and protected from damage
  The plastic acts as a refractive intermediary between the relatively high-index semiconductor and low-index open air.

The third feature helps to boost the light emission from the semiconductor by acting as a diffusing lens, allowing light to be emitted at a much higher angle of incidence from the light cone,LED spot light than the bare chip is able to emit alone.


  First application of LED light emitting semiconductor PN junction theory LED light source made of 60 came in the late 20th century. Use at the time of the material is GaAsP, red light (λ p = 650nm), the drive current of 20 mA, the luminous flux is only a few lumens per thousand, and the corresponding luminous efficiency of about 0.1 lumens / watt. The mid-70s, the introduction of elements of In and N,LED strip lightthe LED produces green light (λ p = 555nm), yellow (λ p = 590nm) and orange light (λ p = 610nm), luminous efficiency is also increased to 1 lumen / watt.

To the early 80s, there's GaAlAs LED light source, so red LED light efficiency of 10 lumens / watt. Early 90s, red light, yellow light GaAlInP and hair green and blue GaInN successful development of two new materials to make LED light effect has been greatly improved. In 2000, the former is made of LED tube light  in red, orange area (λ p = 615nm) of the luminous efficiency of 100 lm / W, which made the green LED in the region (λ p = 530nm) of the luminous efficiency can reach 50 lumens / watt.
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