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The LED optical properties and requests

The luminous flux of LED

Due to the human eyes to different wavelengths of the electromagnetic wave with different sensitivity, we can’t directly with the radiation power of the light or radiation flux to measure the light energy, but must be used by the human eyes to light feeling as a benchmark of the unit-luminous flux(Φ), unit(lm). The measurement of LED luminous flux, use the goniophotometer can realize precise measurement. This is the absolute measurement method of LED total luminous flux, also, integrating sphere is used in industrial measurement commonly. The size of the integrating sphere as big as possible, can minimize the error.

Spectral characteristics, chromaticity coordinates, dominant wavelength measurement

According to the international commission on illumination (CIE) three times technical communication and comparison of relevant international as a result: A. National metrology department should adopt double monochromator measurement system; B. Monochromator measurement system can meet the industry applications; C. 1 nm and 5 nm spectral measurement bandwidth’s chromaticity test results are close , can use 5 nm bandwidth measurement; D. The main wavelength measurement comparison difference is small; E. The CCD measuring instrument relative error is bigger.

The requirement of standard LED characteristics

A. Standard LED working temperature generally is higher than the environment temperature, also has a refrigeration technology solutions;B. Standard LED samples ageing needs hundreds of hours,so choose one of the stable as later calibration;C. Standard LED must be with the test sample has the same spectral power distribution,need to establish a variety of different colors standard LED. Especially the white LED,because it can be made of different spectral components,development the general white LED standard almost impossible;D. Standard LED must be with the test sample has the same luminous intensity distribution curve,if the color of the LED (spectrum) under test with the standard LED (spectrum) are different, you have to calibration spectral photometric detector.

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