LED light attenuation is the light weakens during transmission, the light fades of LED made by each companies are different, there are light decay also for high-power LED, and it’s have direct relationship with temperature, mainly depend on the chip, phosphor and packaging technology. The LED luminosity attenuation (including luminous flux attenuation, color change, etc.), is a measure standard of the LED quality, also it is great concern to many LED manufacturers and LED user.
According to the lifespan definition for the LED product of the LED industry, the lifetime of LED is the cumulative work time from initial value till light fades to 50% of the original value. This means that the LED still bright when LED achieves its end life time. However, in illumination the light is not allowed if the light output attenuation on its 50%. Typically, indoor lighting the light decay cannot greater than 20%, outdoor lighting fades is not allowed greater than 30%.
At present, the white LED light attenuation is one of the most important issues for it’s enter the civilian lighting market. And manufacturers generally tested attenuation in three ways:
1) Visual method: continuously lit LED, observe the brightness and color changes by human eyes.
2) Use light color testing instrument: that during continuously lit LED process, take the LED into the light color test instrument frequently, and record test results, and report test results by EXCEL or other tools.
3) Use professional testing instruments to measure the light fades, that is put the LED in the test equipment, during the continuously lit, the system will have real-time tracking for the LED brightness and color change, automatically generate information sheet.
--- Extracted from LEDNEWS.ORG