Assessment About Safety Of High-brightness LED

As the rapid development of Light Emitting Diode (LED), its brightness become more and more dazzling, its power become higher and higher. The ocular safety problem when using LED should be paid enough attention. Unfortunately, due to the widely use and rapid progress of LEDs, there is still no such a acknowledged safety standard for LEDs.To predict the hazard done to human eyes by LEDs and assess the level of hazard correctly is significant to human health.After comparing the regulation about LED by ICNIRP IEC and CIE, we decide to assess the safety property of LED by calculating its Accessible Emission Limit (AEL) according to the method of classification defined in IEC 60825-1. In this method, the angular subtense of the apparent source size is the essential quantity for optical hazard assessment.In the research, we use a software called ASAP to simulate the output beam of LEDs at first. We found the divergence angle of the beam changed regularly with the change of the location of the chip or the shape of the LED's package, hence there must be some relationship between the apparent source size and the divergence angle or the diameter of LED. And then the apparent source size is measured by the image formed through lens and received by CCD. The angular subtense is calculated from the apparent source size and the specified most hazardous viewing distance. At last, the AEL of each type of LED is calculated according the formula in IEC60825.Through the data we got, it can be found that the AEL of retinal thermal hazard has a linear relationship with divergence angle and the diameter of LED respectively. The ordinary non high power LEDs will not cause retinal thermal hazard, but they will probably cause retinal photochemical hazard, especially the ones whose spectrum composed mainly by blue rays.