Critical parameters of light emitting diodes and their implications on the optical radiation safety limits according to IEC 60825-1 +Amendment 2

Abstract

Radiation power and image size of the source on the viewer's retina (apparent source) determines the hazard for the eye. Following IEC 60825-1, the effective emission limits are dependent on the tabulated accessible emission limits and the assigned measurement conditions—both depending on the source size. In the case of a light emitting diode (LED), this emitting area is not only determined by the chip size but also by the housing—due to built-in lenses, reflectors, and scattering materials. Also the virtual source position will be distorted by the integrated lenses. Since the measurement distance is related to the apparent source, the source's location must be known for the proper classification and hazard assessments of LEDs. As the accompanying measurement instructions of the standard are developed for coherent sources, they do not fully match the peculiarities of LEDs and lead to different interpretations. A comparison of several approaches will be presented. In this context, the sometimes surprising implication of the new “Amendment 2” on the safety limits of LEDs will also be discussed.