Article Abstracts | February 2007
The complete article appears in the February 2007 issue of Photonics Spectra. If you do not have a copy of this issue,
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High-Power LEDs Pose Safety Hazards
Before standards are in place, users must be aware of safety issues and advice.
by Geoff R. Davies, Lucid Optical Services Ltd.
Because LEDs are so often used as indicator lamps on electronic equipment and in low-power lighting applications such as flashlights, Christmas decorations or rear lamps on bicycles, you might think that they are not hazardous to the eyes. However, high-power LEDs have been developed for uses such as streetlights and car headlights, and these certainly can cause retinal damage if used inappropriately.
The output of an LED intended for lighting is usually quoted in lumens. Modern high-power devices, such as the Luxeon K2 line or the Cree Xlamp 7090 XR-E series, can produce more than 100 lm of output from a single LED chip. A typical 100-W bulb produces an optical output of about 1750 lm, however, so why are LEDs more hazardous???
The answer lies in the extremely small size of the emitting region of the LED and, to some extent, the different spectrum of the emitted light. Because the emitting region is small (3 mm
2 in the case of the Luxeon K2, for example), the eye can focus the light to form a small image on the retina with a high power density capable of causing localized damage (Figure 1). This damage can be either photothermal or photochemical...
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