ICNIRP STATEMENT ON LIGHT-EMITTING DIODES (LEDs) AND LASER DIODES: IMPLICATIONS FOR HAZARD ASSESSMENT

BOTH VISIBLE and infrared laser diodes and light-emitting diodes (LEDs, or sometimes referred to as IREDs in the infrared) are widely used in displays and in many home entertainment systems, toys, signal lamps, optical fiber communication, and optical surveillance systems. Collectively these are referred to as diode emitters (DEs). While the higher power laser diodes have routinely been considered to be “eye hazards,” traditional LEDs have been regarded as safe. However, with the recent development of higher power LEDs, there has been an effort to develop LED safety standards. There are a variety of LED types ranging from surface emitters to superluminescent diodes (SLDs). The latter have some characteristics more typical of diode lasers. Questions have therefore arisen as to whether laser or incoherent radiation exposure limits (ELs) should be applied to each type of emitter. Based upon current exposure limits, most LEDs—particularly surface-emitting LEDs—pose no clear hazard to the eye. Current surface-emitting LEDs produce exposure levels at the retina that are less than 1% of the levels that are known to cause retinal injury (WHO 1982; Sliney and Wolbarsht 1980) even when the LEDs are viewed at extremely close distances (e.g., at 10 cm) (Sliney and Wolbarsht 1980). At typical viewing distances of 0.5 to 2 m, the levels are less than 0.1% of retinal injury levels. Even lengthy exposures of the cornea and lens of the eye pose no hazards whatsoever. From a safety standpoint, LEDs have been treated both as lasers (e.g., in IEC standard 60825-1) (IEC 1998; ANSI 1988) and as lamps (CIE 1999; ANSI/IESNA 1996a,b). Because of some confusion relating to the actual risk, ICNIRP organized a panel of experts to review the potential hazards of current DEs. Laser diodes are constructed with miniature resonant cavities with gain, produce a very narrow spectral bandwidth, can generally achieve shorter pulse durations, are not limited in radiance, and can emit much higher radiant powers than LEDs. Light-emitting diodes of low to moderate brightness (luminance) are used in many types of visual displays as indicator lights and many related products. Higher power LEDs and IREDs are used as signal lamps and in a wide variety of domestic and industrial products, and can compete with laser diodes in limited optical communications systems, i.e., in local-area networks (LANs). They are generally not competitive with laser diodes because of different output characteristics. These differences in output characteristics define both their uses and their potential eye hazards. Most current LEDs have very limited radiance and do not pose a clear eye hazard, despite the fact that they have been included in some laser safety standards in the past few years.