Local susceptibility of the retina, formation and duration of afterimages in the case of Class 1 laser products, and disability glare arising from high-brightness light emitting diodes

According to the new European Directive on Artificial Optical Radiation, the employer has to determine the exposure and the assessment of risks and in addition, he shall give particular attention to any indirect effects, such as temporary blinding, when carrying out the risk assessment. Up to now, secondary effects such as temporary blinding have not been regarded in safety standards and there exist but a few data on this topic as far as modern artificial high-brightness (HB) light sources are concerned. Temporary blinding from a Class 1 laser and a white high-brightness light emitting diode (LED) in the visual field has been investigated as a function of the glare angle and of the amount of the emitted optical energy. In an extensive study with a He-Ne laser at a wavelength of 632.8 nm, it was found that even for output powers of 5 to 30 μW, the tested subjects reported intense glare effects and felt uncomfortable due to the high brightness. The durations of afterimages ranged up to 300 s and have been measured as a function of the angle between the line of sight and the laser beam direction for an exposure duration up to 10 s. The maximum afterimage duration was found for the foveal pit. In the case of a HB-LED, the investigated power level was between 0.0045 and 3.96 mW measured in a 7 mm aperture, and the exposure durations were limited to 20 s. The annoyance duration, i.e., the capability to read after an irradiation, was between about 10 and 25 s and relatively independent of the applied power, but interindividually different. As a result of the investigations instructions for users of Class 1 lasers and HB-LEDs should be given in order to take into account temporary impairment of visual tasks due to dazzling and glare effects which are accompanied with relatively long lasting afterimages.