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 amongst others such as temporary blinding, when carrying out the risk assessment.

Up to now secondary effects like temporary blinding have not been regarded in safety standards and there exist but a few data on this topic as far as modem artificial high intensity light sources are concerned.

Temporary blinding as the result of a dazzling light in the visual field has been investigated together with a class-1 laser and a white high-brightness LED.

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 μW to 30 μW the tested subjects reported intense glare effects and felt uncomfortable due to the high brightness. The durations of after-images extended 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 after-image duration was found for the foveal pit.

In the case of an HB-LED the power level was between 0.0045 mW up to 3.96 mW 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 s and 25 s and relatively independent of the applied power, but inter-individually 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 by relatively long lasting after-images.

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