ASPECTS AND IMPAIRMENT OF VISUAL FUNCTIONS AS A RESULT OF TEMPORARY BLINDING FROM HIGH BRIGHTNESS LEDS

摘要

Risk assessment in the case of LEDs means that besides compliance with the specified exposure limit values a consideration of indirect effects like temporary blinding has to be performed.Modern high brightness LEDs (HB-LEDs) are capable to produce glare, dazzling effects and afterimages in the human eye. It was therefore the goal of the investigations to determine the different effects associated with afterimages and identify functional dependencies between the applied light intensity and various visual functions.Red, amber, green, royal blue and white high-brightness LEDs (HB-LEDs) have been applied as glare sources. The optical power was restricted to about 4 mW in a 7 mm aperture whereas the exposure duration was between 0,5 s and 20 s, depending on the different methods and test procedures. A total of 90 volunteers took part in the investigations and 935 irradiations have been evaluated.It was found that the size of an afterimage on the retina as a function of time stays nearly constant during relatively long times. Visual acuity and the capability to read a text after an irradiation with a high-brightness LED recovers within 15 up to 60 seconds. A dose-relationship between the applied optical energy and the visual acuity time holds.In addition the so-called "flight-of-colors", i.e. the colored afterimages were determined and recorded in a chromaticity diagram and as RGB-values. Color and contrast sensitivity as a result of colored afterimages due to glare have been measured with the aid of an especially developed test chart based on the Pelli-Robson chart where instead of Sloan letters colored Landolt C-rings were used. Visual impairment durations up to about 3 minutes have been measured as far as color vision is concerned and the influence of the color of the applied LED on the respective colors of 4 different Ishihara test charts was determined quantitatively.