According to the European Directive 2006/25/EC on Artificial Optical Radiation the employer has to determine the exposure at the workplace. In addition he shall give particular attention, when carrying out the risk assessment, to any indirect effects amongst others such as temporary blinding.

In order to get reliable quantitative data concerning the influence of dazzle, flash-blindness and afterimages it was the goal of this research project to investigate the various parameters which determine the respective impact on vision. Therefore low power laser and high-brightness light emitting diodes (HB-LEDs) have been applied in different specially developed test setups. A total of 191 subjects have been tested in 1,736 trials during the project.

Afterimage durations up to 300 seconds were found if the fovea of the human retina is irradiated during 10 seconds from a laser beam with less than 30 μW. The visual acuity was strongly reduced during about 30 % of the afterimage time.

The time-dependent progression of the afterimage colors was determined as RGB-values for 4 different dominant wavelengths of HB-LEDs, i.e. 455 nm, 530 nm, 590 nm and 625 nm, in the optical power range between 0.05 mW and 0.5 mW for exposure durations between 0.5 s and 5 s.

The color contrast capability after glare from HB-LEDs was investigated with specially developed test color charts. Glare increases the identification times about 16 s and even stronger impairment is observable especially at low color contrast.

Tests with pseudoisochromatic color plates (Ishihara charts) have shown that color vision was impaired for periods between 27 s and 186 s depending on the applied color plate and respective LED color.

Such relatively long lasting visual disturbances could be of particular importance connected with performing safety critical operations such as working with machines or at height, with high voltages or driving a vehicle or an airplane.

Due to the results of the present work we propose to classify light-sources according to their temporary blinding effect into classes B0, B1 and B2. Whereas class B0 means no blinding effect or a dysfunction of vision up to maximum 2 s, class B1 means the dysfunction lasts up to 10 s and class B2 means it lasts longer than 10 s.

Please download the complete report "Dazzle caused by sources of optical radiation" (in German only).