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Product Code: ILSC2009_204

Comparison of Afterimage Formation and Temporary Visual Acuity Disturbance after Exposure with Relatively Low Irradiance Levels of Laser and LED Light
Authors:
Hans-Dieter Reidenbach, Cologne University of Applied Sciences ; Koeln Germany
Presented at ILSC 2009

The employer in the European Union has to determine in a risk assessment according to the European Directive on Artificial Optical Radiation whether workers might be exposed above the exposure limit values, which are based on the respective ICNIRP guidelines. In addition, he shall give particular attention to any indirect effects amongst others such as temporary blinding.
In order to obtain more information on transient effects, which are the result of interaction of visible optical radiation with the human eye and have an impact on the visual cortex, we have investigated the capabilities to produce such visual interferences due to artificial sources, especially laser and high-brightness LEDs.
It is well-known that dazzle, flash-blindness and afterimages may be caused by bright visible optical radiation, but functional relations are not a matter of common knowledge up to now.
Due to the fact that laser products which belong to Class 2 according to edition 2 of the parent international laser safety standard, IEC 60825-1, imply a time base of 0.25 s which is inherent in the definition of this class, the main interest in the investigations has been in Laser Class 1 and LEDs of the so-called exempt group in compliance with the dual IEC/CIE logo standard IEC 62471 Ed. 1. Intrabeam viewing of Class 1 laser products which emit visible radiant energy is regarded in the laser safety standard to be capable to produce dazzling visual effects, particularly in low ambient light, whereas there is not even a hint concerning physiological glare effects as far as LEDS belong to the exempt and low risk group in the lamp standard. Up to now the philosophical basis for the Risk Group 2 (Moderate-Risk) classification is that the lamp does not pose a hazard due to the aversion response to very bright light sources. But on the other hand it has been shown convincingly and reported that it is not true for LEDs and even LED arrays in any case that this requirement is met by any lamp that exceeds the limits for Risk Group 1.
Since there exist several work areas and places where it might become very important not be impaired to much as far as visual acuity, contrast sensitivity and color vision are concerned, like working with machines or at height, with high voltages, driving a vehicle or flying an aircraft, it was the goal of the investigations to determine the most important relationships and to compare laser and LEDs.
In detail 2 different laser devices, namely a helium-neon laser (632.8 nm), and a frequency-doubled Nd:Yttrium-Vanadat laser (532 nm) as well as 7 different LEDs (red, amber, green, cyan, blue, royal blue, and white) have been applied. The maximum power levels which have been used were kept a factor of 20 percent below the maximum permissible exposure limits in the case of laser radiation and a factor of 8 up to 20 as far as LED-radiation is concerned. A total of 27 persons have been tested with LEDs and 19 with laser light. The exposure duration was chosen at several values between 0.25 s and 10 s and various power levels. The resulting temporary impairment was determined either with a standard visual acuity measuring system or in a specially developed computer-assisted reading test. The quantitative results as a function of wavelengths, optical power and energy will be reported and special attention is given to the determination of threshold values.
The received functional interdependencies might be used for the derivation of protection limits as far as indirect effects like temporary blinding are concerned.

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