Mainly laser classification is taken into account when risk assessment is carried out. In this case deterministic potential damage to the eyes is considered. On the other hand indirect effects as a result of glare by laser radiation can lead to dangerous situations, especially for activities that depend on an unrestricted vision. Currently it is required by national and regional regulations that the risks based on temporary blinding must be taken into account. In this context, the duration of a visual impairment is of great importance; however knowledge of exposure limits for disability glare is not widespread.
To determine functional relationships various test setups have been realized, and thus the duration of visual impairment as a function of laser exposure at various wavelengths has been measured experimentally with several subjects. Additional to the laser wavelengths 532 nm and 632.8 nm, LEDs with wavelengths at 455 nm, 520 nm, 530 nm, 590 nm, 593 nm, 625 nm, and 638 nm have been used. For colored LED radiation it was found that the duration of the visual impairment does not depend in the same marmer on the angular subtense and on the size of the apparent source, like in the case of the exposure limit values.
In addition to direct glare from the laser source during the irradiation the vision loss is caused primarily by afterimages, whose intensity and duration depends on various factors. The so-called “flight of colors” of an afterimage and its time decay plays an important role for the visual impairment, but is not simply related in order to directly determine its duration. For this purpose, special eye test tasks, based on a modified Landolt-C visual test or on a reading task, were developed and the visual impairment determined. Additionally the visual task had been modified in order to simulate a task which might occur in a cockpit.
As a key parameter in addition to the optical power, the respective exposure duration was considered. It was found that even relatively low laser powers of a few microwatts and exposure durations even less than a second led to significant vision impairment. The duration of visual impairment can be described as a logarithmic function of the incident optical energy and this enables the derivation of thresholds for glare. The wavelength dependence of impairment of glare is much lower than it could be expected from the well-known CIE standard photopic luminosity function.