A version responses including the natural blink reflex were the main physiological protective measures in laser safety philosophy in the various standards, in which LEDs are included, since several years.
Therefore investigations have been performed in lab and field trials with high-brightness blue (468 nm), red (615 nm) and phosphor-converted (pc) white LEDs applied as single diodes or arranged as clusters (arrays with up to 80 single emitters) with output powers between 0.59 mW and 7.1 mW as extended sources with various virtual source sizes with an exposure duration of 125 ms or 250 ms.
A web cam with a frame rate of 25 Hz was used for the video documentation and subsequent evaluation of the obtained results.
Up to now a total of 2,250 volunteers have been irradiated with a laser beam (1,798) or an LED (452) in order to stimulate the blink reflex and 796 to register aversion responses.
A closer look on the various test procedures, beam geometries, i.e., collimated or divergent, type and location of stimulation (in the fovea centralis or parafoveolar/extramacular), point source or large extended source, shows that a central macular stimulation succeeds in a much higher rate of blink reflex reactions compared to the extramacular case. But compared with a stimulation performed with an LED the frequency obtained with laser irradiation is much lower.
In the case of a white light LED array the frequency of the blink reflex amounts to even more than 50 %, which is much closer to the one reported for a conventional camera flash. The results were surprising in the first moment since the applied LEDs belonged merely to the upper limit of the class 1 according to IEC 60825-1. The higher rate of stimulation might be explained by the much larger area which is irradiated and by the different spectra in the case of an LED application as well. Anyhow a clear psychophysical relationship according to the Stevens power law was obtained and it can be stated that the human eyes are much more protected against radiation from LEDs compared to those from lasers.