The moderator’s objection about the pupil change was definitely in the right direction…
One mechanism that contradicts an argumentation: “natural light is much more intense and therefore cannot damage the retina” is the so-called chemical adaptation. The brighter the light in the environment, the more the visual pigments in the retina decrease. This effect is familiar to everyone who walks out of the sunlight into a dark interior – the eyes need some time to be able to guarantee full orientation again here: they have to slowly get used to the darkness. This is done by building up new visual pigment, which takes some time.
It is therefore valid:
1. The brighter the light, the more visual pigment is broken down, making the eyes less sensitive to light.
2. The darker conditions are, the more visual pigment is formed in order to still be able to navigate even at low light levels.
Why is the visual pigment so important in this observation? This must be formed again and again in the retina, because it becomes “used up” during vision. For this purpose, a cyclic process exists that regenerates the once-used visual pigment over various stages until it is finally available again for a new visual process. The problem here is that the intermediates of the visual pigment form oxygen radicals when they come back into contact with light prematurely. So, on the one hand, visual pigment is the basis of the visual process, but on the other hand, it acts as a photosensitizer that can damage the retina – it makes the retina more sensitive to the harmful effects of high-energy light.
The equations: “much light = high damage” and
“little light = little damage” therefore do not add up in reality. With reference to the laws of chemical adaptation, they must namely read:
“lots of light = low concentration of visual pigment = lower photosensitization = lower damage.”
versus
“low light = high concentration of visual pigment = high photosensitization = higher damage with unfavorable (= blue-heavy) spectral distribution”.
The actual conditions are thus much more complex and are inadequately described by a simple equation of intensity and damage potential. In addition to the wavelengths and intensities of incident light, a risk assessment must include mechanisms such as chemical adaptation and the relationship between damage and repair, as well as the temporal relationships of all mechanisms involved.