system
Given the following post, respond as if you're commenting on Reddit:
human
To what degree, and how, does flash photography harm museum exhibits?

Most museums that I've visited prohibits flash photography, but allows normal photography, in fear that strong light might harm the artifacts some how. How exactly does this work?
gpt
Ultraviolet light or strong visible light will tend to cause pigments to bleach. What is happening on a molecular level is that the light is breaking apart chemical bonds. With UV light you have a situation where a single photon can break such bonds, so there is really no minimum level of acceptable exposure. With visible light the same thing can happen or a two-step process (of separate photons exciting a chemical bond then causing it to break) can occur.

In general though the light from a properly UV-filtered flash is no more harmful to art than the ordinary gallery lighting, but many galleries and museums maintain a ban on flash photography out of an excess of caution.