Quote Originally Posted by Jonathan R View Post
This is probably just a stupid question, but I guess it's best to be sure. I'm just about to paint the walls of my new darkroom. It occurs to me that Brilliant White contains optical brighteners. As far as I understand, these are basically fluorescent materials that absorb energy at UV wavelengths and re-emit it within the visible range of wavelengths. Since amber/red safelights are at the other end of the visible spectrum, can I safely assume that these optical brighteners are 'safe' in a darkroom?
Fluorescence always works down the frequency ladder (i.e. from higher to lower energy). UV can cause visible light fluorescence, visible light can cause infrared fluorescence etc. But not the other way round. There is no danger of red or green light becoming blue or UV in fluorescence. Since fluorescence is a quantum process, the energy state cannot be raised. Hope that puts your mind at ease.