I'm thinking about human perception and particularly the experience of how bright artificial light is. I'm talking about dusk, when the sun has set and only street lamps and light reflecting off clouds provides light. What affects the perception of brightness of ambient artificial light at night?
Let's provide a concrete example: same appartment, same lights outside, but looking outside on one day it looks dark, while on the other day it is much clearer and brighter. What can account for such a difference?
Is there some part of the brain or some mechanism that is responsible for perceiving how "bright" such light is? I know of visual purple that gets produced after prolonged exposure to darkness, and is effective for seeing in the starlight/moonlight. But it appears to me that visual purple is too easily destroyed and may not get produced under streetlight conditions.