While some types of light promote healing, in general light messes up our sleep patterns. But for some, darkness is frightening and/or has a strong negative
association (maybe with past events)...just guessing, & it's probably none of our business.
Speaking of messing up our sleep patterns, I work nights so I sleep during the day and my snakes are in my room with lights during that time, I had to get a sleep mask so I could enjoy darkness lol.