system
Given the following post, respond as if you're commenting on Reddit:
human
Why do we prefer to sleep in the dark?

I've always wondered this.
gpt
Humans are evolutionarily adapted to sleep at night (when it is dark) and be active during the day (when it is light).  Chemicals that make you sleepy build up in your brain over the day until you go to sleep at night and your brain gets rid of them all.

There is another chemical as well which wakes you up and stimulates you.  It is triggered by bright light (especially blue coloured light) that historically would be only from the Sun (i.e. it's day time and you need to be active not sleeping).  Artificial lighting simulates sunlight which in turn signals to your body that it is day time and not time to sleep.