That’s why you are awake on the day
Sunlight contains lot of blue light and stimulates the production of hormones by our body glands.
Blue/White light in the evening deludes the brain that it is daytime, which inhibits the production of melatonin,result is difficult to sleep.
This depends by many factors like amount of light,age,sensitivity.
Of course the darkness is the best allied for sleep
A source of light (and heat) natural and primordial that I like at night is the embers.