In general, your body needs a dark room for sleep.
This is connected to your circadian rhythm. During the day, when the sun shines, the light, and especially the blue light, “tells” your brain that it’s a day and you are energized and active.
At night, when you don’t see the blue light anymore (I’m talking about the natural blue light that comes from the Sun), your brain understands that it’s night, you get sleepy and you fall asleep.
That’s why sometimes it’s way harder to fall asleep if you’ve been sitting in front of the PC till late. It is because of the blue light that you are tired but unable to fall asleep.
Blue light comes not only from our computers but also from the lightbulbs. So sleeping with your lights on may make falling asleep harder.
However, just like some people have already said in the previous comments – if you have some kind of phobia, or are afraid of the darkness, I’m pretty sure that falling asleep in the dark will be way harder for you. So you can try using bulbs that emit more yellow light so that it’s both light in the room, but you are not exposed to blue light at night.
On your PC you can try using a, I do too. Mine is called and I’m very happy with it 🙂
I hope my answer was helpful.
Wish you luck 🙂