Writing

This is the protagonist of my rpg-maker project, a chronicler named Rhel.

I was kind of going for a gloomy atmosphere. He's no dark person but there's an invisible threat haunting his dreams and therefore causing slight insomnia so he's up writing at night. Luckily, he's no human, so he doesn't damage his eyesight by doing so. xD

Unfortunately, I'm still not very good with lighting. I wanted him to sit on the wall underneath a window with only the light of the grey moon illuminating his writing, but I didn't quite know how to achieve this impression by painting.
I'd be really glad if someone had a piece of advice for me regarding this.