I would experiment and see what affected me and what was okay? I use my Nook nightly before bed to read and my bedside light I don't know how much light might be too much for me and what other factors (time I go to bed and time I get up, what I've had to eat and when, medicines I'm taking, etc.) influence it.

Here's an article on the science of lights and sleep: Blue light has a dark side - Harvard Health Publications