How to read at night (without ruining your sleep)
First off, no reading on your phone or tablet. The blue light from those screens will mess with your sleep.
What if you want to read but don't want to disturb your spouse with a bright light? Then you have 2 choices:
Use an e-reader that allows you to use warm light. The e-ink screens have been shown to affect sleep almost negligibly.
Use a book light that can clip onto your book. I especially like this. You can adjust the brightness, temperature and reading angle easily.
I use 1 and 2 interchangeably depending on the kind of book I'm reading. But if I'm feeling lazy... I just lie down on my side with my Kobo and read one-handed till I fall asleep.