There's an app called Screen Filter that dims it even more. I can't remember what post it was, but some people were dimming too much - something about a dark closet to get it bright enoughto use. I don't remember if it was Screen Filter or some other program to dim the screen. Just remember not to go too dim.
Edit: here's the post about the dark closet.
https://www.mobileread.com/forums/sho...=screen+filter