cabin lights are dimmed at night to allow those who want to sleep an easier time of it...you have your own reading light above you to use at your discretion
the window shades are usually pulled down after landing and as you park during the day in hot weather to aid in keeping the plane's interior cool.
it takes almost 45 minutes to obtain ''night vision'' after lights go out, so it really doesn't matter for takeoff asyou are well under the 45 minutes.