I've been frustrated flying at night with the iPad display because it's just too bright - it is almost blinding in a dark cockpit. So I went looking for some sort of a screen protector or some sort of light filter that I could put over the iPad screen at night to dim it further than the stock lowest setting.
What I found was the following iPad/iPhone setup "trick". It worked great tonight with the lights off/dark room. I don't think it will be perfect but it's definitely a big improvement over the stock slider settings.
http://www.techrepublic.com/article/pro-tip-dim-your-ios-screen-with-an-accessibility-setting-trick/
Dave