Originally Posted by HarryT
Thank you - I had it in my mind that you could turn it all the way off; I'm obviously mistaken.
You can turn it almost off.
In iPad 3 and 4 we can turn it almost all the way off in Main Settings itself but in iPad 1 we can do that only with additional help of readers like PerfectReader that have got real brightness control.
But as already mentioned it is not just about brightness but contrast also, so we can use low brightness in dark room but not to low for comfortable contrast, because there is no separate contrast and gamma control button like with laptops/pc graphic cards.
I use good anti-glare matte protector and PerfectReader for PDFs on iPad 1 and can read on low brightness whole night/day long without problem, but if we use same protector on new iPads it will reduce its resolution considerably to the level of iPad 1, so if unhappy about that we should try crystal clear anti-glare protector instead or no anti-glare at all.
Although reading experience indoors and outdoors on e-ink is better I would still use iPad indoors more frequently.