I have my Paperwhite on 12 all the time, except when it is bright enough and I turn the light off. If you are interested in turning the light off, I made a small guide in this post
that does not require a jailbreak.
For the curious: No, this is not how I turn my light off personally. If you look in the thread that above link is in, you can find it in post #63. Be warned, that it is not recommended to do unless you are comfortable with it and understand the risks that are involved. It also requires a jailbreak and usb network. It is much easier and safer to use the non-jailbreak method.