I was using my mac without my external monitor, and went to adjust the brightness when it got dark only half way down. The first picture is the lowest I can go before the screen goes black. The second picture is how high I have to go before the screen turns back on.
First Pic: http://imgur.com/OKgx9b6
Second Pic: http://imgur.com/shYx0wg
First Pic: http://imgur.com/OKgx9b6
Second Pic: http://imgur.com/shYx0wg