Brightness too low in Debian Wheezy

I have just installed Debian Wheezy in my Toshiba Laptop and it works great. However, sometimes the brightness level is too low when starting the system. If I use the keys Fn+F6 to decrease and Fn+F7 to increase it, a bar appears in the screen, increasing or decreasing but the brightness level did not change. Do you have any ideas? PS: I'm using the gnome fallback mode.