Backlight! is a free brightness app/widget for Android that allows you to change the screen backlight of your device with a single click. It is an easy-to-use app that offers complete custom brightness levels and even lets you assign it to a gesture or a main dock for easier access.

The app recognizes values fromwith 1 being the darkest and 255 being the brightest. It also supports automatic brightness, and default levels are set at 1, 50, 150, and 255 respectively. You can even enable Auto Brightness by using the letter 'a'. However, it is important to note that Backlight! controls the screen brightness level only and does not adjust the keyboard brightness or other light features of the phone.

It is important to mention that the app may not work on Sense UI devices such as the Hero, and there might be a potential conflict with Juice Defender, which seems to negate any requests from the app to change brightness. If you plan on upgrading the app, don't forget to add/re-add the widgets to the home screen!