The Pronto has a light sensor, which allows you to do lots of great things.

If you set the light sensor to absolute minimum, it disables the backlight from coming on unless you press the backlight button (alternately, if you set it at full the backlight comes on no matter how bright the room is). When you press the button, the backlight stays on for whatever you have it set to and continues to stay on until you let it time out.