Screen dimming saves battery

After doing a few tests to determine what was normal, the first power saving technique I wanted to measure was dimming the screen.

My baseline test is unplugging a fully charged 12" Powerbook G4 1.5ghz and seeing how long it stays awake before being forced into sleep mode. In this test, the screen saver is disabled, shutting off the screen is disabled, going into sleep mode is disabled, and there are no active processes running.

With the screen brightness at full, the PowerBook lasts 3 hours, 55 minutes.

Controlling screen brightness is easy to do with the F1 / F2 keys. During meetings I've been dimming the screen to save battery, and I wanted to know if this was making a real difference or not.

Turns out it is: With the screen dimmed (still illuminated, so one click up from the lowest setting), the PowerBook lasts 5 hours, 8 minutes, 31% longer.

Given this, a new power saving setting seems to be in order: One that would gradually dim the screen over a period of a minute or so, and bring it back up when you start using the PowerBook. This would be useful because in meetings, a lot of the times you're just following along in a document, so you need the screen to be visible, but you're not interacting with it much.

Is there a utility that does this already?