From the home screen, tap the Menu key.
Scroll to and tap Display.
Tap to uncheck Automatic brightness.
Note: Automatic brightness will attempt to dynamically adjust the brightness depending on the ambient light level.
If Automatic brightness is unchecked, tap and drag the slider to the desired brightness level.
Once finished, tap OK.
Tap Screen timeout.
Tap the desired timeout period.
The backlight settings are now changed.