sorry for this stupid reply.. but please bear in mind that the light on the backside of your phone is suposed to be a flashlight for photos!
some older phones and android 1.6 phones had an hardware lock that turned of the light if it had been working for more than 30 seconds or 1 minute (as a savetylock). newer phones have been found with the same problem (can't confirm you phone to be one of them). some people left the lock for what it was letting the torchapp function weird or fc.. some roms (like CM7) have a workaround programmed...