iPhone 4 screen goes dark if brightness is set to 80%+
I have had my iPhone 4 for over a year now, and suddenly the screen of my iPhone 4 GSM started to go almost totally dark if I set the brightness level higher than around 3/4 of the bar. The touch screens keeps working, I hear the sounds of locking or unlocking it, I can enter the apps, etc. If I press the sleep/wake button I see a flash of the lockscreen but it goes dark in a second. After a few tries of hard-reboot the device pressing both buttons and getting the same dark screen, I tried to set the brightness level lower by "blindly" entering settings, imagining where the brightness control is located and sliding down the bar (all this I did with the screen totally black), somehow I got it and after pressing the sleep button the lockscreen appeared and I was able to see the homescreen again. So I started playing with the brightness control and in fact it happens when I set it to a very bright level, and it works if I don't let go the control, slide it back to the left of the backlight bar, lock the screen and unlock it.
I fully restored the iphone, and tested it without installing any app, and the problem remains. I have read that many people have issues with the proximity sensor, but this doesn't seem to be the case, the sensor actually works fine with the phone app, and this never had happened before.
Do I need to change the LCD or any other part? Any suggestions?
Is this a good question?