Screen backlight turns off every 2 seconds

I have noticed, that other people too have problems with the backlight, but mine is a bit different.

When i tap the screen brighter once it goes to the maximum brightness, not by software but as i tap more the brightness does not increase. After pressing the brighter key for the first time it takes about 2 seconds till the backlight turns off, after i dim the screen on the software and but it back on it works for 2 seconds again. So I have to click f1 and f2 every 2 seconds to be able read. Hence, I think there is something wrong with the dimmer and brightener. I'm not sure how apple has done it but as it should be normal resistance trick i don't think that the problem is so much on the resistance but on the mechanism that controls the amount of resistance. That still does not explain why the light does not stay on. The angle of my screen respective to the keyboard does not effect. Any ideas?