BootCamp Brightness in Windows 7 and 8

If it seems like you just can’t get the screen bright enough, try this:

The problem is due to Adaptive Brightness.

This is what you need to do if the screen does not go past a certain brightness level on Windows 7 or Windows 8.

1. Go to the Start bar on the Desktop and move your mouse all the way to the right to find the Battery icon.
2. Click the battery icon. A little popup box should show up. Click “More Power Options”
3. Select your plan and click “Change Plan Settings”
4. Click “Change Advanced Power Settings”
5. Scroll down to Display and click the little + sign next to it.
6. Scroll down to “Enable Adaptive Brightness” and click the little + sign next to it.
7. Change “On Battery” and “Plugged In” to make sure it is Off for both of them.

source: https://discussions.apple.com/thread/2669574?start=120&tstart=0