I’ve had this problem for a while but I recently found a solution. If you’ve installed Windows 7 on your Mac through Bootcamp, you’ll realize that you can’t change the screen’s brightness. This is because PCs and monitors and separate units, and the monitors have physical brightness control buttons. On a Mac (being the beautiful machine it is), you won’t find these physical brightness (and contrast) buttons.
The first thing you should check is your control panel. In the Start menu, search for Power Options and open the Power Options settings:
Click on “Change plan settings,” and the majority of people will find brightness options.
In case this method doesn’t work for you, the following back-end method definitely will.
In your Start menu, search for “Color Management”:
Click on the “Advanced” tab:
Then click on “Calibrate Display.”
An almost full-screen window will open with a gray background. Follow the instructions and keep clicking the “Next” button until you see RGB sliders like these:
Drag each slider to the left. During the process, your monitor will be tinted different colors (blue, red, etc.), but ignore this effect.
Once you have dragged each slider fully to the left, you should have a darker, non-tinted screen.
Continue clicking the “Next” button until you complete the calibration process (ignore ClearType tuner).
I hope this method worked for you because it worked for me. If you have additional questions, post a comment! It might help someone else as well.