Though all modern Apple laptops have brightness controls for dimming the screen in dark conditions, there are several situations where the built in controls are unsatisfactory. The granularity of control is rather coarse, and the minimum brightness setting still quite bright when working in pitch darkness.

Perhaps you need to use your machine in a darkroom, or like to work late at night without disturbing your partner who sleeps beside you?

Perhaps you need to dim the screen on a desktop machine, and the display you are using offers no such facility?

If this is the case for you, then try Shades.

Note: Shades may interfere with colour calibration software, and should not be used if colour accuracy is critical.