MacBooks come with a light sensor that automatically adjusts the screen's brightness based on ambient lighting, but you can override the sensor's behavior. If you are in a bright room, increasing the contrast can make the screen easier to read. If you're in a dark room, try inverting the screen's colors. This capability is a great feature when you're reading an e-book, for example. Instead of white pages with black text, inverted colors give you black pages with white text.
Press the F1 key, which has a small light icon on it, to reduce brightness. To increase brightness, press the F2 key, which has a larger light icon. As you reduce or increase brightness the light icon appears on the screen. The bars below the icon indicate how dim or bright the screen is.
Click the Apple menu and select System Preferences. Click the Display icon.
Click the Automatically Adjust Brightness check box to enable or disable the MacBook's light sensor. To manually control the brightness, drag the slider as desired. The slider works whether the light sensor is enabled or disabled.
Adjusting Contrast and Inverting the Display
Select System Preferences from the Apple menu. Click the Accessibility icon.
Click the Increase Contrast button to make the distinction between light and dark colors more noticeable.
Click the Invert Colors button. Instead of a white screen with dark letters, the screen turns black with white letters. If the strange color schemes are too difficult to look at, click the Use Grayscale option as well.