Ambient light sensor

An ambient light sensor measures light around a device. Automatic brightness can use this information to adapt a display to a bright room or dim surroundings. The sensor measures the environment, rather than the light emitted by the panel.

A lux reading and a display's brightness in nits therefore describe different things. A sensor can also supply information used by True Tone, which adapts the display's color appearance.

In BetterDisplay, group synchronization can follow brightness changes made by a display's automatic brightness system. That does not imply that BetterDisplay directly reads every sensor or that all monitors have one. See Synchronization Settings and Apple's True Tone explanation.