What Does Brightness Mean?
Brightness is the perceived intensity of light coming from a screen. On a color screen, it is the average of the red, green and blue pixels on the screen. Brightness is important to both color perception and battery life on mobile devices. It can be adjusted manually or automatically with sensors.
Techopedia Explains Brightness
Brightness is the perception of how intense the light coming from a screen is. Although it is subjective, in can be measured in terms of the amplitude of the light being emitted from a screen.
Color screens use three colors under the RGB scheme: red, green and blue. The brightness of a screen can be represented by the sum of the amplitude of red, green and blue pixels divided by three. In other words, the average of the three colors.
Perception of brightness can be altered by certain optical illusions to appear brighter or darker. As brightness decreases, colors appear washed out, but "purer" as brightness increases.
On mobile devices, higher brightness settings can cause the device's battery to drain faster compared to a lower setting. Many mobile devices have an ambient light sensor to automatically adjust brightness to a comfortable level based on the light in a room.