Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. ... Brightness refers to how much light appears to shine from something. This is a different perception than lightness, which is how light something appears compared to a similarly lit white object.

How does phone brightness work?

In a smartphone the light sensor is facing your head and is measuring the brightness of your face instead of the ambient light level that is behind and to either side of the phone, which is what actually sets your eye's light sensitivity and what should be determining the brightness level of the screen.

What does the brightness do?

– Brightness refers to the absolute value of colors (tones) lightness/darkness. Increasing brightness of an image will light out all colors so the original light ones will become up to white. Reversely, decreasing brightness will darken all colors so the original shaded ones will become up to black.