Brightness is a measure of the light output emitted by a screen. If the light output is high, the viewer perceives the image as bright, if it is low, he perceives it as dark. The brightness is evaluated using the unit of measurement candela/sqm.
A brightness that is perceived as pleasant has about 200 candela/sqm. In addition to hue
and color contrast, brightness is decisive for the recognition of image details. Depending on the color range, the human eye can distinguish between 16 and 26 different brightness values, whereby the perception of brightness is logarithmic. Darker brightness values therefore require only a fraction of the actual intensity. For example, a 50% grey value can be produced with only about 20% of the intensity that would be needed for the white value, i.e. the 100% value. The efficiency of light conversion, or efficacy, is 680 lumens per watt (lm/W) for daylight, at a light wavelength of 555 nm.