In colorimetry and color theory, lightness, also known as value or tone, is a representation of variation in the perception of a color or color space's brightness. It is one of the color appearance parameters of any color appearance model.
Various color models have an explicit term for this property. The Munsell and HSV color models use the term value, while the HSL color model, HCL color space and Lab color space use the term lightness.
In some of these models (Munsell, HCL and Lab), the lightness or value is the absolute brightness. In Munsell, for example, the only color with value 0 is pure black, and the only color with value 10 is pure white. Colors with a discernable hue must have values in between these extremes.
In HSL and HSV, the lightness or value is a relative brightness. Both systems use coordinate triples, where many triples can map onto the same color. In HSV, all triples with value 0 are pure black. If the hue and saturation are held constant, then increasing the value increases the brightness, such that a value of 1 is the brightest color with the given hue and saturation. HSL is similar, except that all triples with lightness 1 are pure white. In both models, all pure saturated colors have the same lightness or value, and the absolute brightness is determined by the hue: yellow is brighter than blue.
In subtractive color (e.g., paints) value changes through various tints and shades can be achieved by adding black or white, respectively, to the color. However, this also reduces saturation. Chiaroscuro and Tenebrism both take advantage of dramatic contrasts of value to heighten drama in art. Artists may also employ shading, subtle manipulation of value.