Lightness

Lightness is a visual perception of the luminance of an object. It is often judged relative to a similarly lit object. In colorimetry and color appearance models, lightness is a prediction of how an illuminated color will appear to a standard observer. While luminance is a linear measurement of light, lightness is a linear prediction of the human perception of that light. This distinction is meaningful because human vision's lightness perception is non-linear relative to light. Doubling the quantity of light does not result in a doubling in perceived lightness, only a modest increase. The symbol for perceptual lightness is usually either as used in CIECAM02 or as used in CIELAB and CIELUV. ("Lstar") is not to be confused with as used for luminance. In some color ordering systems such as Munsell, Lightness is referenced as value. 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. In some colorspaces or color systems such as Munsell, HCL, and CIELAB, the lightness (value) achromatically constrains the maximum and minimum limits, and operates independently of the hue and chroma. For example Munsell value 0 is pure black, and value 10 is pure white. Colors with a discernible hue must therefore have values in between these extremes. In a subtractive color model (e.g. paint, dye, or ink) lightness changes to a color through various tints, shades, or tones can be achieved by adding white, black, or grey respectively. This also reduces saturation. In HSL and HSV, the displayed luminance is relative to the hue and chroma for a given lightness value, in other words the selected lightness value does not predict the actual displayed luminance nor the perception thereof. 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 luminance, such that a value of 1 is the lightest color with the given hue and saturation.