Lichtheit

Lichtheit is a perceptual attribute of color describing the degree to which a color appears light or dark. It is primarily a perceptual construct, intended to reflect how the human eye perceives lightness independent of hue and saturation. In color science, it is closely related to the concept of lightness used in color appearance models such as CIELAB and CIECAM02.

In these models, Lichtheit is represented by a value often denoted L*, which ranges roughly from 0 (black) to 100 (white). L* is derived from the measured tristimulus coordinates and is transformed through a nonlinear function designed to approximate human perception. It is important to note that L* is not identical to physical luminance (Helligkeit), which is a photometric measure of radiant power per unit area. Luminance depends on the observer's adaptation, illumination, and geometry, whereas Lichtheit strives for perceptual uniformity.

Applications include digital imaging, color management, printing, and design, where perceptual brightness adjustments are preferable to simple linear changes in pixel values. In practice, Lichtheit can be influenced by surrounding colors, context, and adaptation state, which can affect perceived brightness even if the physical stimulus remains constant.

Limitations include context dependence and variability across observers and lighting conditions. Nevertheless, Lichtheit remains a central concept in modern color science for describing how bright a color appears to human observers.

See also: lightness, luminance, Helligkeit, CIELAB, color appearance models.