luminosity, also called clarity, is a property of colors. It gives an indication of the luminous aspect of the color studied: the darker the color, the weaker the luminosity. This term is sometimes associated with the concept of value, luminance, light.

The definition used in photometry and colorimetry describes the non-linear perception we have of the amount of light received. It is often defined from the luminance of the source studied.

Luminosity is used in colorimetry to define certain colorimetric systems called uniform chromatic systems such as CIE LUV), CIE L*a*b*, and others.

A color can be rated according to its luminosity. In the following example you can see the following adjectivizations:[1]​.

Contenido

La CIE definió la luminosidad, L*, también llamada claridad, en este caso, a partir de la luminancia Y del color, expresada en candelas por metro cuadrado (cd.m), en relación con la luminancia del [color] blanco tomado como referencia. La luminosidad toma en este caso un valor entre 0 y 100:[2]​.

Escrito de una manera más legible se tiene:.

Explanation

The function is defined differently on two intervals to avoid an infinite derivative for . The function is linear below the value : . To ensure that yes, it is necessary that. Next, the continuity of the function and its derivative are assured for this value:.

This is how you have it:

In the case of primary sources, the reference white is the brightest white (generally the D65 illuminant) that the source (television, projector,...) can produce. In the case of secondary sources, they are compared with magnesium oxide (MgO) which has a reflectance factor of 97.5%.

A gray with a reflectance of 18% (photometrically as well as energetically or radiometrically) will have a lightness of around 50%.