Another important characteristic of a white light source is its ability to show (i. e. render) the true colors of physical objects, e. g. fruits, plants, or toys, that are being illuminated by the source. The ability to render the colors of an object is measured in terms of the color-rendering index or CRI (Wyszecki […]

19.1 Additive color mixing The combination or additive mixing of two or more light sources is employed in a number of applications. In LED displays, three different types of LEDs, usually emitting in the red, green, and blue, are used. The three colors are mixed so that the observer can experience a wide range of […]

Color temperature may appear to be a somewhat surprising quantity as color and temperature don’t seem to have a direct relationship with each other. However, the relationship is derived from Planck’s black-body radiator. With increasing temperatures, it glows in the red, orange, yellowish white, white, and ultimately bluish white. The color temperature (CT) of a […]

White light usually has a broad spectrum extending over the entire visible range. An instructive model for white light is sunlight. The sun’s optical spectrum is shown in Fig. 18.1, including the spectrum at sea level with the sun at zenith, incident above the earth’s atmosphere, and at sunset and sunrise (Jackson, 1975). The spectrum […]

Having completed the discussion of chromaticity allows us to revisit the question: What is color? One could certainly define a color by its location in the chromaticity diagram (i. e. by its chromaticity). However, the CIE (1986) adopted a more general definition of the term “color” that goes beyond the location in the chromaticity diagram. […]

Monochromatic light sources (AX ^ 0) are located on the perimeter of the chromaticity diagram. Light emission from LEDs is monochromatic (single color) to the eye but LEDs are not monochromatic in the strict physical sense since LEDs have a spectral linewidth of about 1.8 kT. Owing to the finite spectral linewidth of LEDs, they […]

Monochromatic sources (AX ^ 0) are located on the perimeter of the chromaticity diagram. However, as the spectral linewidth of a light source gets broader, the color location in the chromaticity diagram moves towards the center of the chromaticity diagram. If the spectral width of a light source becomes comparable to the entire visible range, […]

Light causes different levels of excitation of the red, green, and blue cones. However, the sensation of color and luminous flux caused a particular light source varies slightly among different individuals. Furthermore, the sensation of color is, to some extent, a subjective quantity. For these reasons, The International Commission for Illumination (Commission Internationale de I’Eclairage, […]

The assessment and quantification of color is referred to as colorimetry or the “science of color”. Colorimetry is closely associated with human color vision. Both colorimetry and human vision have attracted a great deal of interest that spans many centuries. For a thorough and entertaining review of the history of colorimetry including early attempts to […]

The human wake-sleep rhythm has a period of approximately 24 hours and the rhythm therefore is referred to as the circadian rhythm or circadian cycle, with the name being derived from the Latin words circa and dies (and its declination diem), meaning approximately and day, respectively. Light has been known for a long time to […]