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Glossary of Terms

Glossary of Terms


The CIE (Commission Internationale de l’Eclairage) is the international standards organization responsible for setting standards for color and color measurement.

CIE 1976 U.C.S Chromaticity Diagram.
U.C.S stands for Uniform Color Space, Uniform Color Scale, Uniform Chromaticity Scale, or Uniform Chromaticity Space. The chromaticity diagram is a tool to specify how the human eye will experience light with a given spectrum.

The CIE U.C.S is another name for the (u, v) chromaticity space devised by David McAdam.

In 1976 the CIE recommended the adoption of two new color spaces (CIELUV and CIELAB). CIELUV is only a minor modification of the CIE 1964 color space, and includes a new u’v’ chromaticity diagram which replaces the 1960 UV diagram. Correlated color temperature can be calculated using the new diagram, leading to somewhat different results.

CIE Tristimulus Value

Indicates the amounts of the three primaries (XYZ) required to match a color sample.

CIE XYZ Color Space

XYZ is the first of a series of mathematical models that describe color in terms of synthetic primaries based on human perception. They are imaginary mathematical constructs that model the human eyes’ response to different wavelengths of light.


A mathematical derivative of CIE XYZ that describes colors using three synthetic primaries: L (Lightness), a* (red-greenness), and b* (yellow-blueness).

Cold Cathode Fluorescent Lamp (CCFL)

Cold Cathode lamps use a cylindrical metal shell (electrode) coated on the inside with emission coating.  A cold cathode is distinguished from a hot cathode in that unlike hot cathode lamps that are heated to induce thermionic emission of electrons, cold cathode lamps are not.  The interior surface of cold cathodes are capable of producing secondary electrons upon electron and ion impact. For acceleration of the ions to reach a sufficient velocity for creating free electrons from the cathode material, cold cathode discharge lamps need higher voltages (and therefore lower current) than hot cathode lamps.


Color Rendering Index

Hot Cathode Fluorescent Lamp (HCFL)

Hot cathode lamps use a tungsten filament typically covered with an emissive layer, made of a material with lower work function, which emits electrons more easily than bare tungsten metal, reducing the necessary temperature and lowering the emission of metal ions and heated to orange-hot.  The filament may be either directly heated, where the filament itself is the source of electrons, or indirectly heated, where the filament is electrically insulated from the cathode.  Hot cathodes typically achieve much higher power density than cold cathodes, emitting significantly more electrons from the same surface area resulting in higher output and can operate at higher lamp currents.

LCD – Liquid Crystal Display

A liquid crystal display (LCD) is a thin, flat electronic visual display that uses the light modulating properties of liquid crystals (LCs). They are considered a passive display because they need a light source to illuminate the LCs.  LCDs can be designed for both special and general uses, including computer monitors, television, instrument panels, aircraft cockpit displays, signage, and more. They are also common in many consumer devices such as video players, gaming devices, clocks, watches, calculators, and telephones.

Lightness (sometimes called tone)

Reflects the subjective brightness perception of a color for humans along a lightness–darkness axis.

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