Color Quality Scale

The color quality scale (English Color quality scale, CQS ) means a quantitative method for determining the color rendering of a light source. A spectrally measured light source obtained with the method is a numerical value between 0 and 100, the index of a light source describes the rendering property for color to a comparable reference light source. CQS was developed by NIST to replace some shortcomings and having common color rendering index Ra. Similar to many other rating scales of the colorimetry color quality scale assesses playing single standardized color samples.

History

The standardized color rendering index contains a very simple metric, it compares the test with reference light source using eight unsaturated color cards. The aim of its introduction was to evaluate the color fidelity of fluorescent lamps. This objective was well met with this standard. In the evaluation of other light sources, however, he showed weaknesses.

There have been several proposals to replace the color rendering index, this could not displace the established standard. None of the proposals itself was standardized. Proposed replacement standards were:

  • " 8 -band Spectral Band Method " derived from full radiator
  • Flattery Index for Artificial Illumination ( Deane Judd, 1967)
  • Color Discrimination Index ( Thornton, 1972)
  • Color Preference Index ( Thornton, 1974)
  • Cone Surface Area ( Fotios, 1997)
  • Color Rendering Capacity ( Xu, 1993)
  • Feeling of Contrast Index ( Hashimoto, Yano, Nayatani, 2000)

With the increasing amount of LED light sources changes of colorimetry were necessary because of the color rendering index of disadvantage certain LED light sources over other light sources. Studies on the subjective color appearance showed the poor correlation between perceived color quality and color rendering index.

Differences to the color rendering index

The test colors on the color quality scale, in contrast to Ra all saturated. Only in this way can be a valid statement about the reproduction of saturated colors. In the color quality scale acceptance is highlighted that the unsaturated colors are just as well represented by the light source due to economies of scale. The newer approach succeeds again by comparison with a reference light source, this is not considered as the measure of all things, however, an over-emphasis of one color will not be negatively rated, alsoim CQS not be punished. In the color quality scale is the numerical value as the geometric mean - determined - not like the color rendering index as the arithmetic mean. This leads to a stronger devaluation of individual particularly poorly reproduced colors.

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