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Applied Optics

Applied Optics


  • Vol. 38, Iss. 27 — Sep. 20, 1999
  • pp: 5703–5709

Calculating correlated color temperatures across the entire gamut of daylight and skylight chromaticities

Javier Hernández-Andrés, Raymond L. Lee, Jr., and Javier Romero  »View Author Affiliations

Applied Optics, Vol. 38, Issue 27, pp. 5703-5709 (1999)

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Natural outdoor illumination daily undergoes large changes in its correlated color temperature (CCT), yet existing equations for calculating CCT from chromaticity coordinates span only part of this range. To improve both the gamut and accuracy of these CCT calculations, we use chromaticities calculated from our measurements of nearly 7000 daylight and skylight spectra to test an equation that accurately maps CIE 1931 chromaticities x and y into CCT. We extend the work of McCamy [Color Res. Appl. 12, 285–287(1992)] by using a chromaticity epicenter for CCT and the inverse slope of the line that connects it to x and y. With two epicenters for different CCT ranges, our simple equation is accurate across wide chromaticity and CCT ranges (3000–106 K) spanned by daylight and skylight.

© 1999 Optical Society of America

OCIS Codes
(010.1290) Atmospheric and oceanic optics : Atmospheric optics
(330.1710) Vision, color, and visual optics : Color, measurement
(330.1730) Vision, color, and visual optics : Colorimetry

Original Manuscript: March 1, 1999
Revised Manuscript: June 8, 1999
Published: September 20, 1999

Javier Hernández-Andrés, Raymond L. Lee, and Javier Romero, "Calculating correlated color temperatures across the entire gamut of daylight and skylight chromaticities," Appl. Opt. 38, 5703-5709 (1999)

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