Going beyond the 20th century color space to evaluate LED color consistency

Abstract

The color matching possibilities between (reference) phosphor-converted LEDs (pc-LEDs) and replacement metameric LEDs made by color mixing technology (cm-LEDs) were evaluated in the classical 20th century CIE 1976 color space developed for perpendicular viewing (based on a 2° colorimetric observer) and in the latest CIE 2015 cone fundamental color space developed for wide field of view observers (10° colorimetric observer). For each given pc-LED 10 different sets of cm-LEDs were designed and evaluated for color consistency in 2°and 10° color spaces. There were 10 different B-color LEDs considered along with constant RGA LEDs. There are thousands of possible distributions that are metameric in the CIE 1976 color space and thousands of possible distributions that are metameric in the CIE 2015 color space for each set of LEDs. From the population of SPDs, we selected 10 metameric SPDs characterized by maximum differences between chromaticities. The results provide evidence that evaluating LED color consistency based only on the CIE 1976 color space is not fully informative because it may provide inaccurate information about light color consistency when the observer has a wide field of view. There are cases showed in this paper where cm-LEDs are color consistent in the CIE 2015 color space but are not color consistent in the CIE 1976 color space and vice versa. Including color consistency in the new CIE 2015 color space should be treated as an additional evaluation tool proving the user additional information relevant to the intended use of the LED. The results illustrate differences in LED color consistency evaluated in different color spaces and provides incentive go beyond the 20th century color space in the evaluation of cm-LED color consistency.