Color Quality Scale

Color Quality Scale

Color Quality Scale Measuring the color quality of light sources Marcel van der Steen, www.OliNo.org Materials used Toward an improved color rendering metric, W. Davis and

Y. Ohno, 2005 Presentation CQS Wendy Davis 2010 Rationale of color quality scale, W. Davis and Y. Ohno, 2010 Color Quality Scale Excel file v 9.0.3 Y. Ohno+notes 2011 Presentation Color Perception and Lighting by Sophia Sotiropoulou 2013

Marcel van der Steen, www.OliNo.org Color Rendering Marcel van der Steen, www.OliNo.org Good color rendering costs lm/W

Marcel van der Steen, www.OliNo.org Color rendering index (CRI) Marcel van der Steen, www.OliNo.org Measuring color differences

Marcel van der Steen, www.OliNo.org Color spaces for meas. difference 15 reflective CQS samples in CIE 1976 L*a*b* and CIE 1964 W*U*V* color spaces CIE 1964: color differences extremely exaggerated in red and suppressed in yellow and blue regions. Marcel van der Steen, www.OliNo.org

Color rendering index (CRI) The CRI was designed to evaluate fluorescent lamps The CRI was intended to measure the naturalness of objects colors, not preference Reflective samples (1st eight) chosen to represent average saturation of objects, not fully saturated

Has had no substantive changes in 35 years Narrowband LED spectra showed the characterizing limits of CRI LEDs CRI result does not correspond to its: 1) level of being visually appealing, 2) naturalness, 3) ability to discriminate between colors Marcel van der Steen, www.OliNo.org

Problems with the CRI Marcel van der Steen, www.OliNo.org Saturation and Naturalness Marcel van der Steen, www.OliNo.org

Problems with the CRI Marcel van der Steen, www.OliNo.org Problems with the CRI Marcel van der Steen, www.OliNo.org

Color quality scale (CQS) Marcel van der Steen, www.OliNo.org Color quality scale (CQS) Marcel van der Steen, www.OliNo.org

Reflective sample set Marcel van der Steen, www.OliNo.org Root mean square Marcel van der Steen, www.OliNo.org

Saturation factor A: not penalized for increase of chroma (however there is a limit since v9, see next page) B: penalized for decrease of chroma C: penalized for hue shift, but not for increase of chroma (however a limit, see next page) Marcel van der Steen, www.OliNo.org

Saturation factor since v9.0 Max tolerable increase in chroma is +10 Marcel van der Steen, www.OliNo.org Saturation factor example

Color-desaturating light (Ra=82, Qa=74) Color-enhancing light (Ra=71, Qa=83) Marcel van der Steen, www.OliNo.org New scaling factor The CQS prevents

negative values. CRI values below 35 are affected. Values below 35 indicate bad rendering. Marcel van der Steen, www.OliNo.org

Chromatic adaptation (correction) Chromatic adaptation is the ability of the human visual system to discount the color of the illumination and to approximately preserve the appearance of an object (e.g. white sheet of paper under different illuminants) CQS uses a newer Chromatic Adaptation

Transform (CMCCAT2000) than CRI does. Marcel van der Steen, www.OliNo.org Chromatic adaptation Marcel van der Steen, www.OliNo.org

CCT factor and removal Light with low CCT (say < 2500K) and even CRI=100, cannot render well blue tones. One cannot distinguish black and blue socks with halogen light as there is little blue in it

To correct for this, the max CQS value should be less than 100 for low CCTs. A proposal was in v7.5 but removed in v9.0 due to some opposition of industry people and the lack of experimental validation. This factor could come back later.

CCT [K] Mult.Fctr. 1000 0.19

1500 0.64 2000 0.87

2500 0.96 2856 0.98

3000 0.99 3500 and up 1.00 Marcel van der Steen, www.OliNo.org

Evaluation room at NIST Marcel van der Steen, www.OliNo.org Experimental spectra Marcel van der Steen, www.OliNo.org

Results: Room evaluation Marcel van der Steen, www.OliNo.org Results: Skin evaluation Marcel van der Steen, www.OliNo.org

CQS available The CQS v9.0 will from mid Feb be an addition to OliNo lamp measurements Some changes may occur as the metric is not adopted yet (scaling factor)? The metric has many improved elements over the CRI More Info: www.OliNo.org

Marcel van der Steen, www.OliNo.org

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