Where are we going to? Yoshi Ohno (Ph.D., CIE President, IES - - PowerPoint PPT Presentation

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Where are we going to? Yoshi Ohno (Ph.D., CIE President, IES - - PowerPoint PPT Presentation

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EPA Energy Star Lighting Webinar Series Evaluating Color Quality March 31, 2016 Color Quality of Lighting and Metrics Where are we going to? Yoshi Ohno (Ph.D., CIE President, IES Fellow) NIST Fellow, Sensor Science Division National

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Energy Star Webinar March 2016

Color Quality of Lighting and Metrics – Where are we going to?

Yoshi Ohno

(Ph.D., CIE President, IES Fellow)

NIST Fellow, Sensor Science Division National Institute of Standards and Technology Gaithersburg, Maryland USA

EPA Energy Star Lighting Webinar Series Evaluating Color Quality – March 31, 2016

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Color Quality of Lighting

Chromaticity

(white light)

Color Rendition Color Quality

400 450 500 550 600 650 700 400 500 600 700
  • CCT, Duv
  • Chromaticity

coordinates (x,y), (u’,v’)

  • Color fidelity (CRI)
  • Color preference
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Energy Star Webinar March 2016

OUTLINE

  • 1. Research on White Light Chromaticity
  • 2. Research on Color Saturation Preference
  • 3. Understanding TM-30
  • 4. Where are we going to?
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OUTLINE

  • 1. Research on White Light Chromaticity
  • 2. Research on Color Saturation Preference
  • 3. Understanding TM-30
  • 4. Where are we going to?
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Color Quality = CCT and CRI ?

CCT: Correlated Color Temperature (CIE S017 ILV) CRI: Color Rendering Index (CIE 13.3)

Some example CCT = 3050 K CRI (Ra)= 91 This product is not acceptable. Why? Too yellowish!

Normal

CCT does not tell the whole story of chromaticity. Duv

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White Light Chromaticity

ANSI C78.377 for SSL

  • Widely used, in Energy Star, DLC,

IEA SSL Annex ,etc.

  • First published in 2008
  • Revisions in 2011, 2015

ANSI C78.376-2001 for linear fluorescent lamps

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Annex B. 4-step quadrangle tolerances

ANSI C78.377 Future Considerations

Annex C. 4-step u’v’ circles

(CIE TN001)

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An example: Neodymium lamp

Preference to below blackbody

Known for many years but not covered in any standards.

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Recent Studies

Experiment on perceived white point by LRC (2013) Experiment on preferred lighting by NRC, Canada (2013)

NIST vision experiment in 2013

Dikel et al, ”Preferred Chromaticity of Color- Tunable LED Lighting”, LEUKOS, 10:2, 101- 115, DOI: 10.1080/15502724.2013.855614 (2013).

Ohno, Y., Fein, M., Vision Experiment on Acceptable and Preferred White Light Chromaticity for Lighting, CIE x039:2014,

  • pp. 192-199 (2014).
  • M. S. Rea,* J. P. Freyssinier, “White

Lighting”, CR&A, 30-2, 82-92, 2013.

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NIST Spectrally Tunable Lighting Facility

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NIST Spectrally Tunable Lighting Facility

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6 Duv points at each CCT, 4 CCTs, at total 23 points. Total 50 spectra used.

  • NIST STLF at ~ 300 lx.
  • 18 subjects (20 to 70 yrs old)
  • Viewed fruits/vegetables on the table,

his/her skin tone and the whole room.

  • Adapted to each Duv point before

judgement: which light is “more natural”.

2013 Vision Experiment at NIST

  • n Preferred and Acceptable level of Duv

Adaptation points

Pair

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Which light looks more natural? A

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Which light looks more natural? A Which light looks more natural? B

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  • NIST STLF at ~ 300 lx.
  • 18 subjects (20 to 70 yrs old)
  • Viewed fruits/vegetables on the table,

his/her skin tone and the whole room.

  • Adapted to each Duv point before

judgement: which light is “more natural”.

2013 Vision Experiment at NIST

  • n Preferred and Acceptable level of Duv

Duv=~ -0.015 at all CCTs appeared most natural. Average results of all subjects

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  • NIST STLF at ~ 300 lx.
  • 18 subjects (20 to 70 yrs old)
  • Viewed fruits/vegetables on the table,

his/her skin tone and the whole room.

  • Adapted to each Duv point before

judgement: which light is “more natural”.

2013 Vision Experiment at NIST

  • n Preferred and Acceptable level of Duv

Further reference

Y, Ohno, “Practical Use and Calculation of CCT and Duv” LEUKOS 10:1, 47-55, DOI: 10.1080/15502724.2014.839020 (2013).

Duv defined in ANSI C78.377.

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Discussion by Minchen Wei & Kevin Houser

LEUKOS, DOI:10.1080/15502724.2015.1029131, April 2015

  • Vol. 12, Issue 1-2, 2016

“We infer that the preference expressed by participants in the studies by Dikel and others [2014] and Ohno and Fein [2014] may not be solely related to chromaticity.” “aspects of color rendition (that is, color fidelity and relative gamut) may also influence preference.”

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Chroma saturation

2013 Experiment 2015 Experiment

Chroma saturation (red, green)

3500 K 3500 K

Gamut area Qg Gamut area Qg

3500 K 3500 K

Chroma saturation (red, green)

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Chroma saturation

2013 Experiment 2015 Experiment

Chroma saturation (red, green)

3500 K 3500 K

Gamut area Qg Gamut area Qg

3500 K 3500 K

Chroma saturation (red, green)

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Average Results of 2015 vs 2013 Experiment

2013 results 2015 results No significant differences found.

Std.dev Ohno, Y., Fein, M., Vision Experiment on Acceptable and Preferred White Light Chromaticity for Lighting, CIE x039:2014, pp. 192-199 (2014) Ohno, Y., Oh, S., Vision Experiment II on White Light Chromaticity for Lighting, CIE x042:2016, pp. 175-184 (2016)

References

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Current specification

Proposal for addition to ANSI C78.377

Flexible Duv

(Center Duv

  • 0.002 to -0.012)

“Preference-based” (Center Duv -0.012 )

Proposal

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OUTLINE

  • 1. Research on White Light Chromaticity
  • 2. Research on Color Saturation Preference
  • 3. Understanding TM-30 and CRI
  • 4. Where are we going to?
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Why perception differ from the CRI scores?

Plots of 15 CQS samples

  • n CIELAB

(a*,b*) Red and green are critical Test light (Ra=78) Reference (Planckian)

The area within such plots is called “gamut area”

CRI Ra=78 CRI Ra=94

  • CRI is a color fidelity metric based on Reference Illuminant.
  • Perception is different from color fidelity

Looks better (for most people)

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Ra=82 Ra=82

Color Gamut and Perception

De-saturated Neutral Over-saturated

Looks poor Good Looks better

(to some extent)

Ra=63 Ra=100 Ra=85

Perception and CRI agree (CRI works okay) Perception and CRI do not agree

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Most saturated Most de-saturated

  • 80
  • 60
  • 40
  • 20

20 40 60 80 100

  • 80
  • 60
  • 40
  • 20

20 40 60 80

a*

CIELAB

b*

DC*

ab = -16

DC*

ab = 16

2014 Vision Experiment at NIST

  • n preferred chroma saturation level
  • 20 subjects
  • 3 CCTs (2700, 3500, 5000 K), Duv= 0
  • 3500 K, Duv= -0.015
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Which light looks better? A

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Which light looks better? A Which light looks better? B

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Results

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

  • 16
  • 12
  • 8
  • 4

4 8 12 16 Percent of Participants who preferred the Point Average Preference for DC Average Room Skin Green Red

 More saturated De-saturated  Neutral

  • Y. Ohno, M. Fein, C. Miller, Vision Experiment on Chroma Saturation

for Color Quality Preference, CIE 216 :2015, pp. 60 – 69 (2015)

DCab

*

CRI Ra

100 90 80 70 60

(1) Entire room (2) Skin tone of subject (3) Red fruits/vegetables (4) Green fruits/vegetables

Reference:

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OUTLINE

  • 1. Research on White Light Chromaticity
  • 2. Research on Color Saturation Preference
  • 3. Understanding TM-30
  • 4. Where are we going to?
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 Two-metric system

  • Fidelity index Rf
  • Gamut index Rg

 99 test samples  Latest color space and chromatic adaptation formula  Calculation tool

IES TM-30 IES Method for Evaluating Light Source Color Rendition

Color fidelity: Improvement

  • f CRI Ra

Information for preference

Works accurately for all colors of

  • bject and all

spectra

Provide details beyond Rf and Rg.

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Image from Michael Royer

Concept of Two-Metric System

Gamut Rg Fidelity Rf Preferred?

  • Rg provides preference-related

information.

  • TM-30 does not provide

design guidance for Rg

  • Limitation of Rg - ave. of all hues

Rg=100 Rf=75 Rg=100 Rf=75

Rg equal but different shapes More saturated Less saturated

Gamut area is not sufficient.

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IES Position statement of CRI – 2015

  • IES recognize that CIE CRI has

shortcomings, especially with new lighting technologies. TM-30 was developed to solve this problem.

  • “TM-30-15 is not a required standard,

and it does not provide design guidance or criteria for best practices.”

  • “the issuance of TM-30-15 will enable

the international lighting community to carefully evaluate it, providing a path leading to improved standards and design guidance.”

Issued Sep. 2015

Link: https://www.ies.org/PDF/PositionStatements/PS-8-15.pdf

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CIE Position statement on CRI and Color Quality Metrics

Issued Oct. 2015.

  • CRI has several significant sources of colorimetric
  • inaccuracy. CRI needs to be updated. CIE TC1-90

is developing a new color fidelity metric.

  • CIE supports the study of the recently published

IES TM-30. TC1-90 accepted TM-30 Rf metric as basis for the TC’s first draft.

  • An orderly transition is needed when a new

metric is to be introduced.

  • Both TC reports to be completed by end of 2016.
  • The colour fidelity metrics including the CRI do

not assess other important aspects of the colour qualities of light sources, in particular, those related to colour preference. CIE TC 1-91 is developing a Technical Report on this subject.

Link: http://www.cie.co.at/index.php ?i_ca_id=981

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GLA (Global Lighting Association) Position statement on CRI

  • GLA cautions against the establishment
  • f regulatory or other minimum

performance requirements for a colour rendering index (Ra) of greater than 80 for indoor lighting applications.

  • GLA supports the need for an additional

colour quality metric - for example, a colour saturation metric, in conjunction with the well-established fidelity metric Ra.

Link: http://www.globallightingassociation.org/library (2nd item on this page)

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Color Rendition Color Fidelity Color Preference CRI Ra (CIE 13.3) TM-30 Rf

New int’l recommendation

  • n Color Fidelity Index

CIE TC1-91

Int’l recommendation on color-preference metric(s)

Where are we going to?

CIE TC1-90

Many other inputs

New TC

TM-30 Rg

  • Gradual transition from CRI.
  • Two (or more) numbers will be

used to specify color quality.

Current int’l std. More research No standards (CIE’s perspective)

  • Tech. report (no

recommendation)

2017

Chromaticity ANSI C78.377

Addition of preference- based specification Smaller tolerances

?

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THANK YOU for your attention.

Contact: Yoshi Ohno

  • hno@nist.gov

We thank DOE for their support on NIST research on SSL metrology and color quality.