1

Spectral Power Distributions and their use in applied lighting

Michael Royer, PhDPacific Northwest National Laboratory

1. Basics of light and vision

2. Spectral data

• Types of SPDs

• Relative vs. Absolute SPDs

• Data formats

3. SPD-based calculations

• Lumens

• CCT/Duv/Chromaticity

• Melanopic Flux/CS

4. Color rendition

3

4

5

6

7

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

380 430 480 530 580 630 680 730 780

Rela

tive

Sens

itivi

ty

Wavelength (nm)

Erythropic Slc(λ)Chloropic Smc(λ)Cyanopic Ssc(λ)Melanopic Sz(λ)Rhodopic Sr(λ)

(Long Cone)

(Medium Cone)(Short Cone)

(ipRGC)

(Rod)

UnivarianceNo single photoreceptor can detect wavelengths.

8

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

380 430 480 530 580 630 680 730 780

Rela

tive

Sens

itivi

ty

Wavelength (nm)

Erythropic Slc(λ)Chloropic Smc(λ)Cyanopic Ssc(λ)Melanopic Sz(λ)Rhodopic Sr(λ)

(Long Cone)

(Medium Cone)(Short Cone)

(ipRGC)

(Rod)

S M L

Blue-YellowL-S

Red-GreenL-M

Black-WhiteL+M

[achromatic][chromatic]

Photoreceptor Stage

Neural Stage

Rods(?)ipRGCs(?)

2. Light Source SPDs

10Note: Light sources technologies are not homogenous!

Chromatic AdaptationIndependent control of

color signals in eye/brain

MetamerismLight with different SPDs can appear the same

11

Direct LED Phosphor

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

380 430 480 530 580 630 680 730 780

Spec

tral

Pow

er (W

/nm

)

Wavelength (nm)

White Light from LEDsPhosphor Converted (PC)

Color Mixed (CM)

Hybrid (HY)

12

White Light from LEDsPhosphor Converted (PC)

Color Mixed (CM)

Hybrid (HY)

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

380 430 480 530 580 630 680 730 780

Spec

tral

Pow

er (W

/nm

)

Wavelength (nm)

RedLimeAmberGreenCyanBlueIndigo

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70

v'

u'

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

380 430 480 530 580 630 680 730 780

Spec

tral

Pow

er (W

/nm

)

Wavelength (nm)

Equal luminous flux, equal chromaticity

13

White Light from LEDsPhosphor Converted (PC)

Color Mixed (CM)

Hybrid (HY)

MetamerismLight with different SPDs can appear the same

14

White Light from LEDsPhosphor Converted (PC)

Color Mixed (CM)

Hybrid (HY)

0.00

0.01

0.02

0.03

0.04

0.05

380 430 480 530 580 630 680 730 780

Spec

tral

Pow

er (W

/nm

)

Wavelength (nm)

15

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

380 430 480 530 580 630 680 730 780

Rela

tive

Pow

er

Wavelength (nm)

Relative SPDs• Can be visually misleading• Can be used to calculate

CCT, Duv, chromaticity, color rendering

• Cannot be used to calculate luminous flux, melanopicflux, CS, damage, retinal hazard, PPF

16

0.00

0.01

0.02

0.03

0.04

0.05

380 430 480 530 580 630 680 730 780

Spec

tral

Pow

er (W

/nm

)

Wavelength (nm)

Absolute SPDs• Better for visual

comparison• Can be normalized to equal

flux (luminous, melanopic, photosynthetic)

• Can represent emitted light or light reaching a surface/point

17

SPD Data Transfer

Spreadsheet IES TM-27-14 (*.spdx) IES TM-33-18 (*.ies)(XML) (XML)(e.g., *.xlsx)

3. SPD-based Calculations

19

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

380 430 480 530 580 630 680 730 780

Rela

tive

Sens

itivi

ty

Wavelength (nm)

Φ=683*∫PλVλdλ

Photopic LuminousEfficiency Function, V(λ)

Used for:Lumens, lux, candela, luminous efficacy, LER

CIE 1931 Standard Photopic Observer (2°)

Note: Alternatives include the CIE 1964 Standard Observer (10°), among other visual efficiency functions.

20

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

380 430 480 530 580 630 680 730 780

Rela

tive

Sens

itivi

ty

Wavelength (nm)

Photopic V(λ)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

380 430 480 530 580 630 680 730 780

Rela

tive

Sens

itivi

ty

Wavelength (nm)

Erythropic Slc(λ)Chloropic Smc(λ)Cyanopic Ssc(λ)Melanopic Sz(λ)Rhodopic Sr(λ)

(Long Cone)

(Medium Cone)(Short Cone)

(ipRGC)

(Rod)

Photopic LuminousEfficiency Function, V(λ)

Used for:Lumens, lux, candela, luminous efficacy, LER

CIE 1931 Standard Photopic Observer (2°)

Note: Alternatives include the CIE 1964 Standard Observer (10°), among other visual efficiency functions.

21

=

=

=Area Area<Area Area

683*

683*

(Radiant Flux)

22

Luminous Flux (lm)

Luminous Efficacy of Radiation (LER)

=Radiant Flux (Wopt)

683*Area

Area

Area

LER =

Radiant Watts, Not Electrical Watts

=

LER = =683*Area

315 lm/Wradiant

154 lm/Wradiant

Spectral Efficiency

23

0.00

0.10

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0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

380 430 480 530 580 630 680 730 780

Rela

tive

Sens

itivi

ty

Wavelength (nm)

Max LER = 683 lm/W

LER is the maximum possible luminous efficacy if a light source is perfect at converting electrical watts to optical watts.

Realistic maximums are ~400 lm/W given chromaticity and color rendering limits.

24

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

380 430 480 530 580 630 680 730 780

Rela

tive

Sens

itivi

ty

Wavelength (nm)

y

z

x[V(λ)]

CIE 1931 Standard Colorimetric Observer (2°)

Note: Alternatives include the CIE 1964 Standard Colorimetric Observer (10°) and the cone fundamental-based tristimulus functions (CIE 15:2018)

Used for:Chromaticity, CCT, Duv

25

=

=

=

Area = Z

Area = Y

Area = X

Chromaticity Coordinates

X= X + Y + Z

Y= X + Y + Z

x

y

CIE 1931 (x, y)

4X= X + 15Y + 3Z

9X= X + 15Y + 3Z

u'

v'

CIE 1976 (u', v')

26

CIE 1931 (x, y) Chromaticity Diagram• Obsolete, but sill used by some• Not visually uniform (distance

doesn’t equal visual difference)

470475

480

485

490

495

500

505

510

515520

530540

550

560

570

580

590600

610620

700

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

y

x

Spectrum LocusPlanckian locus

Note: Colored background for orientation only.

27

CIE 1960 (u, v) Uniform Chromaticity Scale (UCS) Diagram• Obsolete, but sill used by some.• Intended to be visually uniform, but

isn’t (distance doesn’t equal visual difference)

0.0

0.1

0.2

0.3

0.4

0.5

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

v

uNote: Colored background for orientation only.

28

CIE 1976 (u', v') Uniform Chromaticity Scale (UCS) Diagram• Recommended for specifying

chromaticity/binning, consistency of chromaticity, chromaticity shift (color maintenance), chromaticity difference

• Δu'v' = chromaticity difference (between two products or over time)0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

v'

u'

Note: Colored background for orientation only.

29

0.26

0.28

0.30

0.32

0.34

0.36

0.38

0.16 0.18 0.20 0.22 0.24 0.26 0.28 0.30 0.32u

575 580570

585

CIE 1960 (u, v) Chromaticity Diagram (Obsolete) Correlated Color Temperature(CCT)

• Temperature of nearest Planckian radiator

• Approximately yellow-blue• Equal CCT does not equal

matching appearance

30

0.26

0.28

0.30

0.32

0.34

0.36

0.38

0.16 0.18 0.20 0.22 0.24 0.26 0.28 0.30 0.32u

575 580570

585

CIE 1960 (u, v) Chromaticity Diagram (Obsolete) Distance from Planckian Locus(Duv)

• Approximately purple-green• Equal CCT and Duv specifies

matching appearance for standard observer (real observers vary)

• Neutral white can cover a wide area

• Some preference for negative Duv at low CCTs?

+ Duv

- Duv

31

Consistency (of chromaticity)• Initial similarity in appearance• Addressed with binning

• ANSI/NEMA C78.377-2017

32

33

ANSI/NEMA C78.377-2017• Standard “7-Step” quadrangle bins

• plus 2200 K, 2500 K• DLC v5.0 Tier 2

• Extended “7-step” quadrangle bins• DLC v5.0 Tier 2

34

ANSI/NEMA C78.377-2017• Standard “7-Step” quadrangle bins

• plus 2200 K, 2500 K• DLC v5.0 Tier 2

• Extended “7-step” quadrangle bins• DLC v5.0 Tier 2

• Standard/Extended “4-step” quadrangle bins• DLC v5.0 Tier 1

• Flexible quadrangles, circles

35

0.518

0.519

0.520

0.521

0.522

0.247 0.248 0.249 0.250 0.251

v'

u'

12-75

Planckian locus

Sample 1

Sample 2

Sample 3

Sample 4

Sample 5

A

B

C

0.517

0.518

0.519

0.520

0.521

0.522

0.523

0.524

0.525

0.526

0.527

0.24

6

0.24

7

0.24

8

0.24

9

0.25

0

0.25

1

0.25

2

0.25

3

0.25

4

v'

u'

12-100

A

B

C

Chromaticity Maintenance (Over Time)

36

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.010

0 5,000 10,000 15,000 20,000 25,000

Chre

omat

icity

Shi

ft (Δ

u'v'

)

Hours of Operation

DLC v5.0 Tier 2

DLC v5.0 Tier 1

Cycled Samples End

37

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

380 430 480 530 580 630 680 730 780

Rela

tive

Sens

itivi

ty

Wavelength (nm)

Melanopic (M)

Blue Light Hazard

Luminous Efficiency (P)

z Color Matching (CCT)

Percent Blue

Scotopic (S) Blue Light / Circadian• One should not be used

to determine the other (e.g., CCT ≠ M or M/P)

• CS is not a weighting function.

4. Color Rendition

39https://doi.org/10.1146/annurev-vision-091718-015018

40

Past Method: CRI(CIE 13.3-1995)

New Method: TM-30(ANSI / IES TM-30-18)

8 Color Samples 99 Color SamplesMedium chroma/lightnessSpectral sensitivity varies

Uniform color space coverageSpectral sensitivity neutralVariety of real objectsMunsell samples only

1964 Color Vision Model 2006 Color Vision ModelColor difference inaccurateDistortion of red

Uniform color spaceImproved chromatic adaptation model

“Wrong” chromatic adaptation model Hue, chroma, lightness correlates

Limited Predictive Outputs Extensive Predictive OutputsAverage color difference (fidelity)Color fidelity for each color sample

Average color fidelity, gamut areaHue-specific (“local”) chroma shift, hue shift, fidelity

No indication of color shift directions Graphics, Spec Sheets, etc.

41

Type Name CriteriaVoluntary DesignLights Consortium Qualified Products List, V4.4 Ra ≥ 80Voluntary ENERGY STAR Certified Light Bulbs V2.0 Ra ≥ 80, R9 ≥ 0Voluntary (building certification) WELL Building Standard V2 Ra ≥ 90 OR Ra ≥ 80, R9 ≥ 50Mandatory (for sale in state) California Appliance Efficiency Regulations (Title 20) Ra ≥ 82Mandatory (residential new constr) California Building Efficiency Standards (Title 24 JA8) Ra ≥ 90, R9 ≥ 50Proposal Class A Ra ≥ 80, 80 ≤ GAI ≤ 100Recommendation IES Lighting Handbook, 10th Ed.

General InteriorColor AppraisalColor Matching & Reproduction

Ra ≥ 80Ra ≥ 85Ra ≥ 90

American National Standard Recommended Practice

ANSI/IES RP-1-12: Office LightingGeneralColor Matching/Discrimination

Ra ≥ 80Ra ≥ 90

American National Standard Recommended Practice

ANSI/IES RP-3-13: Educational FacilitiesGeneralColor Discrimination

Ra ≥ 80Ra ≥ 90

Recommended Practice IES RP-7-01: IndustrialImportantCritical

Ra ≥ 70Ra ≥ 85

Voluntary DesignLights Consortium Qualified Products List, V5.0 Ra ≥ 80, R9 ≥ 0; Ra ≥ 90, R9 ≥ 50

Color Rendition Specifications

42

Type Name CriteriaTier 1 Tier 2 Tier 3

Mandatory(military medical facilities)

U.S. DOD UFC 4-510-01: Design Military Medical Facilities Note: CRI alternative

Rf ≥ 78 (TM-30-15)97 ≤ Rg ≤ 110

-9% ≤ Rcs,h1 ≤ 9%Rf,h1 ≥ 78 (TM-30-15)

Voluntary (Building Certification)

WELL Building Standard V2 Note: CRI alternative

Rf ≥ 78Rg ≥ 98

-1% ≤ Rcs,h1 ≤ 15%

Rf ≥ 78Rg ≥ 98

-7% ≤ Rcs,h1 ≤ 15%

Draft ANSI/IES TM-30-18 Annex E/F“Color Preference”

Rf ≥ 78Rg ≥ 95

-1% ≤ Rcs,h1 ≤ 15%

Rf ≥ 74Rg ≥ 92

-7% ≤ Rcs,h1 ≤ 19%

Rf ≥ 70Rg ≥ 89

-12% ≤ Rcs,h1 ≤ 23%

Draft DesignLights Consortium Qualified Products List, V5.0Note: CRI alternative

Rf ≥ 78Rg ≥ 98

-1% ≤ Rcs,h1 ≤ 15%

Rf ≥ 70Rg ≥ 89

-12% ≤ Rcs,h1 ≤ 23%

43

Assumptions: • 200-700 lux• polychromatic environment• single chromaticity

DRAFT ANSI/IES TM-30-18 Annex E Table E.2

98

44

270 LUX

250 LUX

450 LUX

1. M. Royer, A. Wilkerson, M. Wei et al., “Human perceptions of colour rendition vary with average fidelity, average gamut, and gamut shape,” Lighting Research & Technology, 49(8), 966-991 (2016).2. M. Royer, A. Wilkerson, and M. Wei, “Human perceptions of colour rendition at different chromaticities,” Lighting Research & Technology, Online before print, DOI: 10.1177/1477153517725974 (2017).3. M. Royer, A. Wilkerson, M. Wei et al., “Experimental validation of color rendition specification criteria based on IES TM-30-18,” Draft. (2019).4. F. Zhang, H. Xu, and H. Feng, “Toward a unified model for predicting color quality of light sources,” Applied Optics,56(29), 8186-8195 (2017).5. T. Esposito, and K. Houser, “Models of colour quality over a wide range of spectral power distributions,” Lighting Research & Technology, Online Before Print. DOI: 10.1177/1477153518765953., (2018).

45

PNNL

Zhejiang

PSU

46

~165,000 SPDs• 2700 K to 6500 K• 0.006 to -0.018 Duv• Random spectral features• Full range of possibilities

Looks more like Daylight/Planckian(at equal illuminance)

Mor

e Vi

vid

Reds

Mor

e Du

ll Re

ds

47

Ra ≥ 80, R9 ≥ 0• Rf 41 – 100• Rcs,h1 -19% to 15%• DLC v5.0 Tier 2 Alternative

Why?• Bad models of color and vision• Different types of measures

Better spec?• Rf 65 – 100• Rcs,h1 -12% to 11%• DLC v5.0 Tier 1 Alternative

Why?• Bad models of color vision• Different types of measures

48

Experiments• Test perception of wide

range of characteristics• What do people like?

Find natural? Consider acceptable? Etc.

49

P1* Most Preferred• TM-30 P1* [DRAFT]• DLC v5.0 Tier 1• Most > 90% Acceptability

50

P1*

P2*

Also Preferred• TM-30 P2* [DRAFT]• Not in DLC• Most > 80% Acceptability

51

P1*

P2*

What’s on the market?• ~ 60% of products• ~ 80% of CRI ≥ 80 products

between 80 and 85

52

P1*

P2*

P3*

53

What’s on the market?• ~ 60% of products• ~ 80% of CRI ≥ 80 products

between 80 and 85• TM-30 P3* [DRAFT]• DLC v5.0 Tier 2• Most > 65% Acceptability

P1*

P2*

P3*

54

Outdoor?• Tier 3?• 98% of available products

with Ra ≥ 70

P1*

P2*

P3*

F1F2F3

Fidelity Spec (Rf & Rf,h1)• Alternative where design intent

is different

55

56

Thank Youmichael.royer@pnnl.gov