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
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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
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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
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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
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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