chromaticity adrift: understanding led color stability … · · 2015-05-11chromaticity adrift:...
TRANSCRIPT
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Michael Royer, PNNL
May 4–7, 2015
Lightfair
Chromaticity Adrift: Understanding LED Color Stability
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What metrics are used to describe color shift/color stability?
A
B
C D
1-step
2-step
3-step
MacAdam Ellipses
• Experimentally-derived indicators of human color vision tolerances at various chromaticities
• Based on the observations of one highly-trained observer in a very specific scenario/apparatus; results cannot be translated to every installation
• Sometimes referred to as SDCM (standard deviation of color matching)
• Can be reported in multiples (e.g., 3-step ellipse)
• Do not convey the direction of shift/difference
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0.510
0.515
0.520
0.525
0.530
0.535
0.540
0.250 0.255 0.260 0.265 0.270
v'
u'
Δu'v'
• Δu'v' is the Euclidian distance between two sets of chromaticity coordinates in the CIE 1976 UCS chromaticity diagram.
• As with MacAdam Ellipses, Δu'v' does not convey the direction of a shift
• Δu'v' does not convey whether or not a difference is noticeable
What metrics are used to describe color shift/color stability?
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0.44
0.45
0.46
0.47
0.48
0.49
0.50
0.51
0.52
0.53
0.54
0.55
0.56
0.16 0.17 0.18 0.19 0.20 0.21 0.22 0.23 0.24 0.25 0.26 0.27 0.28 0.29 0.30
v'
u'
Δu'v'
r = 0.007
7-step MacAdam Ellipses For CFLs ANSI C78.376-2001 SSL Quadrangles ANSI C78.377-2011
Iso-CCT (±0.02 Duv)
Daylight Locus
Black Body Locus
• MacAdam ellipses are approximately circles in the 1976 (u', v') chromaticity diagram
• A 1-step ellipse is approximately equal to a Δu'v' of 0.001
• ANSI definitions of white light allow for fairly large tolerances (~14-step difference from edge to edge)
What metrics are used to describe color shift/color stability?
Δu'v' and MacAdam Ellipses
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When does color shift become noticeable?
The million dollar question…
It depends.
Viewer
Field of View
Surface Characteristics
Proximity Time
In MacAdam’s experimental setup, a just noticeable difference was determined to be three times the standard deviation of color matching (or a 3-step ellipse) for a given observer. However, a 1-step ellipse is often called a MacAdam unit of color difference.
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Is color shift a problem for LEDs?
CALiPER
c. 2008
0.44
0.46
0.48
0.50
0.52
0.54
0.18 0.20 0.22 0.24 0.26 0.28
v'
u'
7
4
ANSI C78.377-2011 chromaticity bins
Black body locus
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Is color shift a problem for LEDs?
F4
Avg.
C12 A12
Q7
0.0000
0.0010
0.0020
0.0030
0.0040
0.0050
0.0060
0.0070
0 5,000 10,000 15,000 20,000 25,000
Δu
'v'
Hours of Operation
L Prize
LED A19 c. 2009
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Is color shift a problem for LEDs?
GATEWAY Smithsonian
LED PAR38 c. 2011
Image Courtesy of Scott Rosenfeld, Smithsonian American Art Museum
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Is color shift a problem for LEDs?
New 4,000
0.510
0.515
0.520
0.525
0.530
0.535
0.540
0.240 0.245 0.250 0.255 0.260 0.265 0.270
v'
u'
New
4,000
0.510
0.515
0.520
0.525
0.530
0.535
0.540
0.240 0.245 0.250 0.255 0.260 0.265 0.270
v'
u'
B1 B2
Bare Lamp Bare Lamp with Secondary Optics Removed
GATEWAY Smithsonian
LED PAR38 c. 2011
7 4
7 4
10
Is color shift a problem for LEDs?
GATEWAY Smithsonian
LED PAR38 c. 2011
Image Courtesy of Scott Rosenfeld, Smithsonian American Art Museum
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Is color shift a problem for LEDs?
GATEWAY Smithsonian
LED PAR38 c. 2011
Image Courtesy of Scott Rosenfeld, Smithsonian American Art Museum
12
Is color shift a problem for LEDs?
http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/2013_gateway_color-maintenance.pdf
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Is color shift a problem for LEDs?
0.0000
0.0010
0.0020
0.0030
0.0040
0.0050
0.0060
0.0070
0 2,000 4,000 6,000 8,000 10,000 12,000 14,000
Δu
'v'
Hours
LED
CFL
Halogen
CMH
CALiPER Series 20
LED PAR38 c. 2012
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Is color shift a problem for LEDs?
0.000
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0 2,000 4,000 6,000 8,000 10,000 12,000 14,000
Δu
'v'
Hours
CALiPER Series 20
LED PAR38 c. 2012
Most lamps rated
lifetime = 50,000 hrs
16
Is color shift a problem for LEDs?
0.000
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000
Δu
'v'
Hours
LED
CFL
Halogen
CALiPER Retail 3
LED A19 c. 2013
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Is color shift a problem for LEDs?
0.000
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000
Δu
'v'
Hours
CALiPER Retail 3
LED A19 c. 2013
Most lamps rated
lifetime = 25,000 hrs
18
Is color shift a problem for LEDs?
Parametric failure criterion (0.007)
0.000
0.005
0.010
0.015
0.020
0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000
Δu
'v'
Hours
CALiPER Retail 3
LED A19 c. 2013
Most lamps rated
lifetime = 25,000 hrs
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Is color shift a problem for LEDs?
U.S. Border
LED Area Lighting c. 2014
0.49
0.50
0.51
0.52
0.21 0.22 0.23 0.24
v'
u'
LM-79 Test Data (Spec)
2,500 Hour In-Situ (Field)
5,000 Hour In-Situ (Field)
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4
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What to do?
• LED Packages
• Lamp and Luminaire Materials (Optics)
• Driver
• Application considerations
• HEAT!
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What to do?
• Determine if color shift is a concern, and to what degree. – Will early failures be a financial concern?
– Is mitigation possible?
• Seek data (LM-80, LM-84 are only current relevant standards)
• Look for products with a warranty (there are few) – Understand what monitoring/measurement is
necessary