Chromaticity Adrift: Understanding LED Color Stability Michael Royer, PNNL Lightfair May 4–7, 2015 1 What metrics are used to describe color shift/color stability? MacAdam Ellipses • Experimentally-derived indicators of human color vision tolerances at various chromaticities 1-step • Based on the observations of one 2-step highly-trained observer in a very 3-step specific scenario/apparatus; results A cannot be translated to every C D installation • Sometimes referred to as SDCM (standard deviation of color B matching) • Can be reported in multiples (e.g., 3- step ellipse) • Do not convey the direction of shift/difference 2 What metrics are used to describe color shift/color stability? 0.540 Δu'v' • Δu'v' is the Euclidian distance 0.535 between two sets of chromaticity coordinates in the CIE 1976 UCS 0.530 chromaticity diagram. • As with MacAdam Ellipses, Δu'v' does not convey the direction of a shift v' 0.525 • Δu'v' does not convey whether or not a difference is noticeable 0.520 0.515 0.510 0.250 0.255 0.260 0.265 0.270 u' 3 What metrics are used to describe color shift/color stability? Δu'v' and MacAdam Ellipses 0.56 • MacAdam ellipses are 0.55 Black Body Δu'v' Locus r = 0.007 approximately circles in 0.54 the 1976 (u', v') 0.53 Iso-CCT (±0.02 Duv) chromaticity diagram 0.52 • A 1-step ellipse is 0.51 approximately equal to a Δu'v' of 0.001 v' 0.50 • 0.49 ANSI definitions of white light allow for 0.48 7-step MacAdam Ellipses fairly large tolerances For CFLs 0.47 ANSI C78.376-2001 (~14-step difference 0.46 SSL Quadrangles from edge to edge) Daylight ANSI C78.377-2011 0.45 Locus 0.44 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 u' 4 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. 5 Is color shift a problem for LEDs? CALiPER c. 2008 0.54 4 7 0.52 0.50 ' v 0.48 0.46 ANSI C78.377-2011 chromaticity bins Black body locus 0.44 0.18 0.20 0.22 0.24 0.26 0.28 6 u' Is color shift a problem for LEDs? L Prize LED A19 c. 2009 0.0070 0.0060 0.0050 0.0040 u'v' Δ 0.0030 F4 0.0020 Avg. 0.0010 Q7 C12 A12 0.0000 0 5,000 10,000 15,000 20,000 25,000 Hours of Operation 7 Is color shift a problem for LEDs? GATEWAY Smithsonian LED PAR38 c. 2011 Image Courtesy of Scott Rosenfeld, Smithsonian American Art Museum 8 Is color shift a problem for LEDs? GATEWAY Smithsonian LED PAR38 c. 2011 B1 0.540 B2 0.540 0.535 0.535 4,000 0.530 0.530 ' ' v v New 0.525 4,000 0.525 New 4 4 0.520 7 0.520 7 0.515 0.515 0.510 0.510 0.240 0.245 0.250 0.255 0.260 0.265 0.270 0.240 0.245 0.250 0.255 0.260 0.265 0.270 u' u' Bare Lamp Bare Lamp with Secondary Optics Removed 9 Is color shift a problem for LEDs? GATEWAY Smithsonian LED PAR38 c. 2011 Image Courtesy of Scott Rosenfeld, Smithsonian American Art Museum 10 Is color shift a problem for LEDs? GATEWAY Smithsonian LED PAR38 c. 2011 Image Courtesy of Scott Rosenfeld, Smithsonian American Art Museum 11 Is color shift a problem for LEDs? http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/2013_gateway_color-maintenance.pdf 12 13 Is color shift a problem for LEDs? CALiPER Series 20 LED PAR38 c. 2012 0.0070 0.0060 0.0050 0.0040 u'v' Δ 0.0030 0.0020 LED CFL 0.0010 Halogen CMH 0.0000 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 Hours 14 Is color shift a problem for LEDs? CALiPER Series 20 LED PAR38 c. 2012 0.007 0.006 0.005 0.004 u'v' Δ 0.003 0.002 0.001 0.000 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 Hours Most lamps rated lifetime = 50,000 hrs 15 Is color shift a problem for LEDs? CALiPER Retail 3 LED A19 c. 2013 0.007 LED 0.006 CFL Halogen 0.005 0.004 u'v' Δ 0.003 0.002 0.001 0.000 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 Hours 16 Is color shift a problem for LEDs? CALiPER Retail 3 LED A19 c. 2013 0.007 0.006 0.005 0.004 u'v' Δ 0.003 0.002 0.001 0.000 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 Hours Most lamps rated lifetime = 25,000 hrs 17 Is color shift a problem for LEDs? CALiPER Retail 3 LED A19 c. 2013 0.020 0.015 u'v' 0.010 Δ Parametric failure criterion (0.007) 0.005 0.000 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 Hours Most lamps rated lifetime = 25,000 hrs 18 Is color shift a problem for LEDs? U.S. Border LED Area Lighting c. 2014 19 Is color shift a problem for LEDs? U.S. Border 0.52 LED Area Lighting c. 2014 LM-79 Test Data (Spec) 0.51 2,500 Hour In-Situ (Field) 5,000 Hour In-Situ (Field) ' v 4 0.50 7 0.49 0.21 0.22 0.23 0.24 u' 20 Is color shift a problem∆u'v' = 0.006for LEDs? Smithsonian (Again) 21 What to do? • LED Packages • Lamp and Luminaire Materials (Optics) • Driver • Application considerations • HEAT! 22 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 23 .