Post on 12-May-2018
transcript
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November 2014
Agenda
• Light and Color: Understanding the Basics
• Color Rendering Index for White Light Sources
• Methods for Creating White Light with LEDs
• New Techniques For Achieving High CRI
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November 2014
…and to accent the rich color which abounds in nature, interior design, clothing and fabric, jewelry, etc., while giving product and lighting designers the new lighting resources to continue to evoke emotional responses to lit environments.
High Color Rendering from LEDs play an important role in satisfying the light quality needs of end users
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November 2014
IESNA Definition: A pictorial
representation of the radiant power
emitted by a light source at each
wavelength or band of wavelengths
in the visible region of the
electromagnetic spectrum (360 to
770 nanometers).
SPD plots for several common light
sources showing relative radiate
power as a function of wavelength.
– Gold: High Pressure Sodium
– Blue: CIE D65, model of “average
daylight” at 6504K
– Red: Incandescent (3000K)
– Green: LED (6000K)
Spectral Power Distribution (SPD)
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IESNA Definition: the absolute
temperature of a blackbody
whose chromaticity most
nearly resembles that of the
light source.
The correlated color temperature
(CCT) designation for a light
source gives a good indication
of the lamp's general
appearance, but does not give
information on its specific
spectral power distribution.
Therefore, two lamps may
appear to be the same color,
but their effects on object
colors can be quite different.
Correlated Color Temperature (CCT)
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Color Rendering Index Ra
• The color rendering index describes how naturally a light source displays a set of
different test colors.
• Reference and test light sources are calculated at the same CCT, measuring shift in
chromaticity.
• Lamps that render color samples similarly will have a high CRI.
• The lower the CRI, the higher the luminous efficacy (lm/W) of an LED.
#1#2
#3 #4#5
#6
#8
#7
Color Rendering Index
A measure of the degree of color shift objects undergo when
illuminated by the light source as compared with the color of those
same objects when illuminated by a reference source.
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Reference Illuminants (Light Sources)
CRI measures the degree of color shift objects undergo when illuminated by the light
source as compared with the color of those same objects when illuminated by a
reference source of the same Correlated Color Temperature.
Black Body Radiator:
Color Temperatures in
the range of
2300K … < 5000K
Daylight Spectrum:
Color Temperatures
in the range of
5000K … 25000K
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Color Rendering Index Ra
• Additional six special test color samples
#1#2
#3 #4#5
#6
#8
#13
#11#10
#9
#14
#7
#12
Color Rendering Index
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November 2014
CRI 50
8500K
Color Rendering Index (CRI)
Example
CRI 70
5000K
CRI 95
3500K
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November 2014
Color Quality
Rating of Color Rendering Index
Definition of Color Rendering Classes for Color Quality
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November 2014
Color Quality – Industry Ratings
Energy Star
• SSL Indoor Luminaires:
CCT: 2700, 3000, 3500, 4000/4100K and 5000K for commercial
CRI: Ra ≥80
• SSL Indoor Lamps:
CCT: 2700, 3000, 3500, 4000/4100K and 5000K
CRI: Ra ≥80, R9>0
Designlights Consortium (DLC)
• Based on lighting application
Application Minimum Light Output
Minimum
Luminaire
Efficacy
Allowable CCTs
(ANSI C78.377-
2008) Minimum CRI
Outdoor Pole/Arm-Mounted Area and Roadway Luminaires 1,000 lm 60 lm/W <5700K 50
Linear Panels (2x2 Troffers) 3,000 lm 60 lm/W <5000K 80
Four-foot Linear Replacement Lamps 2,200 lm 96 lm/W <5000K 80, R9>0
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November 2014
Limitations of CRI
• Small number of color samples, which are unsaturated.
– Test color samples 9-12 are for saturated colors, but they do not contribute to the computation of general CRI.
• CRI does not reasonably characterize highly structured, narrowband spectral emissions like those from SSL sources (red, green, and blue components) which may increase or decrease saturation of certain colors.
• One number cannot tell you everything. Cannot fully characterize the multidimensional experience of color such as color appearance, color fidelity, chromatic discrimination, vividness and observer preferences.
• Mock-ups remain the recommended method of assessing lamp color rendering properties, particularly in color critical applications.
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Limitations of CRI
Example
• Same Chromaticity
• Same CCT
• Different CRI
• Different illumination
• lumens = 217
• CCT = 3231
• x = 0.4217 y = 0.3987
• D(uv) = 0.0002
• CRI=1
• lumens = 31.2
• CCT = 3223
• x = 0.4217 y = 0.3978
• D(uv) = -0.0002
• CRI=94
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November 2014
New Metrics – Color Quality Scale (CQS) (CIE TC1-69)
• Developed at the National Institute of Standards and Technology (NIST) to define and better qualify LED lighting.
• CQS involves several facets of color quality, including: color rendering, chromatic discrimination, and observer preferences.
• Main differences from CRI:
– Takes into account subjective color saturation perception - Gives weight to an increase of saturation addressing perception
– Measures color fidelity with regard to color saturation preferences
– Moderate increase of saturation is often correlated with desired color perception.
• Identifies color fidelity but is only one number!
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November 2014
New Metrics – CRI / Gaumut Area Index (GAI)
www.lrc.rpi.edu/programs/solidstate/assist/recommends/lightcolor.asp
• Developed by ASSIST program to give subjective assessments of vividness, naturalness and acceptability.
• CRI and CRI-like metrics only evaluate a single aspect: fidelity.
• Good color rendering by a light source requires an optimum amount of color saturation. Gamut area index (GAI) is a good indicator of saturation.
– This two-metric recommendation using CRI and GAI together can ensure good color rendering.
Results are representative of observers
of different geographical origins and for
sources of warm and cool CCTs,
different spectral makeup, and light level.
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November 2014
LED Spectrum is Critical for Interior Design
Color Temperature (CCT) is not a
perfect measure of lighting quality
Color rendering index is another
imperfect lighting quality metric, with
its emotional impact dependent on the
interaction of the illuminated surfaces
Lighting spectrum, material textures and
optical property interactions influence
interior design results
Managing the LED color spectrum can
create varied emotions from “sterile /
clean to soft / warm”
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November 2014
• Entire white CCT-range (2700-6500K)
LED Phosphors
LCW.CCCRI95
2700-4000K
LCW.ECCRI82
2700-5000K
LCW.PCCRI70
4000-5000K
LUWCRI70
5500-6500K
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November 2014
Traditional Light Sources
Fluorescent
CCT: 3000K
CRI: 85
High Pressure Sodium
CCT: 1800-2200K
CRI: ~20
Tungsten Halogen
3000K
CRI: ~95-100
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November 2014
Lighting Technologies - The LED Advantage
LEDs are an energy-saving alternative to conventional incandescent bulbs
LEDs are point source emitters with precise optical control
No radiated heat, only conducted.
LEDs are available in all saturated and unsaturated colors
LEDs are “instant on-off” and can be precisely controlled
150 Im/W9 Im/W
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• Typical CRI of 95
• R9 > 90
• R13 >90
• 2700-4000K
• Indoor Lighting
• Retail Lighting
Phosphor-based High CRI
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Phosphor-based High CRI
Warm white (3000K) LED with a typical CRI Ra = 95 and very good R9 and R13 values.
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With standard white LEDs it is not possible to realize LED luminaires
and lamps with both high efficiencies and high CRI.E
ffic
ien
cy o
n l
um
ina
ire
le
ve
l (l
m/W
)
The Efficiency and CRI Dilemma
*Luminaire efficiency considers thermal,
optical and electrical losses
Color Rendering and Luminaire Efficiency*
With the Brilliant Mix concept, high CRI and high efficiencies can be realized!
Brilliant Mix Solution
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November 2014
• Mix of EQ White and Amber LEDs
• High efficacy and high CRI with Ra > 90
• Efficacies of >110 lm/W possible (2700K – 4000K) at LED level
Hybrid Approach - High CRI LEDs
Brilliant Mix Concept
“Brilliant Mix” - Mixing of EQ White and Amber/Red LEDs results in warm
white light...with a high CRI and a high luminous efficacy.
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November 2014
• Mixing of EQ White and amber
LEDs enables warm
white light sources.
Brilliant Mix Concept
Combination of EQ White
and Amber LEDs results
in efficient light with a
high CRI
Hybrid Approach - High CRI LEDs
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November 2014
Combination of Amber (617nm) and EQ White
Brilliant Mix Example
Hybrid Approach - High CRI LEDs
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November 2014
Hybrid Approach - High CRI LEDs
Spectral Power Distribution
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November 2014
Hybrid Approach - High CRI LEDs Brilliant Mix concept – R values (2700K)
CCT: 2700K
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November 2014
OSLON SSL LED
Compact and symmetrical with high luminosity
Integrated silicone lens
Excellent thermal management
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November 2014
New LED Concepts
Color tunable white
Highly efficient, high CRI, white color tuning
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November 2014
Summary
• CRI is the current way of describing a light’s ability to render color.
• New metrics are being developed.
• New research and development is ongoing to improve LED color rendering and efficacy.
• LED sources can truly compete today for color critical applications.
• OSRAM continues to lead the way in developing LEDs with superior high color rendering
for every lighting application.
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November 2014
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