Light and Color Methods of Achieving High CRI with LEDs
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 OSRAM High CRI LED Page 2
High Color Rendering from LEDs play an important role in satisfying the light quality needs of end users 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. OSRAM High CRI LED Page 3
LIGHT COLOR AND QUALITY Understanding the Basics OSRAM High CRI LED Page 4
Nature of Light: Illumination and Sensing OSRAM High CRI LED Page 5
Spectral Power Distribution (SPD) 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) OSRAM High CRI LED Page 6
Correlated Color Temperature (CCT) 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. OSRAM High CRI LED Page 7
COLOR RENDERING INDEX For White Light Sources OSRAM High CRI LED Page 8
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. Color Rendering Index R a 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. # 8 # 1 # 2 # 3 # 4 # 5 # 6 # 7 OSRAM High CRI LED Page 9
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 OSRAM High CRI LED Page 10
Color Rendering Index Color Rendering Index R a Additional six special test color samples # 8 # 1 # 2 # 3 # 4 # 5 # 6 # 7 # 14 # 13 # 9 # 10 # 11 # 12 OSRAM High CRI LED Page 11
Color Rendering Index (CRI) Example CRI 50 8500K CRI 70 5000K CRI 95 3500K OSRAM High CRI LED Page 12
Color Quality Rating of Color Rendering Index Definition of Color Rendering Classes for Color Quality OSRAM High CRI LED Page 13
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 OSRAM High CRI LED Page 14
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. OSRAM High CRI LED Page 15
Limitations of CRI Example Same Chromaticity Same CCT Different CRI Different illumination lumens = 31.2 CCT = 3223 x = 0.4217 y = 0.3978 D(uv) = -0.0002 CRI=94 lumens = 217 CCT = 3231 x = 0.4217 y = 0.3987 D(uv) = 0.0002 CRI=1 OSRAM High CRI LED Page 16
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! OSRAM High CRI LED Page 17
New Metrics CRI / Gaumut Area Index (GAI) 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. OSRAM High CRI LED Page 18 www.lrc.rpi.edu/programs/solidstate/assist/recommends/lightcolor.asp
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 OSRAM High CRI LED Page 19
METHODS OF CREATING White Light With LEDs OSRAM High CRI LED Page 20
How Do You Generate White Light? OSRAM High CRI LED Page 21 New Innovative Approaches
How Do LEDs Work? OSRAM High CRI LED Page 22
LED Phosphors OSRAM High CRI LED Page 23
LED Phosphors Entire white CCT-range (2700-6500K) LCW.CC CRI95 2700-4000K LCW.EC CRI82 2700-5000K LCW.PC CRI70 4000-5000K LUW CRI70 5500-6500K OSRAM High CRI LED Page 24
LED CCT Variations CRI 95 CRI 70 CRI 80 OSRAM High CRI LED Page 25
Traditional Light Sources Fluorescent CCT: 3000K CRI: 85 High Pressure Sodium CCT: 1800-2200K CRI: ~20 Tungsten Halogen 3000K CRI: ~95-100 OSRAM High CRI LED Page 26
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 9 Im/W 150 Im/W OSRAM High CRI LED Page 27
New Techniques For Achieving High CRI OSRAM High CRI LED Page 28
Phosphor-based High CRI Typical CRI of 95 R9 > 90 R13 >90 2700-4000K Indoor Lighting Retail Lighting OSRAM High CRI LED Page 29
Phosphor-based High CRI Warm white (3000K) LED with a typical CRI R a = 95 and very good R 9 and R 13 values. OSRAM High CRI LED Page 30
Efficiency on luminaire level (lm/w) The Efficiency and CRI Dilemma With standard white LEDs it is not possible to realize LED luminaires and lamps with both high efficiencies and high CRI. With the Brilliant Mix concept, high CRI and high efficiencies can be realized! Color Rendering and Luminaire Efficiency* Brilliant Mix Solution *Luminaire efficiency considers thermal, optical and electrical losses OSRAM High CRI LED Page 31
Hybrid Approach - High CRI LEDs Brilliant Mix - Mixing of EQ White and Amber/Red LEDs results in warm white light...with a high CRI and a high luminous efficacy. Brilliant Mix Concept Mix of EQ White and Amber LEDs High efficacy and high CRI with R a > 90 Efficacies of >110 lm/w possible (2700K 4000K) at LED level OSRAM High CRI LED Page 32
Hybrid Approach - High CRI LEDs Brilliant Mix Concept Mixing of EQ White and amber LEDs enables warm white light sources. Combination of EQ White and Amber LEDs results in efficient light with a high CRI OSRAM High CRI LED Page 33
Hybrid Approach - High CRI LEDs Brilliant Mix Example Combination of Amber (617nm) and EQ White OSRAM High CRI LED Page 34
Hybrid Approach - High CRI LEDs Spectral Power Distribution OSRAM High CRI LED Page 35
Hybrid Approach - High CRI LEDs Brilliant Mix concept R values (2700K) CCT: 2700K OSRAM High CRI LED Page 36
OSLON SSL LED Compact and symmetrical with high luminosity Integrated silicone lens Excellent thermal management OSRAM High CRI LED Page 37
New LED Concepts Color tunable white Highly efficient, high CRI, white color tuning OSRAM High CRI LED Page 38
Summary OSRAM High CRI LED Page 39
LED Source Measureables + + OSRAM High CRI LED Page 40
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. OSRAM High CRI LED Page 41
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