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Introduction to Colorimetry

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Introduction to Colorimetry IES NY Issues in Color Seminar February 26, 2011 IntroductionIntroduction toto ColorimetryColorimetry JeanJean PaulPaul FreyssinierFreyssinier Lighting Research Center, Rensselaer Polytechnic Institute Troy, New York, U.S.A. sponsored by www.lrc.rpi.edu/programs/solidstate/assist 1 © 2010 Rensselaer Polytechnic Institute. All rights reserved. AcknowledgmentsAcknowledgments NYCNYC IESIES organizersorganizers ofof IssuesIssues inin ColorColor SeminarSeminar,, especiallyespecially ›› JasonJason Livingston,Livingston, WendyWendy LuedtkeLuedtke,, DanDan Rogers,Rogers, andand MegMeg SmithSmith LRCLRC faculty,faculty, staff,staff, andand studentsstudents SponsorsSponsors ofof ASSISTASSIST ProgramProgram 2 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Radiometry 3 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Radiometry Detection and measurement of electromagnetic energy › Purely physical – no consideration of how it stimulates the eye Unit of measurement: watt › The watt is a unit of power › Power is the rate of energy; energy per time • 1 watt = 1 joule/second 4 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Radiometry: Geometry and units The geometry of how radiant energy is produced, emitted, propagating, defines the units of measurement Description Quantity Unit Energy per time Power W Incident on a surface Irradiance W/m2 Leaving a surface Exitance W/m2 5 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Sources of radiance Sun Electroluminescent Approximate luminance, cd/m2 1.6x109 1.5x106 1.2x107 3.0x104 1.4x104 30 to to 1.0x109 3.9x107 High Medium Low 6 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Spectrum: Radiation as a function of wavelength The electromagnetic spectrum can be divided into smaller and smaller bands, or expressed as a continuous function of wavelength (or frequency) Units: W/nm P P d area under curve total 0 Daylight 5700 K Incandescent 1.0 1.0 0.9 0.9 0.8 0.8 0.7 0.7 0.6 0.6 power power 0.5 0.5 0.4 0.4 Relative 0.3 Relative 0.3 0.2 0.2 0.1 0.1 0.0 0.0 360 410 460 510 560 610 660 710 760 360 410 460 510 560 610 660 710 760 Wavelength (nm) Wavelength (nm) 7 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Spectra of typical light sources Incandescent Fluorescent High pressure sodium Light emitting diodes 1 1.2 1.2 6 1.0 1.0 5 0.8 0.8 4 energy 0.6 0.6 3 0.4 0.4 2 Relative Relative Energy Relative Energy 0.2 0.2 1 0 0.0 0.0 350 450 550 650 750 350 450 550 650 750 350 450 550 650 750 0 Wavelength(nm) Wavelength(nm) 390 440 490 540 590 640 690 740 Wavelength(nm) Wavelength (nm) 8 © 2010 Rensselaer Polytechnic Institute. All rights reserved. PhotometryPhotometry 9 © 2010 Rensselaer Polytechnic Institute. All rights reserved. What is photometry? A simple, mathematically precise system of measuring and specifying light agreed to by an international community involved with its commerce and specification 10 © 2010 Rensselaer Polytechnic Institute. All rights reserved. WhyWhy isis photometryphotometry important?important? PromotesPromotes internationalinternational tradetrade ProvidesProvides aa quantitativequantitative languagelanguage forfor communicatingcommunicating betweenbetween stakeholdersstakeholders 11 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Light IESNA Definition: Radiant energy capable of exciting the retina and producing a visual sensation. The visible portion of the electromagnetic spectrum extends from about 380 to 780 nanometers. CIE defines it over 360 to 830 nm. Official (CIE) definition: radiant energy weighted by the photopic luminous efficiency function, V(). Based on flicker photometry. 1 V(V()) -- PhotopicPhotopic V() - Scotopic 0.8 0.6 0.4 Luminous efficiency efficiency Luminous Luminous 0.2 0 300 350 400 450 500 550 600 650 700 750 800 Wavelength, nm 12 © 2010 Rensselaer Polytechnic Institute. All rights reserved. What does flicker photometry mean? Related to response of photoreceptors in central fovea › L and M cones Cone Fundamentals and V( ) › 2L + 1M V() 1 0.8 0.6 photopic L cone M cone 0.4 S cone relative value relative 0.2 0 400 500 600 700 wavelength (nm) 13 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Light: Calculation of luminous flux Fluorescent lamp, 4100 K (F32T8/841) 1.0 0.9 0.8 0.7 0.6 power 0.5 0.4 Relative 0.3 0.2 0.1 0.0 360 410 460 510 560 610 660 710 760 Wavelength (nm) 14 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Light: Calculation of luminous flux Fluorescent lamp, 4100 K (F32T8/841) 1.0 0.9 0.8 0.7 0.6 powerpower 0.5 0.4 Relative Relative 0.3 0.2 0.1 0.0 360 410 460 510 560 610 660 710 760 Wavelength (nm) 15 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Light: Calculation of luminous flux Fluorescent lamp, 4100 K (F32T8/841) 1.0 0.9 0.8 0.7 0.6 powerpower 0.5 0.4 Relative Relative 0.3 0.2 0.1 0.0 360 410 460 510 560 610 660 710 760 Wavelength (nm) 16 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Light: Calculation of luminous flux Fluorescent lamp, 4100 K (F32T8/841) 1.0 0.9 0.8 0.7 0.6 powerpower 0.5 0.4 Relative Relative 0.3 0.2 0.1 0.0 360 410 460 510 560 610 660 710 760 Wavelength (nm) 17 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Light: Calculation of luminous flux 830nm k P V d 380nm lm k 683 W P Power W V Photopic luminous efficiency function Luminous Flux 18 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Photometry Description Quantity Unit Light Luminous flux Lumen Amount incident per Illuminance Lumen/m2 surface area Amount leaving per (Luminous) Exitance Lumen/m2 surface area In a particular (Luminous) Intensity Lumen/sr direction (range of cd directions) In a direction, the Luminance Lumen/(m2 sr) amount emitted per cd/m2, nit surface area 19 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Photocell and photopic response CIE Photopic Luminous415 0.0022 Efficiency Function 420 0.393194 and Silicon 3.85E+02 4.0 Photocell420 Spectral 0.004 Response 430 0.407356 3.90E+02 4.3 1.0 425 0.0073 440 0.419748 3.95E+02 4.7 430 0.0116 450 0.434304 4.00E+02 5.0 435 0.0168 460 0.446499 4.05E+02 5.3 0.8 440 0.023 470 0.463415 4.10E+02 5.5 445 0.0298 480 0.476397 4.15E+02 5.7 0.6 450 0.038 490 0.487215 4.20E+02 5.9 455 0.048 500 0.500787 4.25E+02 6.1 0.4 460 0.06 510 0.512982 4.30E+02 6.3 465 0.0739 520 0.52439 4.35E+02 6.5 470 0.091 530CIE 0.536389 Photopic 4.40E+02 6.7 0.2 475 0.1126 540Silicon 0.548387 4.45E+02 7.0 480 0.139 550 0.560386 4.50E+02 7.2 0.0 485 0.1693 560 0.571597 4.55E+02 7.4 350 450 550490 650 0.208 750 570 850 0.583202 950 4.60E+02 1050 7.6 495Wavelength 0.2586 (nm) 580 0.594611 4.65E+02 7.8 500 0 323 590 0 606412 4 70E+02 81 20 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Errors applying V() Filters work well for broadband, “white” light sources, but not for narrowband sources Illuminance Meter 0.3 CIE Photopic Illuminance Meter 0.25 CIE Photopic 1 0.2 Blue LED 0.8 0.15 Relative response Relative 0.1 0.6 0.05 0.4 Relative response Relative 0 440 450 460 470 480 490 500 Wavelength (nm) 0.2 0 400 450 500 550 600 650 700 Wavelength (nm) 21 © 2010 Rensselaer Polytechnic Institute. All rights reserved. ColorimetryColorimetry 22 © 2010 Rensselaer Polytechnic Institute. All rights reserved. WhatWhat isis color?color? PerceptionPerception –– opponentopponent colorcolor theorytheory › Red vs. green › Blue vs. yellow › Hue › Saturation (chroma) › Lightness (brightness) ColorColor matchingmatching –– trichromatictrichromatic colorcolor theorytheory › Any light can be perfectly matched with a combination of just 3 standard lights SpecificationSpecification ofof thethe lightlight stimulusstimulus › Color matching functions › Equivalent to photometry 23 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Human color perception Trichromatic vision › 3 cone photoreceptors › Overlapping spectral sensitivity › A lot of not completely understood neural processing both at the retina and within the visual cortex of the brain 24 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Opponent color encoding 25 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Metamers Lights of the same color appearance can be made up of different spectral power distributions as seen in the diagram at the right. Sources with the same color appearance, but different spectral power distributions will render colors differently. Broad spectral power distributions are more likely to produce better color rendering These three spectra can produce the same color perception 26 © 2010 Rensselaer Polytechnic Institute. All rights reserved. Metamers -4 x 10 1 0.9 Yellow-filteredYellow LED incandescent 0.8 YellowYellow-filtered LED white source 0.7 0.6 0.5 0.4 0.3 Spectral Power, W/nm Power, Spectral 0.2 0.1 0 400 450 500 550 600 650 700 Wavelength, nm 27 © 2010 Rensselaer Polytechnic Institute. All rights reserved. CIE colorimetric system Based on color matching – not color perception Principle of univariance › Once a photon is absorbed by a photoreceptor all wavelength information is lost › Photoreceptor response is determined by the number of photons absorbed › Color information is contained in the relative strength of the signals from each type of photoreceptor Matching done under very particular and controlled conditions › 2° observer and 10° observer › Bipartite field Reference Matching field field 28 © 2010 Rensselaer Polytechnic Institute.
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