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What Next with the Candela What next with the candela 20th Meeting of the NMI Directors . Introduction of defining constant for photometry, Kcd luminous efficacy of monochromatic radiation of frequency 540 × 1012 Hz . Reformulation of definition of the candela ‐ (not a redefinition), to bring it in explicit constant form: www.bipm.org 2 Mole 71 Candela 79 Metre 83 2 1 3 Jeff Wall, Invisible Man Km Kcd The luminous efficacy of monochromatic 12 radiation of frequency 540 × 10 Hz, Kcd, is 683 lm/W. www.bipm.org 3 • Kcd makes a direct link between photometric and radiometric quantities for monochromatic radiation of frequency 540 THz flux illuminance intensity luminance lm ↔ W lx ↔ W∙m‐2 cd ↔ W∙sr‐1 cd∙m‐2 ↔ W∙sr‐1∙m‐2 Kcd Kcd Kcd Kcd • Mise en pratique for the definition of the candela in the SI (20 May 2019) • BIPM report 05/2019: Principles governing photometry (20 May 2019) • Appendix 3 Units for photochemical and photobiological quantities (20 May 2019) www.bipm.org 4 Photometry Kyle Bean – Interconnected senses Warhol, Marilyn www.bipm.org Monroe(1967) 5 Photometry Photometry is the science of the measurement of light, in terms of its perceived brightness to the human eye. To do photometry, you need : eyes brain light stimulus www.bipm.org 6 Photometry light source material light stimulus www.bipm.org 7 Measurement of perceptive quantities Challenge The measurand is not accessible by the measuring instrument Measurand Object www.bipm.org 8 Measurement of perceptive quantities Is stimulus 1 = stimulus 2 ? Stimulus Stimulus 1 2 www.bipm.org 9 Measurement of visual quantities Photometry deals with visual quantities. The measurand is not accessible by the measuring instrument The measurand may vary from an observer to another Visual quantity Object www.bipm.org 10 Vision and V() curve Human eye Lens Retina Fovea Rod Optical nerve Cone www.bipm.orgSource : ??? 1111 Vision and V() curve Cones (L M S) We have 3 family of cones. Light that reaches the retina generates 3 signals in the cones, that depend upon the wavelength S( ) L() Fundamentale sensitivity S() max 440 nm Sensibilité fondamentale Sensibilité M() M() max 540 nm L() max 570 nm 400 nm 700 nm www.bipm.org 1212 Vision and V() curve Individual variations We don’t have the same repartition of cones, but the visual system adjusts the sensitivity by adapting the gain Hofer, Carroll, Neitz, Neitz, Williams, JNeuroscience 2005 www.bipm.org 1313 Vision and V() curve CIE Photometric strandard observer 6th session of CIE, Geneva, 1924 K. S. Gibson : Visibility function 272 observers (UK, Japan, US) www.bipm.org 1414 Vision and V() curve CIE Photometric strandard observer V(λ) curve λmax = 555 nm 1,0 0,8 0,6 0,4 0,2 0 400 500555 600 700 (nm) www.bipm.org 15 Many agreed human visual response function (mesopic & 10°) www.bipm.org 16 Observers Female / Male Young / Old Naïve / Expert Colour blind? Vision corrected Morning / Afternoon ….. www.bipm.org 17 Photometry deals with visual quantities. The measurand is not accessible by the measuring instrument The measurand may vary from an observer to another Visual quantity Object www.bipm.org 18 The measurand may vary from an observer to an other Elaine Moynihan Lisle Miraï www.bipm.org Monet 19 Photometry describes the effects of visible light on the human eye, in terms of brightness and colour www.bipm.org 20 Towards the candela Visual comparisons What is the reference? UK Parliamentary Candle (1860) Extracted from “manipulation de physique” A. Leduc, 1895 1854 www.bipm.org 21 Towards the candela First standard Standard lamps Carcel Lamp Hefner Lamp Vernon Harcourt lamp © Cnam - Musée © PTB © NIST 1890 www.bipm.org 22 Towards the candela 1900 : the « black body », the ideal standard Radiance from the black body depends only of its temperature 2hc2 1 Lλ(λ,T) = λ5 e hc/(λkT) − 1 with : wavelength of the radiation T, black body temperature c, speed of light Photo collection particulière D. J. Lovell h, Planck constant Max Planck k, Boltzmann constant www.bipm.org 23 Towards the candela Freezing temperature of Platinium «“The candela is the luminous intensity, in the perpendicular direction, of a surface of 1/600 000 square metre of a black body at the temperature of freezing platinum under a pressure of 101 325 newtons per square metre.”» XIIIème CGPM, 1968 If the feezing platinum temperature varies, the radiation emitted by the black body varies and the candela varies !! Temperature [°C] 1775 0,23% 1770 1765 1940 1960 1980 2000 2020 years www.bipm.org 24 Radiometry, a new way for the candela Radiometry to rescue photometry Radiometry is the science of measurement of radiant energy (including light) in terms of absolute power. Radiometric techniques characterize the distributionoftheradiant power according to the wavelength. www.bipm.org 25 Radiometry, a new way for the candela LIGHT Electromagnetic waves with a wavelength between 380 nm and 780 nm 380 nm 780 nm Violet Blue Green Yellow Orange Red www.bipm.org 26 Radiometry, a new way for the candela Spectral power distribution of light sources Spectral power distribution describes the light spectrum of a light source It shows which radiations are present, at which wavelength, in which proportion. He‐Ne Laser White light source Power Power (W) (W) Wavelenght (nm) Wavelength (nm) www.bipm.org 27 Radiometry, a new way for the candela Progress in radiometry Radiometry allows measurement of 1,000% optical power at each wavelength 0,100% 0,010% 0,001% Relative standard uncertainty 1900 1920 1940 1960 1980 2000 2020 2040 2010 ‐> today www.bipm.org 28 Radiometry, a new way for the candela cryogenic radiometer 0,6 0,5 Absolute measurement on laser is good. 0,4 But transfer to incoherent light needs improvement 0,3 0,2 0,1 Dispersion and uncertainty / % 0 350 450 550 650 750 850 950 nm ‐0,1 www.bipm.org 29 Sensitivity curve of human eye www.bipm.org 30 Radiometry, a new way for the candela the new way… I [cd] E [lx] d I E = «The candela is the luminous intensity, in the 2 perpendicular direction, of a surface of T [K] d 1/600 000 square meter of a black body at the temperature of freezing platinum» 1948 : IXème CGPM www.bipm.org 31 Radiometry, a new way for the candela the new way… I [cd] diaphragm E [lx] S d P [W] I E = «The candela is the luminous intensity, in the 2 perpendicular direction, of a light source that d generates an illuminance of 1 lx at 1m distance, that is accessed by radiometry xxx : xxxème CGPM www.bipm.org 3232 Vision and V() curve CIE Photometric strandard observer V(λ) curve λmax = 555 nm 1,0 0,8 0,6 0,4 0,2 0 400 500555 600 700 (nm) www.bipm.org 33 Vision and V() curve V(λ) filter www.bipm.org 3434 1979, new definition and introduction of Km Introduction of Km I [cd] diaphragm S P [W] φ d2 I = S d φ [lm] P [W] 380 480 580 680 780 Wavelength (nm) www.bipm.org 35 1979, new definition and introduction of Km Introduction of Km I [cd] diaphragm S P [W] φ d2 I = S d φ [lm] P [W] P ⋅ V() dλ φ 380 480 580 680 780 Wavelenght (nm) www.bipm.org 36 1979, new definition and introduction of Km Introduction of Km I [cd] diaphragm S P [W] φ d2 I = S d φ [lm] P [W] P ⋅ V() dλ φ = Km [lm⋅W‐1] 380 480 580 680 780 Wavelength (nm) www.bipm.org 37 1979, new definition and introduction of Km Definition of the candela I [cd] Km P S d λmax «The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 THz and that has a radiant intensity in that direction of 1/683 watt per steradian» 1979 : XVIème CGPM www.bipm.org 38 Success story : Photometry Standard Photopic observer (CIE 1924) Luminous efficiency ‐1 Kcd = 638 lm⋅W 0 Luminous intensity 555 Wavelenght (nm) (visual) SI brochure Principle governing photometry www.bipm.org 39 What is missing New agreed human visual response function (mesopic and 10°) www.bipm.org 40 What is missing Challenge (1/2) The measurand is not accessible by the measuring instrument Measurand Object www.bipm.org 41 What is missing Challenge (2/2) The measurand may vary from one observer to an other Elaine Moynihan Lisle Le pont japonais, Giverny Miraï Monet www.bipm.org 42 Measurement of perceptive quantities Current method Radiometry & spectrophotometry Psychophysic Measurand experiments (perceptive) Standard observer Perception Normalization P ⋅ V() dλ model activity www.bipm.org 43 Measurement of perceptive quantities Future method RadiometryImage based & spectrophotometry radiometry PsychophysicMachine Measurand experimentsLearning (perceptive) Perceptive scale IndividualStandard Object observer (physical) Physical scale (measurable) Perception Artificial Normalization intelligencemodels activity www.bipm.org 44 The laser www.bipm.org 45 Cryogenic Radiometer Evacuation port Liquid helium Apertures : tank 5 mm 6 mm 7.5 mm Laser beam Brewster angle window Thermal screen International agreement and consistency Accuracy to SI <~0.01 % 100 ppm ur100 Kind courtesy of Armin Sperling, Armin PTB Kind courtesy of Transformative technology Invented in 60s in the USSR and the US Nobel prize to Basov, Prokhorov, Townes Was recognized as an amazing discovery “from science fiction” Was thought to be a useless “science toy”: “a solution looking for problem” www.bipm.org 49 From laser to WEB 2.0 Broad-band data transmission is enabled by fiber-optical communication Laser is a key component Dramatic impact on modern society in the past decade www.bipm.org 50 Manipulating single photons www.bipm.org 51 Second Quantum Revolution Ultrafast, “smart” computers Quantum internet (absolute security) Custom-designed quantum materials Quantum sensors Quantum-logic based standards www.bipm.org 52 Light sources 50/50 beamsplitter Correlation functions A Photo‐ g(2)(0)=1 : random, no correlation, ex.
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