From Candle to Candela Yuqin Zong Sheds Light on Photometry’S Fundamental Unit

Total Page:16

File Type:pdf, Size:1020Kb

From Candle to Candela Yuqin Zong Sheds Light on Photometry’S Fundamental Unit measure for measure From candle to candela Yuqin Zong sheds light on photometry’s fundamental unit. he candela (cd), the unit of luminous the average human eye for specified visual steps need to be taken to redefine the candela intensity, is the International System of conditions (photopic, scotopic and mesopic based on fundamental quanta (photons) TUnits (SI) base unit for photometry — vision). Using the definition of the candela to meet the increasing needs of quantum the science of measuring light as perceived and the CIE spectral luminous efficiency photometric and radiometric measurements. by the human eye. The standards used for functions, the luminous intensity of any This view also expresses that human vision is defining and measuring luminous intensity, light source can be obtained. photon-based — the interaction of photons a measure of the luminous power emitted In 2009, in response to advances in with photoreceptor molecules in the eye. by a light source, in a particular direction, quantum-based optical technologies and In the end, there was no unanimous per steradian, have evolved along with their emerging metrological applications, agreement within the CCPR concerning the the development of technologies and the Consultative Committee for Photometry 2009 proposal, and it was ultimately rejected. It application needs, from candles, gas lamps and Radiometry (CCPR) proposed to is still unclear whether the ongoing debate on and incandescent lamps to Planck radiators. add the following explanatory text to the the explanatory text for the reformulation of The candela was first defined in 1948, and reformulation of the candela2: “Thus we have the candela will eventually reach a consensus reformulated in 1967 as “the luminous the exact relation Kcd = 683 lm/W. The effect and whether a redefinition of the candela intensity, in the perpendicular of this definition is that the candela is based on photons will be considered in the direction, of a surface of the luminous intensity, in a given near future. Meanwhile, the CCPR decided 1/600,000 square meter of a Y direction, of a source that emits to include photon-number-based quantities M A black body at the temperature L monochromatic radiation of (for example, photon intensity, photon flux A 12 / of freezing platinum under a frequency 540 × 10 hertz and and photon irradiance) and their realizations K C pressure of 101,325 newtons O that has a radiant intensity in in the recently published mise en pratique — T S per square meter.” R that direction of 1/683 watt guidelines on how the candela and its related E P 4 U Subsequent advances in S per steradian. This radiant units can be realized in practice . radiometry (the measurement © intensity corresponds to a In any event, Kcd is the new defining of optical radiation power) photon intensity of (683 × 540 × constant for photometry, without uncertainty, brought new capabilities to the field 1012 × 6.62606896 × 10−34)−1 photons representing the luminous efficacy of of photometry, offering alternative ways per second per steradian.” (The constant monochromatic radiation of frequency 12 to realize the candela in addition to using Kcd involves the lumen (lm = cd sr), the unit 540 × 10 hertz, and is recommended by high-temperature Planck radiators, which are of luminous flux, a measure for the total the CCPR to be one of the seven defining expensive and difficult to operate. Therefore, amount of visible light emitted from a source. constants used to scale the entire SI system3,5. in 1979, the current definition of the candela The unit ‘photons per second per steradian’ is A new SI brochure on the definitions was adopted1: “The candela is the luminous used for photon intensity.) The last sentence of the SI units is now being prepared and intensity, in a given direction, of a source that of the explanatory text, which did not alter in is expected to be published in 2018, with emits monochromatic radiation of frequency any way the current definition of the candela, a definition of the candela adjusted to the 540 × 1012 hertz and that has a radiant was a suggested compromise between standard format for the definitions of all intensity in that direction of 1/683 watt per proponents of a radiant-intensity formulation seven base units, that is, expressed in terms –1 3 steradian.” The value 1/683 W sr was chosen and those of a photon-intensity formulation . of its defining constant, Kcd. ❐ to maintain continuity with the previous The radiant-intensity side’s argument definitions based on candles and Planck is that the current definition serves well YUQIN ZONG is at the National Institute radiators. Indeed, an ordinary wax candle the practical needs of the classical world of of Standards and Technology, Gaithersburg, produces nearly 1 cd of luminous intensity. lighting and the majority of practitioners Maryland 20899, USA. The 1979 definition is given for only one of photometry and radiometry3. Such a e-mail: [email protected] frequency of optical radiation. To determine viewpoint implies, however, that direct References the luminous intensity of a light source realization of the candela using current 1. SI Brochure: The International System of Units 8th edn (BIPM, 2006). emitting monochromatic radiation with photon-number-based techniques is difficult 2. CCPR Report of the 20th Meeting to the International another frequency or a broad spectrum of and has much larger uncertainties than Committee for Weights and Measures (CIPM) (BIPM, 2009); http://go.nature.com/OXwCDR frequencies, the International Commission the present method of using a cryogenic 3. Zwinkels, J. C. et al. Metrologia 47, R15–R32 (2010). on Illumination (CIE) has defined a set radiometer — an electrical-substitution 4. SI Brochure Appendix 2: Mise en Pratique for the Definition of of weighting functions — called spectral radiometer that is operated at an extremely the Candela and Associated Derived Units for Photometric and Radiometric Quantities in the International System of Units (SI) luminous efficiency functions — that low temperature (typically, a few kelvin). The (BIPM, 2015). describe the relative spectral sensitivity of photon-intensity camp argues that proactive 5. Fischer, J. & Ullrich, J. Nature Phys. 12, 4–7 (2016). 614 NATURE PHYSICS | VOL 12 | JUNE 2016 | www.nature.com/naturephysics ©2016 Mac millan Publishers Li mited. All ri ghts reserved. .
Recommended publications
  • Lecture 3: the Sensor
    4.430 Daylighting Human Eye ‘HDR the old fashioned way’ (Niemasz) Massachusetts Institute of Technology ChriChristoph RstophReeiinhartnhart Department of Architecture 4.4.430 The430The SeSensnsoror Building Technology Program Happy Valentine’s Day Sun Shining on a Praline Box on February 14th at 9.30 AM in Boston. 1 Happy Valentine’s Day Falsecolor luminance map Light and Human Vision 2 Human Eye Outside view of a human eye Ophtalmogram of a human retina Retina has three types of photoreceptors: Cones, Rods and Ganglion Cells Day and Night Vision Photopic (DaytimeVision): The cones of the eye are of three different types representing the three primary colors, red, green and blue (>3 cd/m2). Scotopic (Night Vision): The rods are repsonsible for night and peripheral vision (< 0.001 cd/m2). Mesopic (Dim Light Vision): occurs when the light levels are low but one can still see color (between 0.001 and 3 cd/m2). 3 VisibleRange Daylighting Hanbook (Reinhart) The human eye can see across twelve orders of magnitude. We can adapt to about 10 orders of magnitude at a time via the iris. Larger ranges take time and require ‘neural adaptation’. Transition Spaces Outside Atrium Circulation Area Final destination 4 Luminous Response Curve of the Human Eye What is daylight? Daylight is the visible part of the electromagnetic spectrum that lies between 380 and 780 nm. UV blue green yellow orange red IR 380 450 500 550 600 650 700 750 wave length (nm) 5 Photometric Quantities Characterize how a space is perceived. Illuminance Luminous Flux Luminance Luminous Intensity Luminous Intensity [Candela] ~ 1 candela Courtesy of Matthew Bowden at www.digitallyrefreshing.com.
    [Show full text]
  • A Learner's Guide to SI Units and Their Conversion
    A Learner's Guide to SI Units and their Conversion October 2004 Workbook for students Learner's Guide to SI Units and their Conversion their and Units SI to Guide Learner's Edexcel A London Qualifications is one of the leading examining and awarding bodies in the UK and throughout the world. It incorporates all the qualifications previously awarded under the Edexcel and BTEC brand. We provide a wide range of qualifications including general (academic), vocational, occupational and specific programmes for employers. Through a network of UK and overseas offices, our centres receive the support they need to help them deliver their education and training programmes to learners. For further information please call Customer Services on 0870 240 9800, or visit our website at www.edexcel.org.uk Authorised by Jim Dobson Prepared by Sarah Harrison All the material in this publication is copyright © London Qualifications Limited 2004 CONTENTS Introduction 1 What are units? 2 Operations with units 5 Submultiple and multiple units 9 Conversion of units 11 Conversion examples and exercises 13 Length 13 Area 14 Volume 15 Mass 16 Time 17 Temperature 18 Density 19 Force 20 Stress and pressure 21 Answers to exercises 23 Introduction One of the important areas where Science and Technology students need support is in the conversion of units. This booklet is designed to be useful for students in all Science, Technology and Engineering subjects. This booklet has been produced to: S introduce students to SI base and derived units and S help students with the conversion of multiple and sub-multiple units to SI base and derived units.
    [Show full text]
  • Light and Illumination
    ChapterChapter 3333 -- LightLight andand IlluminationIllumination AAA PowerPointPowerPointPowerPoint PresentationPresentationPresentation bybyby PaulPaulPaul E.E.E. Tippens,Tippens,Tippens, ProfessorProfessorProfessor ofofof PhysicsPhysicsPhysics SouthernSouthernSouthern PolytechnicPolytechnicPolytechnic StateStateState UniversityUniversityUniversity © 2007 Objectives:Objectives: AfterAfter completingcompleting thisthis module,module, youyou shouldshould bebe ableable to:to: •• DefineDefine lightlight,, discussdiscuss itsits properties,properties, andand givegive thethe rangerange ofof wavelengthswavelengths forfor visiblevisible spectrum.spectrum. •• ApplyApply thethe relationshiprelationship betweenbetween frequenciesfrequencies andand wavelengthswavelengths forfor opticaloptical waves.waves. •• DefineDefine andand applyapply thethe conceptsconcepts ofof luminousluminous fluxflux,, luminousluminous intensityintensity,, andand illuminationillumination.. •• SolveSolve problemsproblems similarsimilar toto thosethose presentedpresented inin thisthis module.module. AA BeginningBeginning DefinitionDefinition AllAll objectsobjects areare emittingemitting andand absorbingabsorbing EMEM radiaradia-- tiontion.. ConsiderConsider aa pokerpoker placedplaced inin aa fire.fire. AsAs heatingheating occurs,occurs, thethe 1 emittedemitted EMEM waveswaves havehave 2 higherhigher energyenergy andand 3 eventuallyeventually becomebecome visible.visible. 4 FirstFirst redred .. .. .. thenthen white.white. LightLightLight maymaymay bebebe defineddefineddefined
    [Show full text]
  • Determination of Resistances for Brightness Compensation
    www.osram-os.com Application Note No. AN041 Determination of resistances for brightness compensation Application Note Valid for: TOPLED® / Chip LED® / Multi Chip LED® TOPLED E1608® /Mini TOPLED® / PointLED® Advanced Power TOPLED® / FIREFLY® SIDELED® Abstract This application note describes the procedure for adjusting the brightness of light emitting diodes (LEDs) in applications by means of resistors. For better repeatability, the calculation of the required resistance values is shown by means of an example. Author: Hofman Markus / Haefner Norbert 2021-08-10 | Document No.: AN041 1 / 14 www.osram-os.com Table of contents A. Introduction ............................................................................................................ 2 B. Basic procedure ..................................................................................................... 2 C. Possible sources of errors ..................................................................................... 3 Temperature ...................................................................................................... 3 Forward voltage ................................................................................................. 4 D. Application example .............................................................................................. 4 E. Conclusion ........................................................................................................... 12 A. Introduction Due to manufacturing tolerances during production, LEDs cannot be produced
    [Show full text]
  • 2.1 Definition of the SI
    CCPR/16-53 Modifications to the Draft of the ninth SI Brochure dated 16 September 2016 recommended by the CCPR to the CCU via the CCPR president Takashi Usuda, Wednesday 14 December 2016. The text in black is a selection of paragraphs from the brochure with the section title for indication. The sentences to be modified appear in red. 2.1 Definition of the SI Like for any value of a quantity, the value of a fundamental constant can be expressed as the product of a number and a unit as Q = {Q} [Q]. The definitions below specify the exact numerical value of each constant when its value is expressed in the corresponding SI unit. By fixing the exact numerical value the unit becomes defined, since the product of the numerical value {Q} and the unit [Q] has to equal the value Q of the constant, which is postulated to be invariant. The seven constants are chosen in such a way that any unit of the SI can be written either through a defining constant itself or through products or ratios of defining constants. The International System of Units, the SI, is the system of units in which the unperturbed ground state hyperfine splitting frequency of the caesium 133 atom Cs is 9 192 631 770 Hz, the speed of light in vacuum c is 299 792 458 m/s, the Planck constant h is 6.626 070 040 ×1034 J s, the elementary charge e is 1.602 176 620 8 ×1019 C, the Boltzmann constant k is 1.380 648 52 ×1023 J/K, 23 -1 the Avogadro constant NA is 6.022 140 857 ×10 mol , 12 the luminous efficacy of monochromatic radiation of frequency 540 ×10 hertz Kcd is 683 lm/W.
    [Show full text]
  • Guide for the Use of the International System of Units (SI)
    Guide for the Use of the International System of Units (SI) m kg s cd SI mol K A NIST Special Publication 811 2008 Edition Ambler Thompson and Barry N. Taylor NIST Special Publication 811 2008 Edition Guide for the Use of the International System of Units (SI) Ambler Thompson Technology Services and Barry N. Taylor Physics Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899 (Supersedes NIST Special Publication 811, 1995 Edition, April 1995) March 2008 U.S. Department of Commerce Carlos M. Gutierrez, Secretary National Institute of Standards and Technology James M. Turner, Acting Director National Institute of Standards and Technology Special Publication 811, 2008 Edition (Supersedes NIST Special Publication 811, April 1995 Edition) Natl. Inst. Stand. Technol. Spec. Publ. 811, 2008 Ed., 85 pages (March 2008; 2nd printing November 2008) CODEN: NSPUE3 Note on 2nd printing: This 2nd printing dated November 2008 of NIST SP811 corrects a number of minor typographical errors present in the 1st printing dated March 2008. Guide for the Use of the International System of Units (SI) Preface The International System of Units, universally abbreviated SI (from the French Le Système International d’Unités), is the modern metric system of measurement. Long the dominant measurement system used in science, the SI is becoming the dominant measurement system used in international commerce. The Omnibus Trade and Competitiveness Act of August 1988 [Public Law (PL) 100-418] changed the name of the National Bureau of Standards (NBS) to the National Institute of Standards and Technology (NIST) and gave to NIST the added task of helping U.S.
    [Show full text]
  • 2019 Redefinition of SI Base Units
    2019 redefinition of SI base units A redefinition of SI base units is scheduled to come into force on 20 May 2019.[1][2] The kilogram, ampere, kelvin, and mole will then be defined by setting exact numerical values for the Planck constant (h), the elementary electric charge (e), the Boltzmann constant (k), and the Avogadro constant (NA), respectively. The metre and candela are already defined by physical constants, subject to correction to their present definitions. The new definitions aim to improve the SI without changing the size of any units, thus ensuring continuity with existing measurements.[3][4] In November 2018, the 26th General Conference on Weights and Measures (CGPM) unanimously approved these changes,[5][6] which the International Committee for Weights and Measures (CIPM) had proposed earlier that year.[7]:23 The previous major change of the metric system was in 1960 when the International System of Units (SI) was formally published. The SI is a coherent system structured around seven base units whose definitions are unconstrained by that of any other unit and another twenty-two named units derived from these base units. The metre was redefined in terms of the wavelength of a spectral line of a The SI system after the 2019 redefinition: krypton-86 radiation,[Note 1] making it derivable from universal natural Dependence of base unit definitions onphysical constants with fixed numerical values and on other phenomena, but the kilogram remained defined in terms of a physical prototype, base units. leaving it the only artefact upon which the SI unit definitions depend. The metric system was originally conceived as a system of measurement that was derivable from unchanging phenomena,[8] but practical limitations necessitated the use of artefacts (the prototype metre and prototype kilogram) when the metric system was first introduced in France in 1799.
    [Show full text]
  • Indoor Selectable- Output Horns, Strobes, and Horn Strobes for Wall Applications
    Indoor Selectable- Output Horns, Strobes, and Horn Strobes for Wall Applications SpectrAlert® Advance audible visible notification products are rich with features guaranteed to cut installation times and maximize profits. Features The SpectrAlert Advance series offers the most versatile and easy-to-use line of horns, strobes, and horn strobes in the industry. • Plug-in design with minimal intrusion into the back box With white and red plastic housings, wall and ceiling mounting • Tamper-resistant construction options, and plain and FIRE-printed devices, SpectrAlert Advance • Automatic selection of 12- or 24-volt operation at can meet virtually any application requirement. 15 and 15/75 candela Like the entire SpectrAlert Advance product line, wall-mount horns, • Field-selectable candela settings on wall units: 15, 15/75, strobes, and horn strobes include a variety of features that increase 30, 75, 95, 110, 115, 135, 150, 177, and 185 their application versatility while simplifying installation. All devices • Horn rated at 88+ dBA at 16 volts feature plug-in designs with minimal intrusion into the back box, • Rotary switch for horn tone and three volume selections making installations fast and foolproof while virtually eliminating costly and time-consuming ground faults. • Universal mounting plate for wall units • Mounting plate shorting spring checks wiring continuity before To further simplify installation and protect devices from construction device installation damage, SpectrAlert Advance utilizes a universal mounting plate • Electrically Compatible with legacy SpectrAlert devices with an onboard shorting spring, so installers can test wiring continuity before the device is installed. • Compatible with MDL3 sync module • Listed for ceiling or wall mounting Installers can also easily adapt devices to a suit a wide range of application requirements using field-selectable candela settings, automatic selection of 12- or 24-volt operation, and a rotary switch for horn tones with three volume selections.
    [Show full text]
  • Illumination
    Illumination As a body is gradually heated above room temperature, it begins to radiate energy in the surrounding medium in the form of electromagnetic waves of various wavelengths. The nature of this radiant energy depends on the temperature of the hot body. The usual method of producing artificial light consists in raising a solid body or vapour to incandescence by applying heat to it. It is found that as body is gradually heated above room temperature, it begins to radiate energy in the surrounding medium in the form of electromagnetic waves of various wavelengths. The nature of this radiant energy depends on the temperature of the hot body. Thus, when the temperature is low, the radiated energy is in the form of heat waves only, but when a certain temperature is reached, light waves are also radiated out in addition to heat waves and the body becomes luminous. Further increase in the temperature produces an increase in the amount of both kinds of radiations but the colour of light or visual radiations change from bright red to orange, to yellow and finally, if the temperature is high enough, to white. As the temperature is increased, the wavelength of visible radiation goes on becoming shorter. It should be noted that heat waves are identical to light waves except that they are of longer wavelength and hence produce no impression on retina. Obviously, from the point of view of light emission, heat energy represents wasted energy. Radiant efficiency of the luminous source is defined as the ratio of “energy radiated in the form of light” to “total energy radiated out of the hot body” and it depends on the temperature of the source.
    [Show full text]
  • Worksheet 2 the Metric System and SI Units
    Unit Conversions Worksheet 2 The Metric System and SI Units 1 © MathTutorDVD.com Here is a helpful list of all the prefixes and their exponents and abbreviations: 109 giga G one billion 106 mega M one million 103 kilo k one thousand 102 hecto h one hundred 101 deca da ten 10-1 deci d one tenth 10-2 centi c one hundredth 10-3 milli m one thousandth 10-6 micro µ one millionth 10-9 nano n one billionth 10-12 pico p one trillionth 2 © MathTutorDVD.com 1. Give the abbreviation for each of the SI base units below. a. kilogram b. Kelvin c. meter d. second 2. State what quantities the following SI units are used to measure. a. kg b. m c. s d. K 3. Give the power of 10 that each of the following prefixes represents. a. kilo b. micro c. centi d. deca e. mega 3 © MathTutorDVD.com 4. Write the following numbers in their base units. a. 5 kilometers b. 12 centimeters c. 2 micrograms d. 4.1 megagrams 5. Write the abbreviations for the following measurements. a. 67 micrograms b. 831 kilometers c. 1.2 meters d. 791 megagrams 4 © MathTutorDVD.com 6. Express the following numbers with an appropriate SI prefix (e.g., 5,000 g = 5 kg). a. 7800 m b. 5.0 x 10-6 g c. 7.8 x 106 m d. 1.6 x 10-3 g 7. Convert the following to scientific notation using the base SI unit. a. 4.51 microseconds b. 6700 grams c.
    [Show full text]
  • The International System of Units (SI)
    NAT'L INST. OF STAND & TECH NIST National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce NIST Special Publication 330 2001 Edition The International System of Units (SI) 4. Barry N. Taylor, Editor r A o o L57 330 2oOI rhe National Institute of Standards and Technology was established in 1988 by Congress to "assist industry in the development of technology . needed to improve product quality, to modernize manufacturing processes, to ensure product reliability . and to facilitate rapid commercialization ... of products based on new scientific discoveries." NIST, originally founded as the National Bureau of Standards in 1901, works to strengthen U.S. industry's competitiveness; advance science and engineering; and improve public health, safety, and the environment. One of the agency's basic functions is to develop, maintain, and retain custody of the national standards of measurement, and provide the means and methods for comparing standards used in science, engineering, manufacturing, commerce, industry, and education with the standards adopted or recognized by the Federal Government. As an agency of the U.S. Commerce Department's Technology Administration, NIST conducts basic and applied research in the physical sciences and engineering, and develops measurement techniques, test methods, standards, and related services. The Institute does generic and precompetitive work on new and advanced technologies. NIST's research facilities are located at Gaithersburg, MD 20899, and at Boulder, CO 80303.
    [Show full text]
  • Measuring Luminance with a Digital Camera
    ® Advanced Test Equipment Rentals Established 1981 www.atecorp.com 800-404-ATEC (2832) Measuring Luminance with a Digital Camera Peter D. Hiscocks, P.Eng Syscomp Electronic Design Limited [email protected] www.syscompdesign.com September 16, 2011 Contents 1 Introduction 2 2 Luminance Standard 3 3 Camera Calibration 6 4 Example Measurement: LED Array 9 5 Appendices 11 3.1 LightMeasurementSymbolsandUnits. 11 3.2 TypicalValuesofLuminance.................................... 11 3.3 AccuracyofPhotometricMeasurements . 11 3.4 PerceptionofBrightnessbytheHumanVisionSystem . 12 3.5 ComparingIlluminanceMeters. 13 3.6 FrostedIncandescentLampCalibration . 14 3.7 LuminanceCalibrationusingMoon,SunorDaylight . 17 3.8 ISOSpeedRating.......................................... 17 3.9 WorkFlowSummary ........................................ 18 3.10 ProcessingScripts.......................................... 18 3.11 UsingImageJToDeterminePixelValue . 18 3.12 UsingImageJToGenerateaLuminance-EncodedImage . 19 3.13 EXIFData.............................................. 19 References 22 1 Introduction There is growing awareness of the problem of light pollution, and with that an increasing need to be able to measure the levels and distribution of light. This paper shows how such measurements may be made with a digital camera. Light measurements are generally of two types: illuminance and lumi- nance. Illuminance is a measure of the light falling on a surface, measured in lux. Illuminanceis widely used by lighting designers to specify light levels. In the assessment of light pollution, horizontal and vertical measurements of illuminance are used to assess light trespass and over lighting. Luminance is the measure of light radiating from a source, measured in candela per square meter. Luminance is perceived by the human viewer as the brightness of a light source. In the assessment of light pollution, (a) Lux meter luminance can be used to assess glare, up-light and spill-light1.
    [Show full text]