BS-ISO-23539-2005.pdf

BRITISH STANDARD BS ISO 23539:2005 Photometry The CIE system of physical photometry ICS 17.180.01 ? Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 04:34:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 23539:2005 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 23 January 2006 © BSI 23 January 2006 ISBN 0 580 46881 X National foreword This British Standard reproduces verbatim ISO 23539:2005 and implements it as the UK national standard. The UK participation in its preparation was entrusted by Technical Committee CPL/34, Lamps and related equipment, to Subcommittee CPL/34/5, Photometry and light classifications, which has the responsibility to: A list of organizations represented on this subcommittee can be obtained on request to its secretary. Cross-references The British Standards which implement international publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the ISO title page, pages ii and iii, a blank page, pages 1 to 18, an inside back cover and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. DateComments Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 04:34:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI Reference number ISO 23539:2005(E) CIE S 010/E:2004 INTERNATIONAL STANDARD ISO 23539 CIE S 010/E First edition 2005-08-01 Photometry The CIE system of physical photometry Photométrie Le système CIE de photométrie physique BS ISO 23539:2005 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 04:34:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 04:34:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI iii Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. ISO 23539 was prepared as Standard CIE S 010/E by the International Commission on Illumination, which has been recognized by the ISO Council as an international standardizing body. It was adopted by ISO under a special procedure which requires approval by at least 75 % of the member bodes casting a vote, and is published as a joint ISO/CIE edition. The International Commission on Illumination (abbreviated as CIE from its French title) is an organization devoted to international cooperation and exchange of information among its member countries on all matters relating to the science and art of lighting. ISO 23539 was prepared by CIE Technical Committee 2-35 CIE Standard for V() and V(). BS ISO 23539:2005 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 04:34:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI blank Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 04:34:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 1 PHOTOMETRY - THE CIE SYSTEM OF PHYSICAL PHOTOMETRY INTRODUCTION The visual brightness of a light source depends not only on the amount of radiation it emits but also on its spectral composition and on the visual response function of the observer viewing it. Because human visual response varies at different light levels and from person to person, precise photometry requires the definition of representative standard observers. The CIE system of physical photometry specifies procedures for the quantitative evaluation of optical radiation in terms of the spectral luminous efficiency functions of two such standard observers. One, V(?), represents photopic vision and the other, V?(?), scotopic vision. Used in conjunction with the SI photometric base unit, the candela, these functions constitute a system that enables the values of photometric quantities for all types of luminous source to be precisely determined, regardless of the spectral composition of the radiation emitted. 1. SCOPE This international Standard specifies the characteristics of the system of physical photometry established by the CIE and accepted as the basis for the measurement of light. It defines the photometric quantities, units and standards that make up the CIE system of physical photometry and that have been officially accepted by the Comité International des Poids et Mesures (CIPM). They comprise: ?the definition of photometric quantities and units, ?the definition of CIE standard spectral luminous efficiency functions for photopic and scotopic vision, ?the definition of a CIE standard photometric observer that conforms to these functions, ?the definition of maximum luminous efficacies for photopic and scotopic vision. An informative annex provides a vocabulary of related terms. 2. PHOTOMETRIC QUANTITIES Photometric quantities are defined in the International Lighting Vocabulary (ILV) (CIE, 1987a). 2.1 Luminous flux The fundamental physical quantity used in optical radiometry is the radiant flux or radiant power,?e, measured in watts, which is emitted by a source of radiation, transmitted by a medium of propagation, or received at a surface. The corresponding photometric quantity is: luminous flux (? ?v) (see ILV 845-01-25) quantity derived from radiant flux ?e by evaluating the radiation according to its action upon the CIE standard photometric observer The procedure for deriving ?v? from ?e? is defined in 4.3, below. 2.2 Other quantities The following are the photometric quantities that correspond to the most important radiometric quantities defined in the International Lighting Vocabulary. luminous energy (also known as quantity of light) (Qv) (see ILV 845-01-28) time integral of the luminous flux ?v over a given duration ?t ? ? ? t tQd vv ? luminous intensity (of a source in a given direction) (Iv) (see ILV 845-01-31) quotient of the luminous flux d?v leaving the source and propagated in the element of solid angle d? containing the given direction, by the element of solid angle BS ISO 23539:2005 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 04:34:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 2 ?d d v v ? ?I? luminance (in a given direction, at a given point of a real or imaginary surface) (Lv) (see ILV 845-01-35) quantity defined by the formula ?A L dcosd d v v ? ? ? ? where d?v is the luminous flux transmitted by an elementary beam passing through the given point and propagating in the solid angle d? containing the given direction; dA is the area of a section of that beam containing the given point; ? is the angle between the normal to that section and the direction of the beam illuminance (at a point of a surface) (Ev) (see ILV 845-01-38) quotient of the luminous flux d?vincident on an element of the surface containing the point, by the area dA of that element A E d d v v ? ? luminous exitance (at a point of a surface) (Mv) (see ILV 845-01-48) quotient of the luminous flux d?v leaving an element of the surface containing the point, by the area dA of that element A M d d v v ? ? 3. PHOTOMETRIC UNITS 3.1 Candela The SI photometric base unit is the candela (cd), the unit of luminous intensity. It was defined by the Conférence Générale des Poids et Mesures (CGPM) in 1979 (CGPM, 1979), as follows: The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 10 12 hertz and that has a radiant intensity in that direction of (1/683) watt per steradian. This definition of the candela applies equally to photopic, scotopic, and mesopic vision. 3.2 Other units The SI units of other photometric quantities can be derived from the candela and the SI units of length (m), solid angle (sr) and time (s). Thus: QuantitySymbolSI Unit Luminous flux ?vlm = cd·sr Luminous energy Qvcd·sr·s LuminanceLvcd·m-2 IlluminanceEvlx = cd·sr·m-2 Luminous exitance Mvcd·sr·m-2 BS ISO 23539:2005 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 04:34:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 3 4. PHOTOMETRIC STANDARDS 4.1 CIE Standard spectral luminous efficiency functions for photopic and scotopic vision This Standard defines two spectralluminous efficiency functions for photometric measurements: - The V(?) function, which applies to photopic vision and should be used for measurements at luminance levels of at least several candelas per square metre. It is defined by the numerical values given in Table 1 of this Standard, the wavelength being measured in standard air (Birch, 1994). For numerical computations, the peak value of the V(?) function should be evaluated at 555 nm exactly. Linear interpolation should be used exclusively to evaluate V(?) at wavelengths intermediate to those given in Table 1; - The V?(?) function, which applies to scotopic vision and should be used for measurements at luminance levels less than some hundredths of a candela per square metre. This function is defined by the numerical values in Table 2 of this Standard, the wavelength? again being measured in standard air. For numerical computations, the peak value of the V?(?) function should be evaluated at 507 nm exactly. Linear interpolation should be used exclusively to evaluate V?(?) at wavelengths intermediate to those given in Table 2. An ideal observer having a relative spectral responsivity curve that conforms to the V(?) function for photopic vision or the V?(?) function for scotopic vision, and that complies with the summation law implied in the definition of luminous flux, is known as a CIE standard photometric observer. The CIE has not, so far, defined standard spectral luminous efficiency functions for the mesopic region, intermediate between the ranges of photopic and scotopic vision. 4.2 Maximum luminous efficacies for photopic and scotopic vision The V(?) and V?(?) functions defined in this Standard supplement the 1979 candela definition in a manner that, taken together, these definitions constitute a rational system of physical photometry which ?correlates the radiant power of broadband radiation acting upon the human visual system with the physiological characteristics of the latter, ?is consistent with visual experience for photopic and scotopic vision, ?establishes precisely defined numerical relationships between radiometric and photometric quantities. Based on the following definitions and considerations, these numerical relationships are defined by equations (1) to (4), below. luminous efficacy (for monochromatic radiation of wavelength ?) K(? ?) and K?(? ?) Quotient of the luminous flux ?v by the corresponding radiant flux ?e ? ? ?(for photopic vision) (1) 1 e v m Wlm ? ? ? ? ?VKK ? ? ? 1 e v m Wlm ' ''' ? ? ? ? ?VKK?(for scotopic vision) (2) where the maximum values of K(?) and K?(?) are denoted by Km and K?m so that Km= K(555 nm) and K?m = K?(507 nm). The frequency 540 x 1012 Hz corresponds to a wavelength of 555,016 nm in standard air and it follows from the candela definition that K(555,016 nm) = K?(555,016 nm) = 683 lm·W-1. Therefore, according to equations 1 and 2, Km = 683 lm·W-1 / V(555,016 nm) = 683,002 lm·W-1 (3) K?m = 683 lm·W-1 / V?(555,016 nm) = 1700,05 lm·W-1 (4) For all practical photometric applications, Km can be taken as equal to 683 lm·W-1 and K?m as equal to 1700 lm·W-1. BS ISO 23539:2005 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 04:34:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 4 4.3 Fundamental equations relating photometric and radiometric quantities The method for implementing the definition of luminous flux given in 2.1 is based on equations (1) to (4), above. If the luminous flux in question pertains to photopic vision, it is related to the corresponding spectral concentration of radiant flux by the equation ? ? ? d 0 e,mv VK? ? ? (5) and the corresponding relation for scotopic vision is ? ? ? d 0 e,mv V'K''? ? ? (6) In these equations Km and K?m are defined by equations (3) and (4) above and V(?) and V?(?) are defined by Tables 1 and 2 of this Standard. Equations (5) and (6) are fundamental to the CIE system of physical photometry. 4.4 Measurement procedures In practice, the spectral weighting required by equations (5) and (6) can be realized by means of absolutely calibrated, V(?) or V?(?) corrected detectors that conform to the definition of the CIE standard photometric observer. In such cases, the integrations specified are performed by the detector itself. The evaluation of photometers designed to measure light is dealt with in the Publication CIE 69 1987, Methods of Characterizing Illuminance Meters and Luminance Meters (CIE, 1987b). Alternatively, it is possible to make spectroradiometric measurements (CIE, 1984) and obtain the required integrals by numerical computation from the spectroradiometric data. In this case, the integrations usually take the form of numerical summations over the visible spectrum. The tabulated values of V(?) and V?(?) at 1 nm intervals are normally sufficient for this purpose, but if intermediate values are required, these should be obtained from the tabulated values by linear interpolation. In this Standard, values are given for the photopic standard observer V(?) over the spectral range from 360 nm to 830 nm (Table 1) and for the scotopic standard observer V?(?) over the spectral range from 380 nm to 780 nm (Table 2). The CIE does not define values for the standard observers outside these spectral ranges, because, for all practical photometric purposes, the visual contribution at longer or shorter wavelength is negligible. Definitive values of the photometric quantities will be obtained if the summation is carried out at 1 nm intervals and the limits set to 360 nm and 830 nm in equation (5) and to 380 nm and 780 nm in equation (6). The above e