BRITISH STANDARD AUTOMOBILE SERIES CONFIRMED DECEMBER 1987 BS AU 170 1979 Methods for Measurement of reflectance of rear view mirrors UDC 629 113 0181 535 346 1 BS AU 170 1979 This British Standard, h[.]
BRITISH STANDARD AUTOMOBILE SERIES C O NFI RME D D E C E MBE R 987 Methods for Measurement of reflectance of rear view mirrors UD C 62 1 81 : 5 46 BS AU 170:1979 BS AU 70 : 979 Fore word This British Standard, which has been prepared under the direction of the Road vehicles — Rearview mirrors — Test method for determining reflectivity” Automobile Standards Committee, is based on ISO 5740 “ A British Standard does not purport to include all the necessary provisions of a contract Users of British Standards are responsible for their correct application C o mp liance with a British S tand ard doe s not o f itse lf co nfe r immunity fro m le gal ob ligations S ummary o f p age s This document comprises a front cover, an inside front cover, pages i and ii, pages to and a back cover This standard has been updated (see copyright date) and may have had amendments incorporated This will be indicated in the amendment table on This British Standard, having the inside front cover been prepared under the direction of the Automobile Standards Committee, was published under the authority of the Executive Board on Ame ndme nts issue d since p ub lication 28 February 979 © BSI 03- 2000 The following BSI references relate to the work on this standard: Committee reference AUE/Draft for comment 77/73276 DC IS B N 80 Amd No Date of issue Comments BS AU 170:1979 Contents Page Foreword Inside front cover Scope and field of application References D efinitions Apparatus Procedures Appendix A Spectral tristimulus values for C IE 931 standard colorimetric observer Figure — Generalized reflectometer showing geometries for © BSI 03- 000 the two calibration methods Figure — Generalized reflectometer incorporating an integrating sphere i ii blank BS AU : 97 S cop e and fie ld of ap p lication NOTE In the CIE 931 standard colorimetric system, applicable to observing fields of angular subtense This British Standard specifies a test method for between ° and ° (0 01 and 07 rad) , these tristimulus determining the reflectance of rear- view mirrors for values road vehicles x ( Ỉ) , y ( Ỉ) , z ( Ỉ) are so chosen that the values of are identical with the spectral luminous efficiencies V y (2) ( Ỉ) (See Appendix A ) It applies to flat and convex surface mirrors 3.5 intended for internal and external mounting p hotop ic vision (as defined in term number 402 1 1 of BS 4727- 4: Group 02: 971 ) Re fe re nce s vision by the normal eye when it is adapted to levels The following publications are referred to in this of luminance of at least several candelas per square standard metre BS 354, Reco m m endatio ns for p ho to m etric BS 667, NOTE The cone receptors of the retina are considered to be the principal active elements under these conditions and the integrators spectrum appears coloured Po rtab le p hotoelectric p hotom eters re fle ctance BS 4727, Glo ssary o f electrotechnical, p ow er, teleco m m unications, electro nics, lighting and colour term s — Part 4: Term s p articular to lighting and colour — Gro up 01 : Radiation and p hotom etry — Gro up 02: Vision and colour term inology the ratio of reflected luminous flux to the incident luminous flux (Ô) NOTE Where mixed reflection occurs, the total reflectance may be divided into two parts, specular reflectance (Ô r) and diffuse reflectance (Ô d) Total reflectance may be expressed by the D e finitions following equation: For the purposes of this British Standard, the following definitions apply Ô=Ô r + Ô d App aratus 3.1 C IE standard illuminant A (as defined in term number 402 2031 of BS 4727- 4: Group 02: 971 ) colorimetric illuminant, representing the full radiator at T 68 (as defined in term number 401 3008 of BS 4727- 4: Group 01 : 971 ) = 855 K General The apparatus shall consist of a light source, a holder for the test sample, a reflectometer with a photodetector and an indicating meter (see Figure ) , and a means of eliminating the effects of extraneous light 3.2 The reflectometer in Figure measures the specular C IE standard source A (as defined in term number 402 2032 of BS 4727- 4: Group 02: 971 ) gas- filled tungsten filament lamp operating at a correlated colour temperature of T 68 = 855 K component of reflectance The reflectometer may incorporate a light- integrating sphere to facilitate measuring the reflectance of non- flat (convex) mirrors 3.3 (see Figure 2) In this case the reflectometer C IE stand ard co lo rime tric ob se rve r measures the total reflectance, i e the sum of the (as defined in term number 402 201 of BS 4727- 4: Group 02: 971 ) The required characteristics of the components of receptor of radiation whose colorimetric characteristics correspond to the spectral tristimulus values x ( Æ) , y specular and diffuse components ( Æ) , z ( Ỉ ) adopted by the the apparatus are described in BS 354 and in BS 667 Sp ectral characteristics of light source and International Commission on Illumination in 931 reflecto m eter (See standard source A and associated optics to provide a 3.4 and Appendix A ) The light source shall consist of a CIE near- collimated light beam A voltage stabilizer is 3.4 C IE sp e ctral tristimulus value s (as defined in term number 402 2008 of BS 4727- 4: recommended to maintain a fixed lamp voltage during instrument operation Group 02: 971 ) tristimulus values of the spectral components of an equienergy spectrum in the CIE (XYZ) system NOTE Formerly CIE- distribution coefficients © BSI 03- 2000 BS AU 70:1 979 The reflectometer shall have a photodetector with a spectral response proportional to the photopic luminosity function of the CIE (1931) standard colorimetric observer (See Appendix A.) Any other combination of illuminant-filter-receptor giving the overall equivalent of CIE standard illuminant A and photopic vision may be used When an integrating sphere is used in the reflectometer, the interior surface of the sphere shall be coated with a matt (diffusive) spectrally non-selective white coating 4.3 The angle of the incident beam (Úi) should preferably be 0.44 ± 0.09 rad (25 ± °) from the perpendicular to the test surface and shall not exceed the upper limit of the tolerance (i.e 0.53 rad or 30°) The axis of the receptor shall make an angle (Úr) with this perpendicular equal to that of the incident beam (see Figure 1) The incident beam upon arrival at the test surface shall have a diameter of not less than 19 mm (0.75 in) The reflected beam shall be narrower than the sensitive area of the photodetector, shall cover not less than 50 % of such area, and as nearly as possible shall cover the same area segment as used during instrument calibration Geometric conditions NOTE If the beam width is the same as the sensitive area, problems with vignetting may occur Procedures 5.1 General Four procedures, for use with different kinds of measuring instruments, are given below (See 5.2 to 5.6 ) 5.2 Direct calibration method In the direct calibration method, the incident flux is used as the reference standard This method is applicable to those instruments which are so constructed as to permit calibration at the 100 % point by swinging the receiver to a position directly on the axis of the light source (see Figure 1) It may be desirable in some cases (such as when measuring low-reflectance surfaces) to use an intermediate calibration point (between and 100 % on the scale) with this method In these cases, a neutral density filter of known transmittance shall be inserted in the optical path, and the calibration control can then be adjusted until the meter reads the percentage transmission of the neutral density filter This filter shall be removed before making measurements on the sample NOTE To expand the scale when dealing with low-reflectance samples, it may be desirable to set a full-scale reading with the calibrated filter and multiply the apparent measured reflectance by the transmittance of the filter The indirect calibration method is applicable to those instruments with fixed source and receiver geometry A properly calibrated and maintained reflectance standard is required This reference standard should preferably be a flat mirror with a reflectance value as near as possible to that of the test samples 5.4 Flat mirror measurement The reflectance of flat mirror samples can be measured on instruments employing either the direct or indirect 4.4 calibration method The reflectance value is read The photodetector directly from the indicating meter output as read on the indicating meter shall be a 5.5 Non-flat (convex) mirror measurement The linear function of the light intensity on the measurement of the reflectance of non-flat (convex) photo-sensitive area Means (electrical and/or mirrors require requires the use of instruments optical) shall be provided to facilitate zeroing and which incorporate an integrating sphere calibration adjustments Such means shall not (see Figure 2) If the indicating meter affect the linearity or the spectral characteristics of indicates divisionsinstrument with a reference standard the instrument The accuracy of the mirror of % reflectance, then, with a mirror of receptor-indicator unit shall be within ± % of full unknown reflectance, divisions will correspond to scale, or ± 10 % of the magnitude of the reading, a reflectance of %, given by the formula whichever is the smaller 4.5 The mechanism shall be capable of locating the test sample so that the axes of the where the symbols are as given above source arm and receptor arm intersect at the principle reflecting surface The reflecting surface may lie within or at either face of the mirror sample, depending on whether it is a first-surface, second-surface, or prismatic “flip” type mirror When an integrating sphere is used in the reflectometer, the sphere shall have a minimum diameter of 127 mm (5 in) The sample and incident beam apertures in the sphere wall shall be of such a size as to admit the entire incident and reflected light beams The photodetector shall be located so as not to receive direct light from either the incident or the reflected beams, and should be screened from any scattered light which might pass directly from the sample (see Figure 2) 5.3 Indirect calibration method Electrical characteristics of the photodetector-indicator unit nE E nX X Sample holder © BSI 03-2000 BS AU : 97 Me asure me nt o f diffuse co mp o ne nt o f The glos s trap may cons is t of a b lackened cap re fle ctance The reflectometer shown in Figure covering an additional p ort hole, or a b lackened may als o b e used to meas ure the diffuse comp onents of reflectance sep arately In this case a gloss trap s hall b e us ed which covers the geometrical op tical cross s ection of the regularly reflected b eam from the s amp le, allowing for any curvature of the cavity held b ehind this additional p ort hole When this additional p ort hole exis ts in the reflectometer, it should b e covered b y a whitened cap whos e coating is as similar to the s p here walls and coating as p oss ib le s amp le © BS I - 00 BS AU 170:1979 Appendix A Spectral tristimulus values for the CIE 1931 standard colorimetric observer NOTE This table, which is extracted from IEC Publication 50(45) (1 970) , has been abridged The values of ( ) = V2 ( ) are rounded to four decimal places x ( Ỉ) y ( Ỉ) z ( Æ) mm 380 001 000 0 006 390 004 000 020 400 01 000 067 41 0 043 001 207 420 34 004 0 645 430 283 01 385 440 348 023 747 450 336 038 772 460 290 060 669 470 95 091 287 480 095 39 0 81 490 032 0 208 0 465 500 004 323 0 272 51 0 009 503 0 58 520 063 71 0 078 530 65 862 0 042 540 290 954 0 020 550 433 995 0 008 560 594 995 0 003 570 762 952 0 002 580 91 870 0 001 590 026 757 0 001 600 062 631 0 000 61 002 503 0 000 620 854 381 0 000 630 642 265 0 000 640 447 75 0 000 650 283 07 0 000 660 64 061 0 000 670 087 032 0 000 680 046 01 0 000 690 022 008 000 700 01 004 000 71 0 005 002 000 720 002 001 0 000 730 001 000 740 000 000 750 000 000 000 760 000 000 000 770 000 000 0 000 780 000 0 000 0 000 a 000 a 000 In 966 this value was altered from 0003 to 0002 © BSI 03- 2000 BS AU 170:1979 Figure — Generalized reflectometer showing geometries for the two calibration methods © BSI 03- 000 BS AU 170:1979 Figure — Generalized reflectometer incorporating an integrating sphere © BSI 03 - 000 blank BS AU 170:1979 BSI — British Standards Institution BS I is the indep endent national b ody res p ons ib le for p rep aring Britis h S tandards It p res ents the UK view on s tandards in E urop e and at the international level It is incorp orated b y Royal C harter Revisions Britis h S tandards are up dated b y amendment or revis ion Us ers 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