1、Designation: E 809 08Standard Practice forMeasuring Photometric Characteristics of Retroreflectors1This standard is issued under the fixed designation E 809; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision
2、 A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice describes the general procedures for in-strumental measurement of the photometric characteristics ofretroreflective
3、materials and retroreflective devices.1.2 This practice is a comprehensive guide to the photom-etry of retroreflectors but does not include geometric terms thatare described in Practice E 808.1.3 This practice describes the parameters that are requiredwhen stating photometric measurements in specifi
4、c tests andspecifications for retroreflectors.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility
5、of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 284 Terminology of AppearanceE 308 Practice for Computing the Colors of Objects byUsing the CIE Syst
6、emE 808 Practice for Describing Retroreflection2.2 CIE Documents:CIE Publication No. 54.2 RetroreflectionDefinition andMeasurement3CIE Publication No. 17.4 International Lighting Vocabu-lary3CIE Publication No. 69-1987 Methods of CharacterizingIlluminance Meters and Luminance Meters33. Terminology3.
7、1 Terms and definitions in Terminology E 284 and E 808are applicable to this practice. In general, the terminology inthis practice agrees with that in CIE Publications 17.4 and 54.2.3.2 Definitions of Terms Specific to This Standard:3.2.1 annular aperture, nthe difference between the an-gular diamet
8、ers of the external boundary circle and the internalboundary circle.3.2.2 circular aperture, nthe angular diameter of a circu-lar aperture surface.3.2.3 goniometer, nan instrument for measuring or settingangles.3.2.4 photopic receiver, na receiver of radiation with aspectral responsivity which confo
9、rms to the V (l) distributionof the CIE Photopic Standard Observer that is specified inPractice E 308.3.2.5 receiver aperture, nangular dimensions from theretroreflector center to the entrance aperture or pupil of thereceiver.3.2.6 rectangular aperture, nthe angular height and widthof a rectangular
10、aperture surface.3.2.6.1 DiscussionThe orientation of the sides of therectangular aperture surface should be supplied together withthe angular height and width.3.2.7 reflected illuminance, Er, nilluminance at the re-ceiver measured on a plane perpendicular to the observationaxis.3.2.7.1 DiscussionTh
11、is quantity is used in the calculationof the coefficient of luminous intensity,RI: RI=(I/E)=(Erd2)/E, where d is the distance from theretroreflector to the receptor.3.2.8 retroreflectometer aperture angles, nthe maximumangular diameter of the pencil of light (see Fig. 1).3.2.8.1 DiscussionIn practic
12、e the illumination arrives atthe retroreflector center within a narrow pencil of light sur-rounding the illumination axis and the light reflected to thephotoreceptor is contained within another narrow pencil. Thedistribution of light within such pencils is the “aperture”function and the maximum angu
13、lar diameter of the pencil is the1This practice is under the jurisdiction of ASTM Committee E12 on Color andAppearance and is the direct responsibility of Subcommittee E12.10 on Retrore-flection.Current edition approved Jan. 1, 2008. Published February 2008. Originallyapproved in 1981. Last previous
14、 edition approved in 2002 as E 809 02.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from U.S. Na
15、tional Committee of the CIE (International Commissionon Illumination), C/o Thomas M. Lemons, TLA-Lighting Consultants, Inc., 7 PondSt., Salem, MA 01970, http:/www.cie-usnc.org1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.“aperture
16、angle.” It is generally assumed that the aperturefunctions are rotationally symmetrical and even uniform, butthis is often false, especially for illumination.3.2.9 retroreflector aperture surface, nthe aperture sur-face of a retroreflector is given by the retroreflector itself, or bya diaphragm encl
17、osing part of the retroreflector.3.2.10 retroreflector element aperture, nangular dimen-sion of the aperture surface of a retroreflective element as seenfrom the receivers center.3.2.10.1 DiscussionThe element aperture quantifies anerror source in the setting of the observation angle. This is acriti
18、cal feature for testing large retroreflective elements or atshort distances. When using collimated optics, placing thesource and receiver at virtual infinity, the retroreflector elementaperture is virtually zero.3.2.11 retroreflector (or specimen) aperture, nangulardimensions from the source point o
19、f reference to the aperturesurface of the retroreflector (or specimen).3.2.11.1 DiscussionAs the source and receiver are gener-ally close to each other, distinction is not made betweenaperture angles seen from the source and receiver. When usingcollimated optics where the source and receiver are at
20、virtualinfinity, the retroreflector aperture is virtually naught. Theretroreflector aperture describes the maximum variation of theentrance angle of the aperture surface of the retroreflector.3.2.12 source aperture, nangular dimensions from theretroreflector center to the exit aperture stop or pupil
21、 of thelight source.4. Summary of Practice4.1 The fundamental procedure described in this practiceinvolves measurements of retroreflection based on the ratio ofthe retroreflected illuminance at the observation position to theincident illuminance measured perpendicular to the illumina-tion axis at th
22、e retroreflector. From these measurements, alongwith the geometry of test, various photometric quantitiesapplicable to retroreflectors can be determined.4.2 Also described are methods of comparative testingwhere unknown specimens are measured relative to an agreed-upon standard retroreflector (a sub
23、stitution test method).5. Significance and Use5.1 This practice describes procedures used to measurephotometric quantities that relate to the visual perception ofretroreflected light. The most significant usage is in the relationto the nighttime vehicle headlamp, retroreflector, and driverseye geome
24、try. For this reason the CIE Standard Source A isused to represent a tungsten vehicle headlamp and the receptorhas the photopic, V (l), spectral responsivity corresponding tothe light adapted human eye. Although the geometry must bespecified by the user, it will, in general, correspond to therelatio
25、n between the vehicle headlamp, the retroreflector, andthe vehicle drivers eye position.6. Uses and Applications6.1 Coeffcient of RetroreflectionThis quantity is used tospecify the performance of retroreflective sheeting. It considersthe retroreflector as an apparent point source whose retrore-flect
26、ed luminous intensity is dependent on the area of theretroreflective surface involved. It is a useful engineeringquantity for determining the photometric performance of suchretroreflective surfaces as highway delineators or warningdevices. The coefficient of retroreflection may also be used todeterm
27、ine the minimum area of retroreflective sheeting neces-sary for a desired level of photometric performance.6.2 Coeffcient of Luminous IntensityThis term is used tospecify the performance of retroreflective devices. It considersthe retroreflected luminous intensity as a function of theperpendicular i
28、lluminance incident on the device. It is recom-mended for use in describing performance of RPMs, taillightreflex reflectors and roadway delineators.6.3 Coeffcient of Line Retroreflection (of a ReflectingStripe)This term may be used to describe the retroreflectiveperformance of long narrow strips of
29、retroreflective materials,when the actual width is not as important as is the reflectivityper unit length.6.4 Reflectance Factor (of a Plane Reflecting Surface)This is a useful term for comparing surfaces specificallydesigned for retroreflection to surfaces which are generallyconsidered to be diffus
30、e reflectors. Since almost all naturalsurfaces tend to retroreflect slightly, materials such as BaSO4can have a reflectance factor much higher than one (as much asfour) at small observation angles. Such diffuse reflectancestandards should be used for calibration only at large observa-tion angles, fo
31、r example, 45.6.5 Coeffcient of Retroreflected Luminance (also calledSpecific Luminance)This term considers the retroreflector asa surface source whose projected area is visible as an area atthe observation position. The coefficient of retroreflectedluminance relates to the way the effective retrore
32、flectivesurface is focused on the retina of the human eye and to thevisual effect thereby produced. It is recommended for describ-ing the performance of highway signs and striping or largevehicular markings which are commonly viewed as discerniblesurface areas.6.6 Coeffcient of Luminous Flux per Uni
33、t Solid Angle,RFThis measurement is used to evaluate retroreflectors onthe basis of flux ratios. It is numerically very nearly equal tothe coefficient of retroreflected luminance at small entranceangles. It is recommended for use in the design of retroreflec-tors but not for specification purposes.F
34、IG. 1 Illustration of Apertures used in RetroreflectionMeasurementE8090827. Requirements When Measuring Retroreflectors7.1 When describing photometric measurements of retrore-flectors, items in paragraphs 7.1.1-7.1.11 must be included.Refer to Fig. 2 for a diagram of measurement geometryterminology.
35、7.1.1 Retroreflective photometric quantity, such as: coeffi-cient of luminous intensity (RI), coefficient of retroreflectedluminance (RL) (also called specific luminance), coefficient ofretroreflection (RA), coefficient of line retroreflection (RM),reflectance factor (RF), or coefficient of luminous
36、 flux per unitsolid angle (RF).7.1.1.1 In specifications, a minimum acceptable quantitativevalue is usually established.7.1.2 Units in which each quantity is to be measured (forexample cdlx1m2).7.1.3 Observation angle.7.1.4 Components of the entrance angle, (b1and b2).7.1.4.1 When both b1and b2are n
37、ear zero, care must betaken to prevent specular reflection from entering the photore-ceptor.7.1.4.2 Entrance angle b equals cos1(cosb1cosb2).7.1.5 Rotation angle and the datum mark position shall bespecified if random rotational orientation of the test specimenis not suitable.7.1.6 Test distance or
38、minimum test distance.7.1.7 Test specimen size and shape.7.1.8 Photoreceptor angular aperture.7.1.9 Source angular aperture.7.1.10 Retroreflector center.7.1.11 Retroreflector axis. The retroreflector axis is usuallyperpendicular to the surface of retroreflective sheeting. In suchcomplex devices as a
39、utomobile or bicycle reflectors, theretroreflector axis and retroreflector center may be defined withrespect to the illumination direction.8. Apparatus8.1 GeneralThe apparatus shall consist of a photorecep-tor, a light projector source, a specimen goniometer, anobserver goniometer, (sometimes known
40、as the observationangle positioner), and a photometric range.8.1.1 Aperture angles are a very important considerationwhen measuring retroreflectors as Fig. 1 illustrates. See Table1 for recommendations for maximum angular aperture ofoptical elements. See 9.1 on selection of angular apertures.8.2 Pho
41、toreceptorThe photoreceptor shall be equipped asfollows:8.2.1 Photopic FilterThe photoreceptor shall be equippedwith a light filter such that the spectral responsivity of thereceptor should match the V (l) response of the CIE Standardphotopic observer with an f18 tolerance no greater than 3 %.Spectr
42、al correction filters to the V (l) function may be usedprovided that they are determined on material which has beenpreviously measured by spectroradiometric means and closelycorresponds in their spectral coefficient of retroreflection to thespecimen under test. See Annex A1 for uncertainty tests and
43、compensation.8.2.2 Photoreceptor Stability and LinearityThe stabilityand linearity of the photometric scale reading must be within1 % over the range of values to be measured (see Annex A2).The responsivity and range of the photoreceptor should besufficient such that readings of the projector light s
44、ource andthe retroreflector under test will have a resolution of at least 1part in 50.8.2.3 Photoreceptor Angular ApertureThe photoreceptormust be equipped with a means to limit the angular collectionof retroreflective luminous flux. This may be accomplishedwith an objective lens and field aperture
45、or with light baffling.The field of view shall be limited such that the effect of straylight is negligible. The field of view should be limited to thesmallest aperture that includes the entire test specimen or theilluminated area when testing horizontal coating materials.When an objective lens is us
46、ed, it shall be capable of focusingat the test distance.Angular apertures for the photoreceptor arespecified in degrees subtended at the specimen. The responsiv-ity across the aperture shall be uniform.8.3 Light Projector SourceThe light source shall be aprojector type capable of uniformly illuminat
47、ing the specimenwith appropriate reflector and lenses to provide illumination onthe test sample with a spectral power distribution conformingto the 1931 CIE Standard Illuminant Source A (a tungstenFIG. 2 View of Test Geometer for Measuring RetroreflectionE809083filament lamp operated at a correlated
48、 color temperature of2856K 620K, see Practice E 308). The normal illuminanceon the sample shall be uniform within 5 % of the averagenormal illuminance over the area of the retroreflector at the testdistance. The light projector shall be equipped with an adjust-able iris diaphragm or a selection of f
49、ixed apertures. Theintensity of light shall be regulated and shall not vary morethan 1 % for the duration of the test.8.3.1 The current of the projection lamp must be adjusted toprovide a correlated color temperature of 2856K. An adjust-ment procedure is described in Annex A3. Such adjustmentoften requires lowering the power from the nominal value sincemany projector lamps are designed to operate at correlatedcolor temperatures greater than 2856K.8.3.2 The size and shape of the projector exit aperture andthe angle this aperture subten
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