1、Designation: E809 08 (Reapproved 2013)Standard Practice forMeasuring Photometric Characteristics of Retroreflectors1This standard is issued under the fixed designation E809; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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 ofr
3、etroreflective 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 E808.1.3 This practice describes the parameters that are requiredwhen stating photometric measureme
4、nts in specific 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 ther
5、esponsibility 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:2E284 Terminology of AppearanceE308 Practice for Computing the Colors of Objects by Using
6、the CIE SystemE808 Practice for Describing Retroreflection2.2 CIE Documents:CIE Publication No. 54.2 RetroreflectionDefinition andMeasurement3CIE Publication DS 17.2/E:2009 International Lighting Vo-cabulary3CIE Publication No. 69-1987 Methods of CharacterizingIlluminance Meters and Luminance Meters
7、33. Terminology3.1 Terms and definitions in Terminology E284 and E808are applicable to this practice. In general, the terminology inthis practice agrees with that in CIE Publications DS 17.2/E:2009 and 54.2.3.2 Definitions of Terms Specific to This Standard:3.2.1 annular aperture, nthe difference be
8、tween the an-gular diameters 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
9、 responsivity which conforms to the V () distributionof the CIE Photopic Standard Observer that is specified inPractice E308.3.2.5 receiver aperture, nangular dimensions from theretroreflector center to the entrance aperture or pupil of thereceiver.3.2.6 rectangular aperture, nthe angular height and
10、 widthof a rectangular 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 observationaxi
11、s.3.2.7.1 DiscussionThis 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.
12、1 DiscussionIn practice 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”functio
13、n and the maximum angular diameter of the pencil is the“aperture angle.” It is generally assumed that the aperture1This 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
14、 Jan. 1, 2013. Published January 2013. Originallyapproved in 1981. Last previous edition approved in 2008 as E809 08. DOI:10.1520/E0809-08R13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards vol
15、ume information, refer to the standards Document Summary page onthe ASTM website.3Available from the CIE Webshop at http:/www.cie.co.at.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1functions are rotationally symmetrical and even un
16、iform, butthis is often false, especially for illumination.3.2.9 retroreflector aperture surface, nthe aperture surfaceof a retroreflector is given by the retroreflector itself, or by adiaphragm enclosing part of the retroreflector.3.2.10 retroreflector element aperture, nangular dimen-sion of the a
17、perture 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 acritical feature for testing large retroreflective elements or atshort distances. When using collimated op
18、tics, placing thesource and receiver at virtual infinity, the retroreflector elementaperture is virtually zero.3.2.11 retroreflector (or specimen) aperture, nangular di-mensions from the source point of reference to the aperturesurface of the retroreflector (or specimen).3.2.11.1 DiscussionAs the so
19、urce 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 virtualinfinity, the retroreflector aperture is virtually naught. Theretroreflector aperture descri
20、bes 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 of thelight source.4. Summary of Practice4.1 The fundamental procedure described in this practicei
21、nvolves 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 the retroreflector. From these measurements, alongwith the geometry of test, various photometric quan
22、titiesapplicable 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 substitution test method).5. Significance and Use5.1 This practice describes procedures used to measur
23、ephotometric quantities that relate to the visual perception ofretroreflected light. The most significant usage is in the relationto the nighttime vehicle headlamp, retroreflector, and driverseye geometry. For this reason the CIE Standard Source A isused to represent a tungsten vehicle headlamp and
24、the receptorhas the photopic, V (), spectral responsivity corresponding tothe light adapted human eye. Although the geometry must bespecified by the user, it will, in general, correspond to therelation between the vehicle headlamp, the retroreflector, andthe vehicle drivers eye position.6. Uses and
25、Applications6.1 Coeffcient of RetroreflectionThis quantity is used tospecify the performance of retroreflective sheeting. It considersthe retroreflector as an apparent point source whose retrore-flected luminous intensity is dependent on the area of theretroreflective surface involved. It is a usefu
26、l engineeringquantity for determining the photometric performance of suchretroreflective surfaces as highway delineators or warningdevices. The coefficient of retroreflection may also be used todetermine the minimum area of retroreflective sheeting neces-sary for a desired level of photometric perfo
27、rmance.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 illuminance incident on the device. It is recom-mended for use in describing performance of RPMs, tai
28、llightreflex 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 retroreflective materials,when the actual width is not as important as is the reflectivityper unit l
29、ength.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 diffuse reflectors. Since almost all naturalsurfaces tend to retroreflect slightly, materials such as BaSO
30、4can 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, for example, 45.6.5 Coeffcient of Retroreflected Luminance (also calledSpecific Luminance)This term co
31、nsiders 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 retroreflectivesurface is focused on the retina of the human eye and to thevisual effect thereby produced.
32、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 Unit Solid Angle,RThis measurement is used to evaluate retroreflectors onthe basis of flux ratios. It i
33、s 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.FIG. 1 Illustration of Apertures used in Retroreflection Measure-mentE809 08 (2013)27. Requirements Wh
34、en Measuring Retroreflectors7.1 When describing photometric measurements ofretroreflectors, items in paragraphs 7.1.1-7.1.11 must be in-cluded. Refer to Fig. 2 for a diagram of measurement geometryterminology.7.1.1 Retroreflective photometric quantity, such as: coeffi-cient of luminous intensity (RI
35、), coefficient of retroreflectedluminance (RL) (also called specific luminance), coefficient ofretroreflection (RA), coefficient of line retroreflection (RM),reflectance factor (RF), or coefficient of luminous flux per unitsolid angle (R).7.1.1.1 In specifications, a minimum acceptable quantitativev
36、alue 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, (1and 2).7.1.4.1 When both 1and 2are near zero, care must betaken to prevent specular reflection from entering the photore-ceptor.7.1.
37、4.2 Entrance angle equals cos1(cos1cos2).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 minimum test distance.7.1.7 Test specimen size and shape.7.1.8 Photoreceptor angular aperture.7.1.9
38、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 automobile or bicycle reflectors, theretroreflector axis and retroreflector center may be defined wit
39、hrespect to the illumination direction.8. Apparatus8.1 GeneralThe apparatus shall consist of aphotoreceptor, a light projector source, a specimen goniometer,an observer goniometer, (sometimes known as the observationangle positioner), and a photometric range.8.1.1 Aperture angles are a very importan
40、t 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 PhotoreceptorThe photoreceptor shall be equipped asfollows:8.2.1 Photopic FilterThe photoreceptor shall b
41、e equippedwith a light filter such that the spectral responsivity of thereceptor should match the V() response of the CIE Standardphotopic observer with an f1 tolerance no greater than 3 %.Spectral correction filters to the V() function may be usedprovided that they are determined on material which
42、has beenpreviously measured by spectroradiometric means and closelycorresponds in their spectral coefficient of retroreflection to thespecimen under test. See Annex A1 for uncertainty tests andcompensation.8.2.2 Photoreceptor Stability and LinearityThe stabilityand linearity of the photometric scale
43、 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 source andthe retroreflector under test will have a resolution of at least 1part in 50.8.2.3 Photoreceptor A
44、ngular 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 or with light baffling.The field of view shall be limited such that the effect of straylight is negligible.
45、 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 used, it shall be capable of focusingat the test distance.Angular apertures for the photoreceptor arespecifie
46、d in degrees subtended at the specimen. The responsiv-ity across the aperture shall be uniform.FIG. 2 View of Test Geometer for Measuring RetroreflectionE809 08 (2013)38.3 Light Projector SourceThe light source shall be aprojector type capable of uniformly illuminating the specimenwith appropriate r
47、eflector and lenses to provide illumination onthe test sample with a spectral power distribution conformingto the 1931 CIE Standard Illuminant Source A (a tungstenfilament lamp operated at a correlated color temperature of2856K 6 20K, see Practice E308).The normal illuminance onthe sample shall be u
48、niform within 5 % of the average normalilluminance 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 fixed apertures. Theintensity of light shall be regulated and shall not vary morethan 1 % for the dur
49、ation 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 subtends at the test specimen must bespecified. The radiance across the aperture shall b
