1、Designation: E 809 02Standard 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 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regul
5、atory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:E 284 Terminology of Appearance2E 308 Practice for Computing the Colors of Objects byUsing the CIE System2E 808 Practice for Describing Retroreflection22.2 CIE Documents:CIE Publication No. 54.2, RetroreflectionDefinition andMe
6、asurement3CIE Publication No. 17.4, International Lighting Vocabu-lary3CIE Publication No. 69-1987, Methods of CharacterizingIlluminance Meters and Luminance Meters33. Terminology3.1 Terms and definitions in Terminology E 284 and E 808are applicable to this practice. In general, the terminology inth
7、is practice agrees with that in CIE Publications 17.4 and 54.2.3.2 Definitions of Terms Specific to This Standard:3.2.1 retroreflectometer aperture angles the maximumangular diameter of the pencil of light (see Fig. 1).3.2.1.1 DiscussionIn practice the illumination arrives atthe retroreflector cente
8、r 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 angular diameter of the pencil is the“aperture angle.” It
9、 is generally assumed that the aperturefunctions are rotationally symmetrical and even uniform, butthis is often false, especially for illumination.3.2.2 retroreflector aperture surfacethe aperture surfaceof a retroreflector is given by the retroreflector itself, or by adiaphragm enclosing part of t
10、he retroreflector.3.2.3 retroreflector (or specimen) apertureangular dimen-sions from the source point of reference to the aperture surfaceof the retroreflector (or specimen).3.2.3.1 DiscussionAs the source and receiver are gener-ally close to each other, distinction is not made betweenaperture angl
11、es 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 describes the maximum variation of theentrance angle of the aperture surface of the retroreflector.3.2.4
12、 circular aperturethe angular diameter of a circularaperture surface.3.2.5 annular aperturethe difference between the angulardiameters of the external boundary circle and the internalboundary circle.3.2.6 rectangular aperturethe angular height and width ofa rectangular aperture surface.3.2.6.1 Discu
13、ssionThe orientation of the sides of therectangular aperture surface should be supplied together withthe angular height and width.3.2.7 source apertureangular dimensions from the ret-roreflector center to the exit aperture stop or pupil of the lightsource.3.2.8 receiver apertureangular dimensions fr
14、om the ret-roreflector center to the entrance aperture or pupil of thereceiver.1This 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 June 10, 2002. Published August 20
15、02. Originallypublished as E 809 81. Last previous edition E 809 94a (2000).2Annual Book of ASTM Standards, Vol 06.01.3Available from USNC/CIE Publications Office; TLA Lighting Consultants,Inc., 77 Pond St., Salem, MA 01970.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Cons
16、hohocken, PA 19428-2959, United States.3.2.9 retroreflector element apertureangular dimension ofthe aperture surface of a retroreflective element as seen fromthe receivers center.3.2.9.1 DiscussionThe element aperture quantifies an er-ror source in the setting of the observation angle. This is acrit
17、ical 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.3.2.10 goniometeran instrument for measuring or settingangles.3.2.11 photopic receivera
18、 receiver of radiation with aspectral responsivity which conforms to the V (l) distributionof the CIE Photopic Standard Observer that is specified inPractice E 308.3.2.12 reflected illuminance, Erilluminance at the re-ceiver measured on a plane perpendicular to the observationaxis.3.2.12.1 Discussio
19、nThis quantity is used in the calcula-tion of the coefficient of luminous intensity,RI: RI=(I/E)=(Erd2)/E, where d is the distance from theretroreflector to the receptor.4. Summary of Practice4.1 The fundamental procedure described in this practiceinvolves measurements of retroreflection based on th
20、e 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 quantitiesapplicable to retroreflectors can be determin
21、ed.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 measurephotometric quantities that relate to the visual p
22、erception 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 the receptorhas the photopic, V (l), spectral respo
23、nsivity 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 Applications6.1 Coeffcient of Retroreflection This
24、 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 useful engineeringquantity for determining the photome
25、tric 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 performance.6.2 Coeffcient of Luminous IntensityThis t
26、erm 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, taillightreflex reflectors and roadway delineators.6
27、.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 length.6.4 Reflectance Factor (of a Plane Reflecti
28、ng 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 BaSO4can have a reflectance factor much higher than o
29、ne (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 considers the retroreflector asa surface source who
30、se 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. It is recommended for describ-ing the performance
31、 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,RFThis measurement is used to evaluate retroreflectors onthe basis of flux ratios. It is numerically very nearly equal tothe coefficien
32、t of retroreflected luminance at small entranceangles. It is recommended for use in the design of retroreflec-tors but not for specification purposes.7. Requirements When Measuring Retroreflectors7.1 When describing photometric measurements of retrore-flectors, items in paragraphs 7.1.1-7.1.11 must
33、be included.Refer to Fig. 2 for a diagram of measurement geometryterminology.7.1.1 Retroreflective photometric quantity, such as: coeffi-cient of luminous intensity (RI), coefficient of retroreflectedluminance (RL) (also called specific luminance), coefficient ofFIG. 1 Illustration of Apertures used
34、 in RetroreflectionMeasurementE809022retroreflection (RA), coefficient of line retroreflection (RM),reflectance factor (RF), or coefficient of luminous 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 qua
35、ntity 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 near 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 Ro
36、tation 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 Source angular aperture.7.1.10 Retroreflector cen
37、ter.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 withrespect to the illumination direction.8. Apparat
38、us8.1 GeneralThe apparatus shall consist of a photorecep-tor, a light projector source, a specimen goniometer, anobserver goniometer, (sometimes known as the observationangle positioner), and a photometric range.8.1.1 Aperture angles are a very important considerationwhen measuring retroreflectors a
39、s Fig. 1 illustrates. The toler-ances recommended in the following paragraphs are to be usedgenerally, but materials may differ and in certain cases greaterrestriction on these aperture angles are necessary. See Table 1for recommendations for maximum angular aperture of opticalelements.8.2 Photorece
40、ptorThe 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 %.Spectral cor
41、rection 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 andcompen
42、sation.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 source
43、andthe retroreflector under test will have a resolution of at least 1part in 50.8.2.3 Photoreceptor Angular Aperture The 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 wi
44、th 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 used, i
45、t 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 illuminating
46、the specimenFIG. 2 View of Test Geometer for Measuring RetroreflectionTABLE 1 Optical Element Angular AperturesAStandard apertures 0.05 0.1 0.167 0.333Angular aperture of an individualretroreflective element, 0.01max0.02max0.04max0.08maxAOptical element angular aperture maximum requirements apply to
47、 all non-collimating instruments.E809023with appropriate reflector 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 620K, see Prac
48、tice 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 fixed apertures. Theintensity of light sha
49、ll 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 subtends at the test specimen must bes
