1、Designation: E 2540 08Standard Test Method forMeasurement of Retroreflective Signs Using a PortableRetroreflectometer at a 0.5 Degree Observation Angle1This standard is issued under the fixed designation E 2540; the number immediately following the designation indicates the year oforiginal adoption
2、or, in the case of revision, the year 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 test method covers measurement of the retroreflec-tive properties of sig
3、n materials such as traffic signs andsymbols (vertical surfaces) using a portable retroreflectometerthat can be used in the field. The portable retroreflectometer isa hand-held instrument with a defined standard geometry thatcan be placed in contact with sign material to measure theretroreflection i
4、n a standard geometry. The measurements canbe compared to minimum requirements to determine the needfor replacement. Entrance and observation angles specified inthis test method are those used currently in the United Statesand may differ from the angles used elsewhere in the world.1.2 This test meth
5、od is intended to be used for the fieldmeasurement of traffic signs but may be used to measure theperformance of materials before placing the sign in the field orbefore placing the sign material on the sign face.1.3 The values stated in SI units are to be regarded asstandard. No other units of measu
6、rement are included in thisstandard.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 regulatory limi
7、tations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 284 Terminology of AppearanceE 808 Practice for Describing RetroreflectionE 809 Practice for Measuring Photometric Characteristicsof RetroreflectorsE 810 Test Method for Coefficient of Retroreflection ofRetroreflective Sheeting Utiliz
8、ing the Coplanar Geometry3. Terminology3.1 The terminology used in this test method generallyagrees with that used in Terminology E 284.3.2 DefinitionsThe delimiting phrase “in retroreflection”applies to each of the following definitions when used outsidethe context of this or other retroreflection
9、standards.3.2.1 annular geometry, nthe portable instrumentretroreflection collection method where the retroreflected fluxis collected in an annulus 0.1 degrees wide centered on theillumination axis.3.2.1.1 DiscussionThe angle measured from the illumina-tion axis to the circle which divides the annul
10、us into equalareas corresponds to a specific observation angle.3.2.2 coeffcient of retroreflection, RA, nof a plane retrore-flecting surface, the ratio of the coefficient of luminousintensity (RI) of a plane retroreflecting surface to its area (A),expressed in candelas per lux per square metre (cd l
11、x1m2).3.2.3 datum axis, na designated half-line from the retrore-flector center perpendicular to the retroreflector axis.3.2.4 entrance angle, b, nthe angle between the illumi-nation axis and the retroreflector axis.3.2.5 entrance half-plane, nthe half plane that originateson the line of the illumin
12、ation axis and contains the retrore-flector axis.3.2.6 instrument standard, nworking standard used tostandardize the portable retroreflectometer.3.2.7 observation angle, a, nthe angle between the illu-mination axis and the observation axis.3.2.8 observation half-plane, nthe half plane that origi-nat
13、es on the line of the illumination axis and contains theobservation axis.3.2.9 orientation angle, vs, nthe angle in a plane perpen-dicular to the retroreflector axis from the entrance half-plane tothe datum axis, measured counter-clockwise from the view-point of the source1This test method is under
14、the jurisdiction of ASTM Committee E12 on Colorand Appearance and is the direct responsibility of Subcommittee E12.10 onRetroreflection.Current edition approved April 15, 2008. Published May 2008.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at
15、 serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.10 portable retroreflectometer, na hand-held i
16、nstru-ment that can be used in the field or in the laboratory formeasurement of retroreflectance.3.2.10.1 DiscussionIn this test method, “portable retrore-flectometer” refers to a hand-held instrument that can be placedin contact with sign material to measure the retroreflection in astandard geometr
17、y.3.2.11 presentation angle, g, nthe dihedral angle from theentrance half-plane to the observation half-plane, measuredcounter-clockwise from the viewpoint of the source.3.2.12 retroreflection, na reflection in which the reflectedrays are returned preferentially in directions close to theopposite of
18、 the direction of the incident rays, this propertybeing maintained over wide variations of the direction of theincident rays.3.2.13 rotation angle, , nthe angle in a plane perpen-dicular to the retroreflector axis from the observation half-plane to the datum axis, measured counter-clockwise from the
19、viewpoint of the source.3.3 Definitions of entrance angle components b1and b2,aswell as other geometrical terms undefined in this test method,may be found in Practice E 808.4. Summary of Test Method4.1 This test method involves the use of commercialportable retroreflectometers for determining the re
20、troreflectiv-ity of highway signing materials.4.2 The entrance angle shall be 4.4.3 The observation angle shall be 0.5.4.4 The portable retroreflectometer uses an instrumentstandard for standardization.4.5 After standardization, the retroreflectometer is placed incontact with the sign to be tested,
21、ensuring that only the desiredportion of the sign is within the measurement area of theinstrument.4.6 The reading displayed by the retroreflectometer isrecorded. The retroreflectometer is then moved to anotherposition on the sign, and this value is recorded. A minimum offour readings shall be taken
22、and averaged for each retroreflec-tive color on the sign to be tested.5. Significance and Use5.1 Measurements made by this test method are related tothe night time brightness of retroreflective traffic signs approxi-mately facing the driver of a mid-sized automobile equippedwith tungsten filament he
23、adlights at about 100 m distance.5.2 Retroreflective material used on traffic signs degradeswith time and requires periodic measurement to ensure that theperformance of the retroflection provides adequate safety to thedriver.5.3 The quality of the sign as to material used, age, andwear pattern will
24、have an effect on the coefficient of retrore-flection. These conditions need to be observed and noted by theuser.5.4 This test method is not intended for use for the mea-surement of signs when the instrument entrance and observa-tion angles differ from those specified herein.6. Apparatus6.1 Portable
25、 RetroreflectometerThe retroreflectometershall be portable, with the capability of being placed at variouslocations on the signs. The retroreflectometer shall be con-structed so that placement on the sign will preclude stray light(daylight) from entering the measurement area of the instru-ment and a
26、ffecting the reading.6.2 Instrument Standard, or standards of desired color(s)and material(s).6.3 Light Source Requirements:6.3.1 The projection optics shall be such that the illumi-nance at any point over the measurement area shall be within10 % of the average illuminance.6.3.2 The aperture angle o
27、f the source as determined fromthe center of the measurement area shall be not greater than0.1.6.4 Receiver Requirements:6.4.1 The receiver shall have sufficient sensitivity and rangeto accommodate coefficient of retroreflection values from 0.1to 1999.9 cd lx1m2.6.4.2 The combined spectral distribut
28、ion of the light sourceand the spectral responsivity of the receiver shall match thecombined spectral distribution of CIE Illuminant A and theV(l) spectral luminous efficiency function according to thefollowing criterion: For any choice of plano-parallel coloredabsorptive filter mounted in front of
29、a white retroreflectivesample, the ratio of the RAmeasured with the filter to the RAmeasured without the filter shall be within 10 % of theIlluminant A luminous transmittance of an air spaced pair oftwo such filters.6.4.3 The instrument may be either an instrument with pointgeometry, a “point instru
30、ment,” or an instrument with annulargeometry, an “annular instrument,” depending on the shape ofthe receiver aperture (see Fig. 1). Point and annular instrumentsmake geometrically different measurements of RA, which mayproduce values differing on the order of 10 %. Both measure-ments are valid for m
31、ost purposes, but the user should learn thetype of instrument from its specifications sheet and be aware ofcertain differences in operation and interpretation. For bothinstrument types, the “up” position of the instrument shall beknown. Both types of instruments may make additional mea-surements at
32、observation angles other than the 0.5 degree ofthis specification and combine the measurement at two or moredifferent observation angles if the readings at the differentobservation angles are reported separately.6.4.3.1 The point instrument makes an RAmeasurementwith the source and receiver geometry
33、 virtually identical to anRAmeasurement made on a range instrument following theprocedure of Test Method E 810. The 4 entrance angle wouldbe set on a range instrument by setting b1=4; b2=0. Thismay be called “4 entrance angle.” The rotation angle () forthe point instrument is determined by the angul
34、ar position ofthe instrument on the sign face. Assuming the retroreflectorsdatum axis to be upward, the rotation angle equals 0 when theinstrument is upright. Clockwise rotation of the instrument onthe sign face increases the rotation angle.E25400826.4.3.2 For the point instrument the “up” marking s
35、hall beopposite the entrance half-plane. It shall be in the observationhalf-plane (see Fig. 2).6.4.3.3 The annular instrument makes an RAmeasurementsimilar to an average of a great number of RAmeasurements ona range instrument with presentation angle (g) varying between180 and +180. For the 4 entran
36、ce angle the range instru-ment would include the b1and b2settings indicated in Table 1.There is no definite rotation angle () for the annular instru-ment. All values from 180 to +180 are included in themeasurement.6.4.3.4 For the annular instrument the “up” marking shall beopposite the entrance half
37、-plane (see Fig. 2).6.4.3.5 For both instrument types, the orientation angle (vs)is determined by the angular position of the instrument on thesign face. It is the rotation angle () rather than the orientationangle (vs) which primarily affects retroreflection of signsmeasured at the small 4 entrance
38、 angle.6.4.3.6 Rotationally insensitive sheetings, such as glassbead sheetings, have RAvalues that are nearly independent ofFIG. 1 Annular and Point Aperture Instrument AnglesNOTE 1For each instrument type, the illumination beam is 4 down-ward. For the point instrument, receiver is above source.FIG.
39、 2 Upright Optical SchematicsTABLE 1 Laboratory Emulation of Annular Instrument Geometryab1b20.5 3.86 1.03 1650.5 3.47 2.00 1500.5 2.83 2.83 1350.5 2.00 3.46 1200.5 1.04 3.86 1050.5 0.00 4.00 900.5 1.04 3.86 750.5 2.00 3.46 600.5 2.83 2.83 450.5 3.47 2.00 300.5 3.86 1.03 150.5 4.00 0.00 00.5 3.86 1.
40、03 150.5 3.47 2.00 300.5 2.83 2.83 450.5 2.00 3.46 600.5 1.04 3.86 750.5 0.00 4.00 900.5 1.04 3.86 1050.5 2.00 3.46 1200.5 2.83 2.83 1350.5 3.47 2.00 1500.5 3.86 1.03 1650.5 4.00 0.00 180E2540083the rotation angle. Accordingly, the point and annular instru-ments will make practically identical measu
41、rements of RAforsigns made with such sheetings.6.4.3.7 Most prismatic retroreflectors are rotationally sensi-tive, having RAvalues that vary significantly with rotationangle (), even at small entrance angles. The difference of RAmeasurements made with the two types of instrument onprismatic signs ma
42、y become as great as 20 % in extreme cases,but is generally on the order of 10 %. Neither the magnitudenor the direction of difference can be predicted for unknownsamples. Thus, critical comparison of prismatic sign RAvaluesmeasured by instruments of the two types is not recommended.6.4.3.8 A point
43、instrument can gage the variation of RAwithrotation angle by placing it with different angular positionsupon the sign face. RAvariation of 5 % for 5 rotation is notunusual. Accordingly, repeatable RAmeasurement of prismaticsigns with a point instrument, requires care in angular posi-tioning.6.4.3.9
44、An annular instrument cannot gage the variation ofRAwith rotation angle. Accordingly, repeatable RAmeasure-ment of prismatic signs with an annular instrument does notrequire care in angular positioning. Positioning to within 615is sufficient.6.4.4 The aperture angle of the receiver as determined fro
45、mthe measurement area shall be not greater than 0.1. Theaperture angle of the receiver is measured from inner to outerring limits for annular receivers (see Fig. 1).6.4.5 The combined stability of the output of the lightsource and receiver shall not change more than 61 % after10 s when the retrorefl
46、ectometer is in contact with the signface.6.4.6 The linearity of the retroreflectometer photometricscale over the range of readings expected shall be within 2 %.Correction factors may be used to ensure a linear response. Amethod for determining linearity can be found in Annex A2 ofPractice E 809.6.5
47、 Measurement Geometry:6.5.1 The geometry used to determine the photometricperformance shall be in accordance with Practice E 808.6.5.2 The light source and receiver shall be at opticalinfinity and possess an observation angle of 0.5 6 0.01 (636arc seconds) as measured from the center of the source a
48、pertureto the centroid of responsivity of the receiver at all presentationangles. For annular receivers, the observation angle is taken asthe angular distance when areaAand area B are equal (see Fig.1). The reason for this collimation requirement is to accom-modate the correct measurement of large o
49、ptical elements inthe retroreflective sheeting as stated in 8.1.4.2 by maintaininga constant entrance angle over the sample area.6.5.3 The entrance angle of the light source shall be 4 6 1.7. Standardization7.1 The retroreflectometer shall be standardized using aninstrument standard consisting of a separate panel or disc of amaterial with a known RAvalue. The calibration values shall bemaintained by
