1、Designation: E2540 08E2540 16Standard Test Method forMeasurement of Retroreflective Signs Using a PortableRetroreflectometer at a 0.5 Degree Observation Angle1This standard is issued under the fixed designation E2540; the number immediately following the designation indicates the year oforiginal ado
2、ption 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 retroreflective properties o
3、f sign materials such as traffic signs and symbols(vertical surfaces) using a portable retroreflectometer that can be used in the field. The portable retroreflectometer is a hand-heldinstrument with a defined standard geometry that can be placed in contact with sign material to measure the retrorefl
4、ection in astandard geometry. The measurements can be compared to minimum requirements to determine the need for replacement. Entranceand observation angles specified in this test method are those used currently in the United States and may differ from the anglesused elsewhere in the world.1.2 This
5、test method is intended to be used for the field measurement of traffic signs but may be used to measure theperformance of materials before placing the sign in the field or before placing the sign material on the sign face.1.3 The values stated in SI units are to be regarded as standard. No other un
6、its of measurement are included in this standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of reg
7、ulatorylimitations prior to use.1.5 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organ
8、ization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E177 Practice for Use of the Terms Precision and Bias in ASTM Test MethodsE284 Terminology of AppearanceE691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test MethodE808
9、 Practice for Describing RetroreflectionE809 Practice for Measuring Photometric Characteristics of RetroreflectorsE810 Test Method for Coefficient of Retroreflection of Retroreflective Sheeting Utilizing the Coplanar Geometry3. Terminology3.1 The terminology used in this test method generally agrees
10、 with that used in Terminology E284.3.2 DefinitionsThe delimiting phrase “in retroreflection” applies to each of the following definitions when used outside thecontext of this or other retroreflection standards.3.2.1 annular geometry, nthe portable instrument retroreflection collection method where
11、the retroreflected lux is collected inan annulus 0.1 degrees wide centered on the illumination axis.3.2.1.1 Discussion1 This test method is under the jurisdiction ofASTM Committee E12 on Color andAppearance and is the direct responsibility of Subcommittee E12.10 on Retroreflection.Current edition ap
12、proved April 15, 2008Nov. 1, 2016. Published May 2008April 2017. Originally approved in 2008. Last previous edition approved in 2008 as E2540 08. DOI: 10.1520/E2540-08.10.1520/E2540-16.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm
13、org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
14、it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr
15、 Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1The angle measured from the illumination axis to the circle which divides the annulus into equal areas corresponds to a specificobservation angle.3.2.2 coeffcient of retroreflection, RA, nof a plane retroreflecting surface,
16、the ratio of the coefficient of luminous intensity (RI)of a plane retroreflecting surface to its area (A), expressed in candelas per lux per square metre (cd lx1 m2).3.2.3 datum axis, na designated half-line from the retroreflector center perpendicular to the retroreflector axis.3.2.4 entrance angle
17、 , nthe angle between the illumination axis and the retroreflector axis.3.2.5 entrance half-plane, nthe half plane that originates on the line of the illumination axis and contains the retroreflectoraxis.3.2.6 instrument standard, nworking standard used to standardize the portable retroreflectomete
18、r.3.2.7 observation angle, , nthe angle between the illumination axis and the observation axis.3.2.8 observation half-plane, nthe half plane that originates on the line of the illumination axis and contains the observationaxis.3.2.9 orientation angle, s, nthe angle in a plane perpendicular to the re
19、troreflector axis from the entrance half-plane to thedatum axis, measured counter-clockwise from the viewpoint of the source.3.2.10 portable retroreflectometer, na hand-held instrument that can be used in the field or in the laboratory for measurementof retroreflectance.3.2.10.1 DiscussionIn this te
20、st method, “portable retroreflectometer” refers to a hand-held instrument that can be placed in contact with sign materialto measure the retroreflection in a standard geometry.3.2.11 presentation angle, , nthe dihedral angle from the entrance half-plane to the observation half-plane, measuredcounter
21、clockwise from the viewpoint of the source.3.2.12 retroreflection, na reflection in which the reflected rays are returned preferentially in directions close to the oppositeof the direction of the incident rays, this property being maintained over wide variations of the direction of the incident ray
22、s.3.2.13 rotation angle, , nthe angle in a plane perpendicular to the retroreflector axis from the observation half-plane to thedatum axis, measured counter-clockwise from the viewpoint of the source.3.3 Definitions of entrance angle components 1 and 2, as well as other geometrical terms undefined i
23、n this test method, maybe found in Practice E808.4. Summary of Test Method4.1 This test method involves the use of commercial portable retroreflectometers for determining the retroreflectivity ofhighway signing materials.4.2 The entrance angle shall be 4.4.4.3 The observation angle shall be 0.5.4.4
24、The portable retroreflectometer uses an instrument standard for standardization.4.5 After standardization, the retroreflectometer is placed in contact with the sign to be tested, ensuring that only the desiredportion of the sign is within the measurement area of the instrument.4.6 The reading displa
25、yed by the retroreflectometer is recorded. The retroreflectometer is then moved to another position onthe sign, and this value is recorded. A minimum of four readings shall be taken and averaged for each retroreflective color on thesign to be tested.5. Significance and Use5.1 Measurements made by th
26、is test method are related to the night time brightness of retroreflective traffic signs approximatelyfacing the driver of a mid-sized automobile equipped with tungsten filament headlights at about 100 m distance.5.2 Retroreflective material used on traffic signs degrades with time and requires peri
27、odic measurement to ensure that theperformance of the retroflection provides adequate safety to the driver.5.3 The quality of the sign as to material used, age, and wear pattern will have an effect on the coefficient of retroreflection.These conditions need to be observed and noted by the user.5.4 T
28、his test method is not intended for use for the measurement of signs when the instrument entrance and observation anglesdiffer from those specified herein.E2540 1626. Apparatus6.1 Portable RetroreflectometerThe retroreflectometer shall be portable, with the capability of being placed at variouslocat
29、ions on the signs. The retroreflectometer shall be constructed so that placement on the sign will preclude stray light (daylight)from entering the measurement area of the instrument and affecting the reading.6.2 Instrument Standard, or standards of desired color(s) and material(s).6.3 Light Source R
30、equirements:6.3.1 The projection optics shall be such that the illuminance at any point over the measurement area shall be within 10 % ofthe average illuminance.6.3.2 The aperture angle of the source as determined from the center of the measurement area shall be not greater than 0.1.6.4 Receiver Req
31、uirements:6.4.1 The receiver shall have sufficient sensitivity and range to accommodate coefficient of retroreflection values from 0.1 to1999.9 cd lx1 m2.6.4.2 The combined spectral distribution of the light source and the spectral responsivity of the receiver shall match thecombined spectral distri
32、bution of CIE Illuminant A and the V() spectral luminous efficiency function according to the followingcriterion: For any choice of plano-parallel colored absorptive filter mounted in front of a white retroreflective sample, the ratio ofthe RA measured with the filter to the RA measured without the
33、filter shall be within 10 % of the Illuminant A luminoustransmittance of an air spaced pair of two such filters.6.4.3 The instrument may be either an instrument with point geometry, a “point instrument,” or an instrument with annulargeometry, an “annular instrument,” depending on the shape of the re
34、ceiver aperture (see Fig. 1). Point and annular instrumentsmake geometrically different measurements of RA, which may produce values differing on the order of 10 %. Both measurementsare valid for most purposes, but the user should learn the type of instrument from its specifications sheet and be awa
35、re of certaindifferences in operation and interpretation. For both instrument types, the “up” position of the instrument shall be known. Bothtypes of instruments may make additional measurements at observation angles other than the 0.5 degree of this specification andcombine the measurement at two o
36、r more different observation angles if the readings at the different observation angles are reportedseparately.6.4.3.1 The point instrument makes an RA measurement with the source and receiver geometry virtually identical to an RAmeasurement made on a range instrument following the procedure of Test
37、 Method E810. The 4 entrance angle would be set ona range instrument by setting 1 =4; 2 =0. This may be called “4 entrance angle.” The rotation angle () for the pointinstrument is determined by the angular position of the instrument on the sign face. Assuming the retroreflectors datum axis tobe upwa
38、rd, the rotation angle equals 0 when the instrument is upright. Clockwise rotation of the instrument on the sign faceincreases the rotation angle.6.4.3.2 For the point instrument the “up” marking shall be opposite the entrance half-plane. It shall be in the observationhalf-plane (see Fig. 2).FIG. 1
39、Annular and Point Aperture Instrument AnglesE2540 1636.4.3.3 The annular instrument makes an RA measurement similar to an average of a great number of RA measurements on arange instrument with presentation angle () varying between 180 and +180. For the 4 entrance angle the range instrumentwould incl
40、ude the 1 and 2 settings indicated in Table 1. There is no definite rotation angle () for the annular instrument. Allvalues from 180 to +180 are included in the measurement.6.4.3.4 For the annular instrument the “up” marking shall be opposite the entrance half-plane (see Fig. 2).6.4.3.5 For both ins
41、trument types, the orientation angle (s) is determined by the angular position of the instrument on the signface. It is the rotation angle () rather than the orientation angle (s) which primarily affects retroreflection of signs measured atthe small 4 entrance angle.NOTE 1For each instrument type, t
42、he illumination beam is 4 downward. For the point instrument, receiver is above source.FIG. 2 Upright Optical SchematicsTABLE 1 Laboratory Emulation of Annular Instrument Geometry 1 2 0.5 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 7
43、50.5 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 1.03 150.5 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 180E2540 1646.4.3.6 Rotat
44、ionally insensitive sheetings, such as glass bead sheetings, have RA values that are nearly independent of therotation angle. Accordingly, the point and annular instruments will make practically identical measurements of RA for signs madewith such sheetings.6.4.3.7 Most prismatic retroreflectors are
45、 rotationally sensitive, having RA values that vary significantly with rotation angle (),even at small entrance angles. The difference of RA measurements made with the two types of instrument on prismatic signs maybecome as great as 20 % in extreme cases, but is generally on the order of 10 %. Neith
46、er the magnitude nor the direction ofdifference can be predicted for unknown samples. Thus, critical comparison of prismatic sign RA values measured by instrumentsof the two types is not recommended.6.4.3.8 A point instrument can gage the variation of RA with rotation angle by placing it with differ
47、ent angular positions uponthe sign face. RA variation of 5 % for 5 rotation is not unusual. Accordingly, repeatable RA measurement of prismatic signs witha point instrument, requires care in angular positioning.6.4.3.9 An annular instrument cannot gage the variation of RA with rotation angle. Accord
48、ingly, repeatable RA measurement ofprismatic signs with an annular instrument does not require care in angular positioning. Positioning to within 615 is sufficient.6.4.4 The aperture angle of the receiver as determined from the measurement area shall be not greater than 0.1. The apertureangle of the
49、 receiver is measured from inner to outer ring limits for annular receivers (see Fig. 1).6.4.5 The combined stability of the output of the light source and receiver shall not change more than 61 % after10 s when the retroreflectometer is in contact with the sign face.6.4.6 The linearity of the retroreflectometer photometric scale over the range of readings expected shall be
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