ASTM E1709-2008 Standard Test Method for Measurement of Retroreflective Signs Using a Portable Retroreflectometer at a 0 2 Degree Observation Angle.pdf

1、Designation: E 1709 08Standard Test Method forMeasurement of Retroreflective Signs Using a PortableRetroreflectometer at a 0.2 Degree Observation Angle1This standard is issued under the fixed designation E 1709; 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers measurement of the retroreflec-tive properties of si

3、gn 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

4、in 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 met

5、hod 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 This standard does not purport to address all of thesafety concerns, if any, associ

6、ated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and to determine theapplicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 284 Terminology of AppearanceE 808 Practice for Describi

7、ng RetroreflectionE 809 Practice for Measuring Photometric Characteristicsof RetroreflectorsE 810 Test Method for Coefficient of Retroreflection ofRetroreflective Sheeting Utilizing the Coplanar Geometry3. Terminology3.1 The terminology used in this test method generallyagrees with that used in Term

8、inology 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 standards.3.2.1 annular geometry, nthe portable instrument retrore-flection collection method where an annular area 0.1 de

9、greeswide around the illumination axis collects the retroreflectedenergy at an angle to the center of the annular area correspond-ing 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)

10、of a plane retroreflecting surface to its area (A),expressed in candelas per lux per square metre (cd lx1m2).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 r

11、etroreflector axis.3.2.5 entrance half-plane, nthe half plane that originateson the line of the illumination 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 i

12、llu-mination axis and the observation axis.3.2.8 observation half-plane, nthe half plane that origi-nates 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 to

13、the datum axis, measured counter-clockwise from the view-point of the source.3.2.10 portable retroreflectometer, na hand-held instru-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” refer

14、s to a hand-held instrument that can be placedin contact with sign material to measure the retroreflection in astandard geometry.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.1Th

15、is test method is under the jurisdiction of ASTM Committee E12 on Colorand Appearance and is the direct responsibility of Subcommittee E12.10 onRetroreflection.Current edition approved Feb. 1, 2008. Published March 2008. Originallyapproved in 1995. Last previous edition approved in 2000 as E 1709 00

16、e1.2For 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO B

17、ox C700, West Conshohocken, PA 19428-2959, United States.3.2.12 retroreflection, na reflection in which the reflectedrays are returned preferentially in directions close to theopposite of the direction of the incident rays, this propertybeing maintained over wide variations of the direction of thein

18、cident rays.3.2.13 rotation angle, e, nthe angle in a plane perpendicu-lar to the retroreflector axis from the observation half-plane tothe datum axis, measured counter-clockwise from the view-point of the source.3.3 Definitions of entrance angle components b1and b2,aswell as other geometrical terms

19、 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 commercial por-table retroreflectometers for determining the retroreflectivity ofhighway signing materials.4.2 The entrance angle shall be 4.4.3 The observation angle shall

20、 be 0.2.4.4 The portable retroreflectometer uses a instrument stan-dard for standardization.4.5 After standardization, the retroreflectometer is placed incontact with the sign to be tested, ensuring that only the desiredportion of the sign is within the measurement area of theinstrument.4.6 The read

21、ing displayed by the retroreflectometer is re-corded. The retroreflectometer is then moved to anotherposition on the sign, and this value is recorded. A minimum offour readings shall be taken and averaged for each retroreflec-tive color on the sign to be tested.5. Significance and Use5.1 Measurement

22、s 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 headlights at about 200 m distance.5.2 Retroreflective material used on traffic signs degradeswith time and re

23、quires 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, and wearpattern will have an effect on the coefficient of retroreflection.These conditions need to be observed and noted by the u

24、ser.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 RetroreflectometerThe retroreflectometershall be portable, with the capability of being placed at variousloc

25、ations 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 affecting the reading.6.2 Instrument Standard, or standards of desired color(s)and material(s).6.3 Light Sourc

26、e 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 of the source as determined fromthe center of the measurement area shall be not greater than0.1.6.4 Receiver R

27、equirements: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 distribution of the light sourceand the spectral responsivity of the receiver shall match thecombined spectral distrib

28、ution 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 a white retroreflectivesample, the ratio of the RAmeasured with the filter to the RAmeasured without the filt

29、er shall be within 10 % of theIlluminantAluminous transmittance of an air space pair of twosuch filters.6.4.3 The instrument may be either a “point instrument” oran “annular instrument,” depending on the shape of thereceiver aperture (see Fig. 1). Point and annular instrumentsmake geometrically diff

30、erent measurements of RA, which mayproduce values differing on the order of 10 %. Both measure-ments are valid for most 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

31、, the “up” position of the instrument shall beknown. Both types of instruments may make additional mea-surements at 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 ang

32、les are reported separately.6.4.3.1 The point instrument makes an RAmeasurementvirtually identical to an RAmeasurement made on a rangeinstrument following the procedure of Test Method E 810. The4 entrance angle would be set on a range instrument bysetting b1=4; b2=0. This may be called “-4 entrancea

33、ngle.” The rotation angle (e) for the point instrument isdetermined by the angular position of the instrument on thesign face. Assuming the retroreflectors datum axis to beupward, the rotation angle equals 0 when the instrument isupright. Clockwise rotation of the instrument on the sign faceincrease

34、s the rotation angle.6.4.3.2 For the point instrument the “up” marking shall 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 w

35、ith presentation angle (g) varying between180 and +180. For the 4 entrance angle the rangeinstrument would include the b1and b2settings indicated inTable 1. There is no definite rotation angle (e) for the annularinstrument. All values from 180 to +180 are included in themeasurement.6.4.3.4 For the a

36、nnular instrument the “up” marking shall beopposite the entrance half-plane (see Fig. 2).E17090826.4.3.5 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 (e) rather than the orientationangle (vs) wh

37、ich primarily affects retroreflection of signsmeasured at the small 4 entrance angle.6.4.3.6 Rotationally insensitive sheetings, such as glassbead sheetings, have RAvalues that are nearly independent ofthe rotation angle. Accordingly, the point and annular instru-ments will make practically identica

38、l measurements of RAforsigns made with such sheetings.6.4.3.7 Most prismatic retroreflectors are rotationally sensi-tive, having RAvalues that vary significantly with rotationangle (e), even at small entrance angles. The difference of RAmeasurements made with the two types of instrument onprismatic

39、signs may become as great as 25 % 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

40、Apoint 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

41、.4.3.9 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.FIG. 1 Annular and Point Aperture Instrument Angles

42、NOTE 1For each instrument type, the illumination beam is 4 down-ward For the point instrument, receiver is above source.FIG. 2 Upright Optical SchematicsTABLE 1 Laboratory Emulation of Annular Instrument Geometryab1b2e0.2 3.86 1.03 1650.2 3.47 2.00 1500.2 2.83 2.83 1350.2 2.00 3.46 1200.2 1.04 3.86

43、1050.2 0.00 4.00 900.2 1.04 3.86 750.2 2.00 3.46 600.2 2.83 2.83 450.2 3.47 2.00 300.2 3.86 1.03 150.2 4.00 0.00 00.2 3.86 1.03 150.2 3.47 2.00 300.2 2.83 2.83 450.2 2.00 3.46 600.2 1.04 3.86 750.2 0.00 4.00 900.2 1.04 3.86 1050.2 2.00 3.46 1200.2 2.83 2.83 1350.2 3.47 2.00 1500.2 3.86 1.03 1650.2 4

44、.00 0.00 180E17090836.4.4 The aperture angle of the receiver as determined fromthe 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 lightso

45、urce and receiver shall not change more than 61 % after10 s when the retroreflectometer 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. A

46、method for determining linearity can be found in Annex A2 ofPractice E 809.6.5 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 (collimated) and possess an o

47、bservation angle of 0.56 0.01 (6 36 arc seconds) as measured from the center of thesource aperture to the centroid of responsivity of the receiver atall presentation angles. For annular receivers, the observationangle is taken as the angular distance when area A and area Bare equal (see Fig. 1). The

48、re are two independent reasons forthis collimation requirement. The first reason for this collima-tion requirement is to avoid an observation angle error inmeasurements or retroreflective signs consisting of large opti-cal elements as described in 8.1.4.2. The second reason for thecollimation requir

49、ement is to maintain a constant entranceangle over the sample area.6.5.3 The entrance angle of the light source shall be4 61.7. 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 checking against other standards or by labora-tory recalibration s