ASTM D4061-94(2006)
(Test Method)Standard Test Method for Retroreflectance of Horizontal Coatings
Standard Test Method for Retroreflectance of Horizontal Coatings
SIGNIFICANCE AND USE
The quantity coefficient of retroreflected luminance is a measure of the reflected luminance in the direction of the observer. This is the light returned by the retroreflective surface to the observer from the source, which in practice is the vehicle headlamp.
This test method may be used as a measure of the nighttime performance of horizontally applied surfacing materials used on highway surfaces for lane markings and other traffic control purposes.
Since this test method is a laboratory procedure, test specimens must be prepared so that they can be mounted on the specimen holder. Specimens measured by this laboratory method may be used as transfer standards for the calibration of portable instrumentation.
Specimen selection and preparation may significantly influence the results of this test method.
SCOPE
1.1 This test method describes the instrumental measurement of the retroreflective properties of horizontal surfacing materials, such as traffic stripe paint systems, traffic tapes, and traffic surface symbols.
1.2 Specimen preparation, size, and shape must be determined and specified by the user of this test method. Likewise, the user must specify the observation and entrance angles to be used (see ).
1.3 The geometric requirements of this test method are based on materials for which the relative retroreflectance changes less than approximately 50 % over the observation angle range from 0.2 to 0.5. This is illustrated in .
1.4 This test method is a laboratory test and requires a facility that can be darkened sufficiently so that stray light does not affect the test results. This facility must be capable of housing the required 15-m test distance.
1.5 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D4061 −94(Reapproved2006)
Standard Test Method for
Retroreflectance of Horizontal Coatings
This standard is issued under the fixed designation D4061; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E809Practice for Measuring Photometric Characteristics of
Retroreflectors
1.1 This test method describes the instrumental measure-
ment of the retroreflective properties of horizontal surfacing 2.2 CIE Publication:
materials, such as traffic stripe paint systems, traffic tapes, and No. 54Retroreflection Definition and Measurement
traffic surface symbols.
3. Terminology
1.2 Specimen preparation, size, and shape must be deter-
mined and specified by the user of this test method. Likewise, 3.1 The terms and definitions inTerminology E284 apply to
theusermustspecifytheobservationandentranceanglestobe this test method.
used (see Fig. 1).
3.2 Definitions:
1.3 The geometric requirements of this test method are 3.2.1 coeffıcient of retroreflected luminance, R ,n—ratio of
L
based on materials for which the relative retroreflectance the luminance, L, of a projected surface to the normal
changes less than approximately 50% over the observation illuminance, E , at the surface on a plane normal to the
'
incident light, expressed in candelas per square metre per lux
angle range from 0.2 to 0.5°. This is illustrated in Fig. 2.
−2
−1
(cd·m ·lx ).
1.4 This test method is a laboratory test and requires a
R 5 L/E (1)
facilitythatcanbedarkenedsufficientlysothatstraylightdoes ~ !
L '
not affect the test results. This facility must be capable of
3.2.2 datum mark, n—in retroreflection,anindicationonthe
housing the required 15-m test distance.
retroreflector that is used to define the orientation of the
retroreflector with respect to rotation about the retroreflector
1.5 The values stated in SI units are to be regarded as the
axis.
standard. The values given in parentheses are for information
3.2.2.1 Discussion—The datum mark must not lie on the
only.
retroreflector axis.
1.6 This standard does not purport to address all of the
3.2.3 entrance angle,β, n—in retroreflection,anglebetween
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- the illumination axis and the retroreflector axis.
3.2.3.1 Discussion—For plane retroreflective surfaces, the
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. entrance angle is no larger than 90°.
3.2.3.2 Discussion—Theentranceanglemaybedividedinto
2. Referenced Documents components β and β . This is described in Practice E808.In
1 2
2 this test method only the component β is used. Therefore,
2.1 ASTM Standards:
where only the entrance angle β is specified the convention
E284Terminology of Appearance
used is β =0 and β = β.
2 1
E308PracticeforComputingtheColorsofObjectsbyUsing
3.2.4 illumination axis, n— in retroreflection,alinefromthe
the CIE System
effective center of the source aperture to the retroreflector
E808Practice for Describing Retroreflection
center.
3.2.5 normal illuminance, E —theilluminanceonaretrore-
'
This test method is under the jurisdiction of ASTM Committee E12 on Color
flective surface measured in the plane that passes through the
and Appearance and is the direct responsibility of Subcommittee E12.10 on
retroreflector center and is perpendicular to the illumination
Retroreflection.
−2
axis; measured in lux (lumens·m ).
CurrenteditionapprovedJuly1,2006.PublishedJuly2006.Originallyapproved
in 1989. Last previous edition approved in 2000 as D4061–94(2000). DOI:
10.1520/D4061-94R06.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM AvailablefromU.S.NationalCommitteeoftheCIE(InternationalCommission
Standards volume information, refer to the standard’s Document Summary page on on Illumination), C/o Thomas M. Lemons, TLA-Lighting Consultants, Inc., 7 Pond
the ASTM website. St., Salem, MA 01970.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4061−94(2006)
illumination;forexample,thedirectionoftheroadonwhichor
with respect to which the retroreflector is intended to be
positioned. In testing horizontal road markings the retroreflec-
tor axis is usually the normal to the test surface.
3.2.11 rotation angle, ϵ,n—angle indicating the orientation
ofthespecimenwhenitisrotatedaboutaselectedaxisfixedin
it (for plane specimens, usually the specimen normal); in
retroreflection, the dihedral angle from the half-plane originat-
ingontheretroreflectoraxisandcontainingthepositivepartof
the second axis to the half-plane originating on the retroreflec-
tor axis and containing the datum mark.
NOTE1—Includesobservationangleα,entranceangleβ,viewingangle
3.2.11.1 Discussion—The rotation angle shown in Fig. 3,
ν , co-viewing angle ν , and co-entrance angle β . The retroreflector axis,
a c c
with the datum mark oriented away from the source, is 0°.
illumination axis, and observation axis all lie in the same plane.
3.2.12 source, n—an object that produces light or other
FIG. 1Diagram Illustrating Geometry for Measurement of Hori-
zontal Coatings Specimens
radiant flux.
3.2.13 specific luminance—see coefficient of retroreflected
luminance.
3.2.14 viewing angle, ν—the angle between the observation
axis and the retroreflector axis.
3.2.14.1 Discussion—In testing road markings specimens,
the retroreflector axis is usually the normal to the test surface
(see definition of retroreflector axis).
3.3 Definitions of Terms Specific to This Standard:
3.3.1 co-entrance angle, β,n—the complement of the
c
entrance angle (90°− β).
3.3.1.1 Discussion—On a typical test specimen, this is the
angle from the plane surface of the material to the observation
axis.
FIG. 2 Illustration of Typical Rate of Change of Retroreflectance
Versus Observation Angle for Horizontal Retroreflective Material
3.3.2 co-viewing angle, ν,n—the complement of the view-
c
Measured at 86° Entrance Angle
ing angle (90°− η).
4. Summary of Test Method
3.2.6 observation angle, n—angle between the axes of the
4.1 This test method involves the use of a light-projector
incident beam and the observed (reflected) beam, ( in retrore-
source, a photoreceptor, a specimen holder, and a receptor-
flection, α, between the illumination axis and the observation
source support, all arranged with approximately 15-m separa-
axis).
tion between the specimen holder and receptor-source support
3.2.6.1 Discussion—The observation angle is always posi-
in a suitable darkened area. The observation angle is generally
tive and in the context of retroreflection is restricted to small
small (0.2 to 2.0°) and the entrance angle approaches 90° (the
acute angles.
light is near the grazing angle).
3.2.7 observation axis, n—in retroreflection, a line from the
effective center of the receiver aperture to the retroreflector 4.2 The general procedure is to determine the ratio of the
center. retroreflected light from the test surface to the incident light on
the test surface. From these measurements, the photometric
3.2.8 receiver, n—the portion of a photometric instrument
quantity, specific luminance is calculated.
that receives the viewing beam from the specimen, including a
collector such as an integrating sphere, if used, often the
5. Significance and Use
monochromator or spectral filters, the detector, and associated
5.1 The quantity coefficient of retroreflected luminance is a
optics and electronics.
measure of the reflected luminance in the direction of the
3.2.9 retroreflection, n—reflection in which the reflected
observer.Thisisthelightreturnedbytheretroreflectivesurface
rays are preferentially returned in directions close to the
totheobserverfromthesource,whichinpracticeisthevehicle
opposite of the direction of the incident rays, this property
headlamp.
being maintained over wide variations of the direction of the
B
5.2 This test method may be used as a measure of the
incident rays. [CIE]
nighttime performance of horizontally applied surfacing mate-
3.2.10 retroreflector axis, n—a designated line segment
rials used on highway surfaces for lane markings and other
from the retroreflector center that is used to describe the
traffic control purposes.
angular position of the retroreflector.
3.2.10.1 Discussion—Thedirectionoftheretroreflectoraxis 5.3 Since this test method is a laboratory procedure, test
is usually chosen centrally among the intended directions of specimensmustbepreparedsothattheycanbemountedonthe
D4061−94(2006)
FIG. 3 Arrangement of Test Apparatus
specimen holder. Specimens measured by this laboratory 6.1.3 Illuminated Area—The illumination at the specimen
method may be used as transfer standards for the calibration of produced by the projector shall be such that only the test
portable instrumentation. surface and a minimum of the background is illuminated. This
is commonly accomplished by placing a restrictive aperture in
5.4 Specimen selection and preparation may significantly
the projector slide port.
influence the results of this test method.
6.1.4 Source Stability—The source shall be regulated such
that the illumination at the test surface does not change by
6. Apparatus
more than 61% for the duration of the test.
6.1 Light Source, projector type, meeting the following
6.1.5 Illumination Uniformity—The illumination produced
requirements:
on the specimen surface shall be uniform within 65% of the
6.1.1 Color Temperature—The projection lamp together
average illuminance normal to the source at the test distance.
with the projection optics shall be operated so that they
6.2 Photoreceptor, meeting the following requirements:
illuminate the test specimen with the spectral energy distribu-
5 6.2.1 Sensitivity—The photoreceptor shall have sufficient
tion of the 1931 CIE Standard Source A (a correlated color
sensitivity and range so that readings of both the incident
temperature of 2856 K). A method for determining correlated
illuminance and the retroreflected light at the observation
color temperature is contained in Annex A3 of Practice E809.
position can be measured with a resolution of at least 1 part in
6.1.2 Exit Aperture—The source exit aperture shall be 43
50 on the readout scale.
mm maximum diameter. This corresponds to 10 min of arc
6.2.2 Spectral Response—The spectral response of the pho-
angular aperture at 15 m test distance. In practice, it is
toreceptor shall match that of the 1931 CIE Standard Photopic
convenient to provide the projection with a non-silvered right
Observer. See Annex A1 of Practice E809.
angle prism so that the external physical size of the exit
6.2.3 Stability—The receptor response shall not vary more
aperture is small, allowing its close proximity to the entrance
than 61% for the duration of the test.
aperture of the photoreceptor.
A slide with a 3- by 15-mm opening has been found satisfactory.
4 7
Acommercial slide projector with 7-in. F-3.5 lens and with the heat absorbing Commercially available instruments commonly referred to as telephotometers
filter removed has been found satisfactory as a light source. Such a projector must have been found satisfactory for this purpose.
be run at reduced voltage to achieve the required color temperature and to provide The 1931 CIE Standard Photopic Observer is identical to the y-bar function of
adequate lamp stability. the 1931 CIE Standard Colorimetric Observer, which is tabulated in Practice E308,
See Practice E308, Table3. Table1.
D4061−94(2006)
6.2.4 Linearity—The linearity of the photometric scale over 6.3.3 Leading Edge Reflections—The specimen holder must
the range of readings to be taken shall be within 61%. be provided with a means of eliminating reflections from the
Correction factors may be used to ensure linear response. A leading edge of the specimen, and the holder itself must be
methodfordetermininglinearityiscontainedinPracticeE809, non-reflective.
Annex A2. 6.3.4 Incident Light Measurement Provision—It is desirable
6.2.5 Field of View—The field of view shall be limited by that the specimen holder be such that the photoreceptor can
use of light baffles or a field aperture on the instrument so that easily be substituted for the specimen, which is required when
the entire test specimen is fully within the field of view yet as incident light measurements are taken.
much stray light is rejected as is practical.Abackground light
6.4 Receptor-Source Support—A device that adequately
levellessthan5%ofsmallest m reading(see8.6)isdesirable.
supportsandseparatesthephotoreceptorfromthesourceatthe
Whenbackgroundlevelsaregreaterthan5%,carefulattention
observation position. The required accuracy of separation of
must be given to noise levels.
the source exit aperture from the photoreceptor entrance
6.2.5.1 In this test, the receptor’s field of view must always
aperture is dependent on the properties of the test specimen.
be larger than the projected area of the test specimen.
For most horizontal surfacing materials, the divergence pat-
6.2.6 Entrance Aperture—The photoreceptor shall be pro-
terns are gradual and a positioning accuracy of 61mm(or
vided with an entrance aperture of 43 mm maximum diameter.
60.5% of the resolution) at 15 m test distance is adequate.A
This is equivalent to 10 min angular aperture at 15 m. The
common method of fixing this distance is to provide a bar with
physical size of the entrance aperture must be small so that the
holesmachinedinitatseparationscorrespondingtothedesired
photoreceptor may be positioned physically close to the source
observation angles. In this method, the minimum practical
exit aperture.
observation angle is about 0.2°.
6.3 Specimen Holder—The specimen holder, commonly
6.5 Photometric Site—Sufficient space is required so that
custom built to fit the desired specimen size and shape, must
the projector source and test surface can be separated by about
meet the following requirements (see Fig. 4 and Fig. 5).
15 m. This facility must be such that stray light does not
6.3.1 Angular Accuracy—The test surface must be position-
appreciably affect the test results. Flat black paint, black
ablesothattheentranceangleisaccuratetowithin0.5%ofits
curtains,blacktape,andothermeansshallbeusedtoeliminate
complement (that is, for 86° entrance angle, the angle must be
unwanted light and stray reflections.
accurateto0.005×4°=0.02°).Thi
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