ASTM D4061-94(2000)
(Test Method)Standard Test Method for Retroreflectance of Horizontal Coatings
Standard Test Method for Retroreflectance of Horizontal Coatings
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 Fig. 1).
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 Fig. 2.
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 This standard does not purport to address all of the safety problems, 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: D 4061 – 94 (Reapproved 2000)
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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method describes the instrumental measure-
ment 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 deter-
mined and specified by the user of this test method. Likewise,
theusermustspecifytheobservationandentranceanglestobe
used (see Fig. 1).
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
NOTE 1—Includesobservationangle a,entranceangle b,viewingangle
angle range from 0.2 to 0.5°. This is illustrated in Fig. 2.
n ,co-viewingangle n ,andco-entranceangle b .Theretroreflectoraxis,
a c c
1.4 This test method is a laboratory test and requires a
illumination axis, and observation axis all lie in the same plane.
facilitythatcanbedarkenedsufficientlysothatstraylightdoes FIG. 1 Diagram Illustrating Geometry for Measurement of
Horizontal Coatings Specimens
not affect the test results. This facility must be capable of
housing the required 15-m test distance.
3. Terminology
1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3.1 ThetermsanddefinitionsinTerminologyE284applyto
responsibility of the user of this standard to establish appro-
this test method.
priate safety and health practices and determine the applica-
3.2 Definitions:
bility of regulatory limitations prior to use.
3.2.1 coeffıcient of retroreflected luminance, R , n—ratioof
L
the luminance, L, of a projected surface to the normal illumi-
2. Referenced Documents
nance, E , at the surface on a plane normal to the incident
'
2.1 ASTM Standards:
light, expressed in candelas per square metre per lux
−2 −1
E284 Terminology of Appearance
(cd·m ·lx ).
E308 Praactice for Computing the Colors of Objects by
Using the CIE System
E808 Practice for Describing Retroreflection
E809 Practice for Measuring Photometric Characteristics
of Retroreflectors
2.2 CIE Publication:
No. 54 Retroreflection Definition and Measurement
This test method is under the jurisdiction of ASTM Committee E12 on Color
and Appearance and is the direct responsibility of Subcommittee E12.10 on
Retroreflection.
Current edition approved Feb. 15, 1994. Published April 1994. Originally
published as D4061–89. Last previous edition D4061–93b.
Annual Book of ASTM Standards, Vol 06.01.
FIG. 2 Illustration of Typical Rate of Change of Retroreflectance
Available from U.S. National Committee, CIE (International Commission on
Versus Observation Angle for Horizontal Retroreflective Material
Illumination) Publications Office, TLA Lighting Consultants, 72 Loring Ave.,
Salem, MA 01970. Measured at 86° Entrance Angle
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 4061 – 94 (2000)
R 5 ~L/E ! (1) it (for plane specimens, usually the specimen normal); in
L '
retroreflection, the dihedral angle from the half-plane originat-
ingontheretroreflectoraxisandcontainingthepositivepartof
3.2.2 datum mark, n—in retroreflection,anindicationonthe
the second axis to the half-plane originating on the retroreflec-
retroreflector that is used to define the orientation of the
tor axis and containing the datum mark.
retroreflector with respect to rotation about the retroreflector
3.2.11.1 Discussion—The rotation angle shown in Fig. 3,
axis.
with the datum mark oriented away from the source, is 0°.
3.2.2.1 Discussion—The datum mark must not lie on the
3.2.12 source, n—an object that produces light or other
retroreflector axis.
radiant flux.
3.2.3 entrance angle, b, n—in retroreflection, angle be-
3.2.13 specific luminance—see coefficient of retroreflected
tween the illumination axis and the retroreflector axis.
luminance.
3.2.3.1 Discussion—For plane retroreflective surfaces, the
3.2.14 viewing angle, n—the angle between the observation
entrance angle is no larger than 90°.
axis and the retroreflector axis.
3.2.3.2 Discussion—The entrance angle may be divided
3.2.14.1 Discussion—In testing road markings specimens,
into components b and b . This is described in Practice
1 2
the retroreflector axis is usually the normal to the test surface
E808. In this test method only the component b is used.
(see definition of retroreflector axis).
Therefore, where only the entrance angle b is specified the
3.3 Definitions of Terms Specific to This Standard:
convention used is b =0 and b = b.
2 1
3.3.1 co-entrance angle, b , n—the complement of the
c
3.2.4 illumination axis, n— in retroreflection, a line from
entrance angle (90°− b).
the effective center of the source aperture to the retroreflector
3.3.1.1 Discussion—On a typical test specimen, this is the
center.
angle from the plane surface of the material to the observation
3.2.5 normal illuminance, E — the illuminance on a ret-
'
axis.
roreflective surface measured in the plane that passes through
3.3.2 co-viewing angle, n , n—the complement of the view-
c
theretroreflectorcenterandisperpendiculartotheillumination
−2
ing angle (90°− h).
axis; measured in lux (lumens·m ).
3.2.6 observation angle, n—angle between the axes of the
4. Summary of Test Method
incident beam and the observed (reflected) beam, ( in retrore-
flection, a, between the illumination axis and the observation 4.1 This test method involves the use of a light-projector
axis). source, a photoreceptor, a specimen holder, and a receptor-
source support, all arranged with approximately 15-m separa-
3.2.6.1 Discussion—The observation angle is always posi-
tive and in the context of retroreflection is restricted to small tion between the specimen holder and receptor-source support
in a suitable darkened area. The observation angle is generally
acute angles.
small (0.2 to 2.0°) and the entrance angle approaches 90° (the
3.2.7 observation axis, n— in retroreflection,alinefromthe
light is near the grazing angle).
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
3.2.8 receiver, n—the portion of a photometric instrument
the test surface. From these measurements, the photometric
that receives the viewing beam from the specimen, including a
quantity, specific luminance is calculated.
collector such as an integrating sphere, if used, often the
monochromator or spectral filters, the detector, and associated
5. Significance and Use
optics and electronics.
3.2.9 retroreflection, n—reflection in which the reflected
5.1 The quantity coefficient of retroreflected luminance is a
rays are preferentially returned in directions close to the
measure of the reflected luminance in the direction of the
opposite of the direction of the incident rays, this property
observer.Thisisthelightreturnedbytheretroreflectivesurface
being maintained over wide variations of the direction of the
totheobserverfromthesource,whichinpracticeisthevehicle
B
incident rays. [CIE]
headlamp.
3.2.10 retroreflector axis, n—a designated line segment
5.2 This test method may be used as a measure of the
from the retroreflector center that is used to describe the
nighttime performance of horizontally applied surfacing mate-
angular position of the retroreflector.
rials used on highway surfaces for lane markings and other
traffic control purposes.
3.2.10.1 Discussion—Thedirectionoftheretroreflectoraxis
is usually chosen centrally among the intended directions of 5.3 Since this test method is a laboratory procedure, test
illumination;forexample,thedirectionoftheroadonwhichor
specimensmustbepreparedsothattheycanbemountedonthe
with respect to which the retroreflector is intended to be specimen holder. Specimens measured by this laboratory
positioned. In testing horizontal road markings the retroreflec-
method may be used as transfer standards for the calibration of
tor axis is usually the normal to the test surface. portable instrumentation.
3.2.11 rotation angle, e, n—angle indicating the orientation 5.4 Specimen selection and preparation may significantly
influence the results of this test method.
ofthespecimenwhenitisrotatedaboutaselectedaxisfixedin
D 4061 – 94 (2000)
FIG. 3 Arrangement of Test Apparatus
6. Apparatus 6.1.5 Illumination Uniformity—The illumination produced
on the specimen surface shall be uniform within 65% of the
6.1 Light Source, projector type, meeting the following
4 average illuminance normal to the source at the test distance.
requirements:
6.2 Photoreceptor, meeting the following requirements:
6.1.1 Color Temperature—The projection lamp together
6.2.1 Sensitivity—The photoreceptor shall have sufficient
with the projection optics shall be operated so that they
sensitivity and range so that readings of both the incident
illuminate the test specimen with the spectral energy distribu-
5 illuminance and the retroreflected light at the observation
tion of the 1931 CIE Standard Source A (a correlated color
position can be measured with a resolution of at least 1 part in
temperature of 2856 K). A method for determining correlated
50 on the readout scale.
color temperature is contained inAnnexA3 of Practice E809.
6.2.2 Spectral Response—The spectral response of the pho-
6.1.2 Exit Aperture—The source exit aperture shall be 43
toreceptor shall match that of the 1931 CIE Standard Photopic
mm maximum diameter. This corresponds to 10 min of arc
Observer. See Annex A1 of Practice E809.
angular aperture at 15 m test distance. In practice, it is
6.2.3 Stability—The receptor response shall not vary more
convenient to provide the projection with a non-silvered right
than 61% for the duration of the test.
angle prism so that the external physical size of the exit
6.2.4 Linearity—The linearity of the photometric scale over
aperture is small, allowing its close proximity to the entrance
the range of readings to be taken shall be within 61%.
aperture of the photoreceptor.
Correction factors may be used to ensure linear response. A
6.1.3 Illuminated Area—The illumination at the specimen
method for determining linearity is contained in Practice
produced by the projector shall be such that only the test
E809, Annex A2.
surface and a minimum of the background is illuminated. This
6.2.5 Field of View—The field of view shall be limited by
is commonly accomplished by placing a restrictive aperture in
use of light baffles or a field aperture on the instrument so that
the projector slide port.
the entire test specimen is fully within the field of view yet as
6.1.4 Source Stability—The source shall be regulated such
much stray light is rejected as is practical.Abackground light
that the illumination at the test surface does not change by
level less than 5% of smallest m reading (see section 7.6 ) is
more than6 1% for the duration of the test. 1
Acommercial slide projector with 7-in. F-3.5 lens and with the heat absorbing
filter removed has been found satisfactory as a light source. Such a projector must Commercially available instruments commonly referred to as telephotometers
be run at reduced voltage to achieve the required color temperature and to provide have been found satisfactory for this purpose.
adequate lamp stability. The 1931 CIE Standard Photopic Observer is identical to the y-bar function of
See Practice E308, Table3. the 1931 CIE Standard Colorimetric Observer, which is tabulated in Practice E308,
A slide with a 3-mm by 15-mm opening has been found satisfactory. Table1.
D 4061 – 94 (2000)
desirable. When background levels are greater than 5%, the source exit aperture from the photoreceptor entrance
careful attention must be given to noise levels. aperture is dependent on the properties of the test specimen.
6.2.5.1 In this test, the receptor’s field of view must always For most horizontal surfacing materials, the divergence pat-
be larger than the projected area of the test specimen. terns are gradual and a positioning accuracy of 61mm(or
6.2.6 Entrance Aperture—The photoreceptor shall be pro- 60.5% of the resolution) at 15 m test distance is adequate.A
vided with an entrance aperture of 43 mm maximum diameter. common method of fixing this distance is to provide a bar with
This is equivalent to 10 min angular aperture at 15 m. The holesmachinedinitatseparationscorrespondingtothedesired
physical size of the entrance aperture must be small so that the observation angles. In this method, the minimum practical
photoreceptor may be positioned physically close to the source observation angle is about 0.2°.
exit aperture. 6.5 Photometric Site—Sufficient space is required so that
6.3 Specimen Holder—The specimen holder, commonly the projector source and test surface can be separated by about
custom built to fit the desired specimen size and shape, must 15 m. This facility must be such that stray light does not
meet the following requirements (see Fig. 4 and Fig. 5). appreciably affect the test results. Flat black paint, black
6.3.1 Angular Accuracy—Thetestsurfacemustbeposition- curtains,blacktape,andothermeansshallbeusedtoeliminate
ablesothattheentranceangleisaccuratetowithin0.5%ofits unwanted light and stray reflections.
complement (that is, for 86° entrance angle, the angle must be
accurate to 0.005 34°=0.02°). This accuracy may be ob-
7. Test Specimens
tainedbyprovidinganopticalmeanstoalignthetestsurfaceto
7.1 Thepreparationoftestspecimensisnotdescribedinthis
90° entrance angle and then adjusting to the desired entrance
test method. For example, the user of the test methodmust
angle. (See Figs. 6-9 for examples of angular setting devices.)
describe a method of application of glass beads to a painted
6.3.2 Entrance Angle Axis—A means must be provided to
surface.
change the entrance angle such that the axis of rotation is
7.2 To obtain a flat surface, the test material is usually
contained in the plane of the test surface if several entrance
adhered to an aluminum backing or other suitable substrate so
angles are to be used.
that the material lies flat for testing.
6.3.3 Leading Edge Reflections—Thespecimenholdermust
7.3 Typically, the area of the test specimen may be 100
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