ASTM E810-03(2008)
(Test Method)Standard Test Method for Coefficient of Retroreflection of Retroreflective Sheeting Utilizing the Coplanar Geometry
Standard Test Method for Coefficient of Retroreflection of Retroreflective Sheeting Utilizing the Coplanar Geometry
SIGNIFICANCE AND USE
Measurements made by this test method are related to visual observations of retroreflective sheeting as seen by the human eye when illuminated by tungsten-filament light sources such as a motor vehicle headlamp.
The values determined relate to the visual effects for a given geometric configuration as specified by the user of the test method. This test method has been found useful for tests at observation angles between 0.1 and 2.0° (observation angles between 0.1° and 0.2° may be achieved by careful design of source and receiver aperture configuration), and at entrance angles up to 60°. It has been used to determine coefficient of retroreflection values as low as 0.1 cd·lx−1· m−2, but for values less than 1 cd·lx−1· m−2 special attention must be given to the responsivity of the receiver and to the elimination of very small amounts of stray light.
SCOPE
1.1 This test method describes an instrument measurement of the retroreflective performance of retroreflective sheeting.
1.2 The user of this test method must specify the entrance and observation angles to be used, and may specify the rotation angles.
1.3 This test method is intended as a laboratory test and requires a facility that can be darkened sufficiently so that stray light does not affect the test results. The testing apparatus must be able to achieve the coplanar geometry.
1.4 Portable and bench retroreflection measuring equipment may be used to determine RA values provided the geometry and appropriate substitution standard reference panels, measured in accordance with this test method, are utilized. In this case the methods of Procedure B in Practice E 809 apply. Additional information on the use of portable retroreflectometers may be found in Test Method E 1709.
1.5 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:E810 −03(Reapproved2008)
Standard Test Method for
Coefficient of Retroreflection of Retroreflective Sheeting
Utilizing the Coplanar Geometry
This standard is issued under the fixed designation E810; 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 an instrument measurement
E1709Test Method for Measurement of Retroreflective
of the retroreflective performance of retroreflective sheeting.
Signs Using a Portable Retroreflectometer at a 0.2 Degree
1.2 The user of this test method must specify the entrance
Observation Angle
andobservationanglestobeused,andmayspecifytherotation
2.2 Other Document:
angles.
CIE Publication No 54 Retroreflection—Definition and
1.3 This test method is intended as a laboratory test and Measurement
requiresafacilitythatcanbedarkenedsufficientlysothatstray
3. Terminology
light does not affect the test results.The testing apparatus must
be able to achieve the coplanar geometry.
3.1 The terms and definitions in Terminology E284 and
Practice E808 apply to this test method.
1.4 Portable and bench retroreflection measuring equipment
maybeusedtodetermine R valuesprovidedthegeometryand
A 3.2 Definitions:
appropriatesubstitutionstandardreferencepanels,measuredin
3.2.1 coeffıcient of retroreflection, R —of a plane retrore-
A
accordance with this test method, are utilized. In this case the
flecting surface, the ratio of the coefficient of luminous
methods of Procedure B in Practice E809 apply. Additional
intensity(R )tothearea(A),expressedincandelasperluxper
I
−1 −2
information on the use of portable retroreflectometers may be
square metre (cd·lx ·m ). R = R/A.
A I
found in Test Method E1709.
3.2.1.1 Discussion—The equivalent inch–pound units for
coefficient of retroreflection are candelas per foot-candle per
1.5 This standard does not purport to address all of the
−1 −2
square foot (cd·fc ·ft ). The SI and inch pound units are
safety concerns, if any, associated with its use. It is the
numerically equal, because the units of R reduce to 1/sr. An
responsibility of the user of this standard to establish appro-
A
equivalenttermusedforcoefficientofretroreflectionisspecific
priate safety and health practices and determine the applica-
intensity per unit area, with symbol SIAor the CIE symbol R'.
bility of regulatory limitations prior to use.
Thetermcoefficientofretroreflectionandthesymbol R along
A
with the SI units of candelas per lux per square meter
2. Referenced Documents
−1 −2
2 (cd·lx ·m ) are recommended by ASTM.
2.1 ASTM Standards:
3.2.1.2 Discussion—R is a useful engineering quantity for
A
E284Terminology of Appearance
determining the photometric performance of such retroreflec-
E308PracticeforComputingtheColorsofObjectsbyUsing
tive surfaces as highway delineators or warning devices. R
A
the CIE System
may also be used to determine the minimum area of retrore-
E691Practice for Conducting an Interlaboratory Study to
flective sheeting necessary for a desired level of photometric
Determine the Precision of a Test Method
performance. R has been used extensively in the specification
A
E808Practice for Describing Retroreflection
of retroreflective sheeting.
3.2.2 coplanar geometry, n—retroreflection geometry in
whichtheretroreflectoraxis,illuminationaxis,andobservation
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
axis lie in one plane.
Retroreflection.
3.2.2.1 Discussion—In the coplanar geometry: the second
Current edition approved Feb. 1, 2008. Published February 2008. Originally
entrance angle component, β , is equal to 0°; presentation
approved in 1981. Last previous edition approved in 2003 as E810–03. DOI: 2
10.1520/E0810-03R08.
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, http://www.cie-usnc.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E810−03(2008)
angle, γ, is equal to either 0° or 180°; orientation angle, ω,is illumination;forexample,thedirectionoftheroadonwhichor
s
equal to either the rotation angle, ε,orto ε + 180° or ε − 180°. with respect to which the retroreflector is intended to be
positioned. The retroreflector axis usually coincides with the
3.2.3 datum axis, n—adesignatedhalf-linefromtheretrore-
axis of symmetry of the retroreflector. For retroreflective
flector center perpendicular to the retroreflector axis.
sheetingthenormaltothesurfaceischosenastheretroreflector
3.2.4 datum mark, n—anindicationontheretroreflector,off
axis.
the retroreflector axis, that establishes the direction of the
3.2.16 retroreflector center, n—the point on or near a ret-
datum axis.
roreflector that is designated to be the location of the device.
3.2.5 entrance angle, β,n—the angle between the illumina-
3.2.17 rotation angle,ε,n—theangleinaplaneperpendicu-
tion axis and the retroreflector axis.
lar to the retroreflector axis from the observation half-plane to
3.2.5.1 Discussion—The entrance angle is usually no larger
the datum axis, measured counterclockwise from a viewpoint
than 90°, but for completeness its full range is defined as 0° ≤
on the retroreflector axis.
β≤180°.IntheCIE(goniometersystem)βisresolvedintotwo
3.2.17.1 Discussion—Range:−180° <ε≤ 180°. The defini-
componentsβ andβ .Sincebydefinitionβisalwayspositive,
1 2
tion is applicable when entrance angle and viewing angle are
the common practice of referring to the small entrance angles
less than 90°. More generally, rotation angle is the angle from
that direct specular reflections away from the photoreceptor as
the positive part of second axis to the datum axis, measured
anegativevalueisdeprecatedbyASTM.Therecommendation
counterclockwise from a viewpoint on the retroreflector axis.
is to designate such negative values as belonging to β .
3.2.17.2 Discussion—Rotation of the sample about the ret-
3.2.6 goniometer, n—an instrument for measuring or setting
roreflector axis while the source and receiver remain fixed in
angles.
space changes the rotation angle (ε) and the orientation angle
(ω ) equally.
3.2.7 illumination axis, n—thehalf-linefromtheretroreflec-
s
tor center through the source point.
3.2.18 rotationally uniform, adj—having substantially con-
stant R , when rotated about the retroreflector axis, while the
3.2.8 observation angle, α,n—the angle between the illu-
A
source, receiver, retroreflector center and retroreflector axis all
mination axis and the observation axis.
remain in a fixed spatial relation.
3.2.8.1 Discussion—The observation angle is never nega-
3.2.18.1 Discussion—The degree of rotational uniformity
tive and is almost always less than 10° and usually no more
can be specified numerically.
than 2°. The full range is defined as 0°≤α < 180°.
3.2.19 source, n—an object that produces light or other
3.2.9 observation axis, n—the half-line from the retroreflec-
radiant flux.
tor center through the observation point.
3.2.10 receiver, n— the portion of a photometric instrument
4. Summary of Test Method
that receives the viewing beam from the specimen, including a
4.1 This test method involves the use of a light projector
collector such as an integrating sphere, if used, often the
source,areceiver,adevicetopositionthereceiverwithrespect
monochromator or spectral filters, the detector, and associated
to the source and a test specimen holder in a suitable darkened
optics and electronics.
area.Thespecimenholderisseparatedfromthelightsourceby
3.2.11 retroreflection, n—reflection in which the reflected
15 m.
rays are preferentially returned in directions close to the
opposite of the direction of the incident rays, this property
4.2 Thegeneralprocedureinvolvedistodeterminetheratio
being maintained over wide variations of the direction of the of the light retroreflected from the test surface to that incident
B
incident rays. [CIE]
on the test surface.
3.2.12 retroreflective material, n—a material that has a thin
4.3 The photometric quantity, coefficient of retroreflection,
continuous layer of small retroreflective elements on or very
is calculated from these measurements.
near its exposed surface (for example, retroreflective sheeting,
retroreflective fabrics, transfer films, beaded paint, highway
5. Significance and Use
surface signs, or pavement striping).
5.1 Measurements made by this test method are related to
3.2.13 retroreflective sheeting—a retroreflective material
visual observations of retroreflective sheeting as seen by the
preassembled as a thin film ready for use.
humaneyewhenilluminatedbytungsten-filamentlightsources
such as a motor vehicle headlamp.
3.2.14 retroreflector, n—a reflecting surface or device from
which, when directionally irradiated, the reflected rays are
5.2 The values determined relate to the visual effects for a
preferentiallyreturnedindirectionsclosetotheoppositeofthe
given geometric configuration as specified by the user of the
direction of the incident rays, this property being maintained
testmethod.Thistestmethodhasbeenfoundusefulfortestsat
over wide variations of the direction of the incident rays. [CIE,
observation angles between 0.1 and 2.0° (observation angles
B
1982]
between 0.1° and 0.2° may be achieved by careful design of
3.2.15 retroreflector axis, n—adesignatedhalf-linefromthe
source and receiver aperture configuration), and at entrance
retroreflector center. angles up to 60°. It has been used to determine coefficient of
−1 −2
3.2.15.1 Discussion—Thedirectionoftheretroreflectoraxis retroreflection values as low as 0.1 cd·lx ·m , but for values
−1 −2
is usually chosen centrally among the intended directions of less than 1 cd·lx ·m special attention must be given to the
E810−03(2008)
responsivityofthereceiverandtotheeliminationofverysmall 6.2.5 Thestabilityofthereceivershallbesuchthatreadings
amounts of stray light. from a constant source do not vary any more than 1% for the
duration of the test.
6. Apparatus 6.2.6 The field of view shall be limited by use of light
baffles or a field aperture on the instrument so that the entire
6.1 Light Source—The light source shall be of the projector
testsampleisfullywithinthefieldofview,rejectingstraylight
typeandshallmeetthefollowingrequirements(anilluminance
asmuchaspractical.Abackgroundlightlevel m lessthan5%
b
at the 15 m specimen distance of about 10 lx is commonly
of the smallest m reading is acceptable.
available within these restrictions):
6.2.7 The receiver aperture shall be a standard circular
6.1.1 The spectral energy distribution of the source shall be
aperture as defined in Practice E809. For measurements at
proportional to CIE standard Source A (a correlated color
observation angles (α) of 0.2°≤α≤ 2.0°, the receiver shall be
temperature of 2856 K, see Practice E308). The projection
provided with an entrance aperture 26 mm (62 mm) in
lamp together with the projection optics shall be operated such
diameter.Thiscorrespondsto0.1°angularapertureat15mtest
that it illuminates the test specimen with this spectral power
distance. For measurements at observation angles (α) of 0.1° ≤
distribution.
α < 0.2°, the receiver shall be provided with an entrance
6.1.2 An unpolarizing light source shall be used.
aperture 13 mm (61 mm) in diameter. This corresponds to a
6.1.3 The source aperture shall be a standard circular
0.05° angular aperture at 15 m test distance. The size of the
aperture as defined in Practice E809. For measurements at
entrance aperture stop must be small so that the receiver may
observation angles (α) of 0.2°≤α≤ 2.0°, the exit aperture of
be positioned physically close to the source exit aperture
the source shall be uniformly radiant, circular and 26 mm (62
without shadowing any of the illuminating light beam.
mm) in diameter. This corresponds to 0.1° angular aperture at
6.3 Test Specimen Goniometer (Test Specimen Holder)—
15mtestdistance.Formeasurementsatobservationangles(α)
Thespecimenholdermustholda200mmsquarespecimenand
of 0.1°≤α < 0.2°, the exit aperture of the source shall be
meet the following requirements (see Fig. 1):
uniformly radiant, circular and 13 mm (61 mm) in diameter.
6.3.1 A means must be provided to rotate the specimen on
This corresponds to 0.05° angular aperture at 15 m test
anaxiscontainedintheplaneofthespecimensurfaceifseveral
distance.
entrance angles are to be used.
6.1.4 The illumination at the sample produced by the
6.3.1.1 The entrance angle component β is used to set the
projector shall be such that the test specimen and only a
goniometer when no specific component is specified (see
minimum of the background is illuminated. This is commonly
Practice E808).
accomplished by placing a restrictive aperture in the projector
6.3.2 The specimen surface must be positionable so that the
slide port.
entrance angle is accurate to within 0.5% of its complement
6.1.5 The source shall be regulated such that the illumi-
(that is, for a 30° entrance angle this angle must be accurately
nance at the test surface does not change by more than 61%
set to 6 0.005 × 60°= 60.3°).This is obtainable by providing
for the duration of the test.
an accurate optical means to align the test surface to the “0
6.1.6 The illuminance produced on the sample surface shall
degree” entrance angle and then adjusting the angular setting
be uniform within 65% of the average illuminance normal to
(within the required tolerance).
the source at the distance of 15 m.
6.2 Receiver—The receiver shall meet the requirements that
−1 −2
follow. (In this test, for 10 lx incident upon a 1 cd·lx ·m
retroreflective sheeting test specimen with area of 0.04 m , the
incident normal illuminance at the receiver will be about
−3
1.8×10 lx).
6.2.1 The responsivity and range of the receiver shall be
sufficient so that readings of both the incident normal illumi-
nance (at the specimen) and the retroreflected light at the
observation position can be measured with a resolution of at
least 1 part in 50 on the readout scale.
6.2.2 The spectral responsivity of the receiver shall match
that of the 1931 CIE Standard Photopic Observer (see Annex
A1 of Practice E809).
6.2.3 The
...
This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
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 version
of the standard as published by ASTM is to be considered the official document.
Designation:E810–01 Designation: E 810 – 03 (Reapproved 2008)
Standard Test Method for
Coefficient of Retroreflection of Retroreflective Sheeting
Utilizing the Coplanar Geometry
This standard is issued under the fixed designation E810; 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 an instrument measurement of the retroreflective performance of retroreflective sheeting.
1.2 The user of this test method must specify the entrance and observation angles to be used, and may specify the rotation
angles.
1.3 This test method is intended as a laboratory test and requires a facility that can be darkened sufficiently so that stray light
does not affect the test results. The testing apparatus must be able to achieve the coplanar geometry.
1.4 Portable and bench retroreflection measuring equipment may be used to determine R values provided the geometry and
A
appropriate substitution standard reference panels, measured in accordance with this test method, are utilized. In this case the
methods of Procedure B in Practice E809 apply.Additional information on the use of portable retroreflectometers may be found
in Test Method E1709.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
E284 Terminology of Appearance
E308 Practice for Computing the Colors of Objects by Using the CIE System
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E808 Practice for Describing Retroreflection
E809 Practice for Measuring Photometric Characteristics of Retroreflectors
E1709 Test Method for Measurement of Retroreflective Signs Using a Portable Retroreflectivemeter Retroreflectometer
2.2 Other Document:
CIE Publication No54 Retroreflection—Definition and Measurement
3. Terminology
3.1 The terms and definitions in Terminology E284 and Practice E808 apply to this test method.
3.2 Definitions:
3.2.1 coeffıcient of retroreflection, R —of a plane retroreflecting surface, the ratio of the coefficient of luminous intensity (R )
A I
−1 −2
to the area ( A), expressed in candelas per lux per square metre (cd·lx ·m ). R = R/A.
A I
3.2.1.1 Discussion—The equivalent inch–pound units for coefficient of retroreflection are candelas per foot-candle per square
−1 −2
foot (cd·fc ·ft ). The SI and inch pound units are numerically equal, because the units of R reduce to 1/sr.An equivalent term
A
usedforcoefficientofretroreflectionisspecificintensityperunitarea,withsymbolSIAortheCIEsymbolR8.Thetermcoefficient
−1 −2
of retroreflection and the symbol R along with the SI units of candelas per lux per square meter (cd·lx ·m ) are recommended
A
by ASTM.
3.2.1.2 Discussion—R is a useful engineering quantity for determining the photometric performance of such retroreflective
A
surfacesashighwaydelineatorsorwarningdevices. R mayalsobeusedtodeterminetheminimumareaofretroreflectivesheeting
A
ThistestmethodisunderthejurisdictionofASTMCommitteeE12onColorandAppearanceandisthedirectresponsibilityofSubcommitteeE12.10onRetroreflection.
Current edition approved June 10, 2001. Published August 2001. Originally published as E810–81. Last previous edition E810–94(2000).
Current edition approved Feb. 1, 2008. Published February 2008. Originally approved in 1981. Last previous edition approved in 2003 as E810–03.
ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatservice@astm.org.For Annual Book of ASTM Standards
, Vol 06.01.volume information, refer to the standard’s Document Summary page on the ASTM website.
Annual Book of ASTM Standards, Vol 14.02.
Available from U.S. National Committee of the CIE (International Commission on Illumination), C/o Thomas M. Lemons, TLA-Lighting Consultants, Inc., 7 Pond St.,
Salem, MA 01970, http://www.cie-usnc.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 810 – 03 (2008)
necessary for a desired level of photometric performance. R has been used extensively in the specification of retroreflective
A
sheeting.
3.2.2 coplanar geometry, n—retroreflection geometry in which the retroreflector axis, illumination axis, and observation axis
lie in one plane.
3.2.2.1 Discussion—In the coplanar geometry: the second entrance angle component, b , is equal to 0°; presentation angle, g,
is equal to either 0° or 180°; orientation angle, v , is equal to either the rotation angle, e,orto e + 180° or e − 180°.
s
3.2.3 datum axis, n—a designated half-line from the retroreflector center perpendicular to the retroreflector axis.
3.2.4 datum mark, n— an indication on the retroreflector, off the retroreflector axis, that establishes the direction of the datum
axis.
3.2.5 entrance angle, b, n—the angle between the illumination axis and the retroreflector axis.
3.2.5.1 Discussion—The entrance angle is usually no larger than 90°, but for completeness its full range is defined as 0°# b
# 180°. In the CIE (goniometer system) b is resolved into two components b and b . Since by definition b is always positive,
1 2
the common practice of referring to the small entrance angles that direct specular reflections away from the photoreceptor as a
negative value is deprecated by ASTM. The recommendation is to designate such negative values as belonging to b .
3.2.6 goniometer, n—an instrument for measuring or setting angles.
3.2.7 illumination axis, n—the half-line from the retroreflector center through the source point.
3.2.8 observation angle, a, n—the angle between the illumination axis and the observation axis.
3.2.8.1 Discussion—The observation angle is never negative and is almost always less than 10° and usually no more than 2°.
The full range is defined as 0°# a < 180°.
3.2.9 observation axis, n—the half-line from the retroreflector center through the observation point.
3.2.10 receiver, n— the portion of a photometric instrument that receives the viewing beam from the specimen, including a
collector such as an integrating sphere, if used, often the monochromator or spectral filters, the detector, and associated optics and
electronics.
3.2.11 retroreflection, n—reflection in which the reflected rays are preferentially returned in directions close to the opposite of
B
the direction of the incident rays, this property being maintained over wide variations of the direction of the incident rays. [CIE]
3.2.12 retroreflective material, n—a material that has a thin continuous layer of small retroreflective elements on or very near
its exposed surface (for example, retroreflective sheeting, retroreflective fabrics, transfer films, beaded paint, highway surface
signs, or pavement striping).
3.2.13 retroreflective sheeting—a retroreflective material preassembled as a thin film ready for use.
3.2.14 retroreflector, n—a reflecting surface or device from which, when directionally irradiated, the reflected rays are
preferentially returned in directions close to the opposite of the direction of the incident rays, this property being maintained over
B
wide variations of the direction of the incident rays. [CIE, 1982]
3.2.15 retroreflector axis, n—a designated half-line from the retroreflector center.
3.2.15.1 Discussion—The direction of the retroreflector axis is usually chosen centrally among the intended directions of
illumination;forexample,thedirectionoftheroadonwhichorwithrespecttowhichtheretroreflectorisintendedtobepositioned.
The retroreflector axis usually coincides with the axis of symmetry of the retroreflector. For retroreflective sheeting the normal to
the surface is chosen as the retroreflector axis.
3.2.16 retroreflector center, n—the point on or near a retroreflector that is designated to be the location of the device.
3.2.17 rotation angle, e, n—the angle in a plane perpendicular to the retroreflector axis from the observation half-plane to the
datum axis, measured counterclockwise from a viewpoint on the retroreflector axis.
3.2.17.1 Discussion— Range:−180° < e# 180°. The definition is applicable when entrance angle and viewing angle are less
than 90°. More generally, rotation angle is the angle from the positive part of second axis to the datum axis, measured
counterclockwise from a viewpoint on the retroreflector axis.
3.2.17.2 Discussion—Rotation of the sample about the retroreflector axis while the source and receiver remain fixed in space
changes the rotation angle (e) and the orientation angle (v ) equally.
s
3.2.18 rotationally uniform, adj—havingsubstantiallyconstantR ,whenrotatedabouttheretroreflectoraxis,whilethesource,
A
receiver, retroreflector center and retroreflector axis all remain in a fixed spatial relation.
3.2.18.1 Discussion—The degree of rotational uniformity can be specified numerically.
3.2.19 source, n—an object that produces light or other radiant flux.
4. Summary of Test Method
4.1 This test method involves the use of a light projector source, a receiver, a device to position the receiver with respect to the
source and a test specimen holder in a suitable darkened area. The specimen holder is separated from the light source by 15 m.
4.2 The general procedure involved is to determine the ratio of the light retroreflected from the test surface to that incident on
the test surface.
4.3 The photometric quantity, coefficient of retroreflection, is calculated from these measurements.
5. Significance and Use
5.1 Measurements made by this test method are related to visual observations of retroreflective sheeting as seen by the human
E 810 – 03 (2008)
eye when illuminated by tungsten-filament light sources such as a motor vehicle headlamp.
5.2 The values determined relate to the visual effects for a given geometric configuration as specified by the user of the test
method. This test method has been found useful for tests at observation angles between 0.1 and 2.0° (observation angles between
0.1° and 0.2° may be achieved by careful design of source and receiver aperture configuration), and at entrance angles up to 60°.
−1 −2 −1
It has been used to determine coefficient of retroreflection values as low as 0.1 cd·lx ·m , but for values less than 1 cd·lx ·
−2
m special attention must be given to the responsivity of the receiver and to the elimination of very small amounts of stray light.
6. Apparatus
6.1 Light Source—The light source shall be of the projector type and shall meet the following requirements (an illuminance at
the 15-m15 m specimen distance of about 10 lx is commonly available within these restrictions):
6.1.1 The spectral energy distribution of the source shall be proportional to CIE standard Source A (a correlated color
temperature of 2856 K, see Practice E308). The projection lamp together with the projection optics shall be operated such that
it illuminates the test specimen with this spectral power distribution.
6.1.2 An unpolarizing light source shall be used.
6.1.3At observation angles between 0.2° and 2.0°, the exit aperture of the source shall be uniformly radiant, circular and 26 mm
(62 mm) in diameter. This corresponds to a 0.1° angular aperture at the 15 m test distance. At observation angles between 0.1°
and 0.2°, the exit aperture of the source shall be uniformly radiant, circular and 13 mm (61 mm) in diameter. This corresponds
to a 0.05° angular aperture at the 15 m test distance.
6.1.3 The source aperture shall be a standard circular aperture as defined in Practice E809. For measurements at observation
angles(a)of0.2°# a#2.0°,theexitapertureofthesourceshallbeuniformlyradiant,circularand26mm(62mm)indiameter.
This corresponds to 0.1° angular aperture at 15 m test distance. For measurements at observation angles (a) of 0.1°# a < 0.2°,
the exit aperture of the source shall be uniformly radiant, circular and 13 mm (61 mm) in diameter. This corresponds to 0.05°
angular aperture at 15 m test distance.
6.1.4 The illumination at the sample produced by the projector shall be such that the test specimen and only a minimum of the
background is illuminated. This is commonly accomplished by placing a restrictive aperture in the projector slide port.
6.1.5 The source shall be regulated such that the illuminance at the test surface does not change by more than 61% for the
duration of the test.
6.1.6 The illuminance produced on the sample surface shall be uniform within 65% of the average illuminance normal to the
source at the distance of 15 m.
−1 −2
6.2 Receiver—The receiver shall meet the requirements that follow. (In this test, for 10 lx incident upon a 1 cd·lx ·m
retroreflective sheeting test specimen with area of 0.04 m , the incident normal illuminance at the receiver will be about 1.8 310
−3lx).
6.2.1 The responsivity and range of the receiver shall be sufficient so that readings of both the incident normal illuminance (at
the specimen) and the retroreflected light at the observation position can be measured with a resolution of at least 1 part in 50 on
the readout scale.
6.2.2 The spectral responsivity of the receiver shall match that of the 1931 CIE Standard Photopic Observer (seeAnnexA1 of
Practice E809).
6.2.3 The receiver shall be insensitive to the polarization of light.
6.2.4 Thelinearityofthephotometricscaleovertherangeofreadingstobetakenshallbewithin 61%.Correctionfactorsmay
be used to ensure a linear response. Linearity verification tests must be made utilizing the entire receiver readout device including
the detector, load, range selection system and readout display device.
6.2.5 The stability of the receiver shall be such that readings from a constant source do not vary any more than 1% for the
duration of the test.
6.2.6 The field of view shall be limited by use of light baffles or a field aperture on the instrument so that the entire test sample
isfullywithinthefieldofview,rejectingstraylightasmuchaspractical.Abackgroundlightlevel m lessthan5%ofthesmallest
b
m reading is acceptable.
6.2.7 The receiver aperture shall be a standard circular aperture as defined in Practice E809. For measurements at observation
anglesbetween(a)of0.2°an
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