ASTM E811-09(2020)e1

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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Designation:E811 −09 (Reapproved 2020)
Standard Practice for
Measuring Colorimetric Characteristics of Retroreflectors
Under Nighttime Conditions
This standard is issued under the fixed designation E811; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Editorial changes were made in Sections 2, 3, and 5 in June 2020.
1. Scope E691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method
1.1 This practice describes the instrumental determination
E808 Practice for Describing Retroreflection
of retroreflected chromaticity coordinates of retroreflectors. It
E809 Practice for Measuring Photometric Characteristics of
includes the techniques used in a photometric range to measure
Retroreflectors
retroreflected (nighttime) chromaticity with either a telecolo-
rimeter or telespectroradiometer. 2.2 CIE Documents:
CIE Publication No. 15 Colorimetry
1.2 This practice covers the general measurement proce-
ISO/CIE 11664-1:2019(E) Colorimetry — Part 1: CIE stan-
dures. Additional requirements for specific tests and specifica-
dard colorimetric observers
tions are described in Section 7.
ISO 11664-2:2007(E)/CIE S 014-2/E:2006 Colorimetry —
1.3 The description of the geometry used in the nighttime
Part 2: CIE Standard Illuminants for Colorimetry
colorimetry of retroreflectors is described in Practice E808 and
CIE Technical Report 54.2 Retroreflection: Definition and
the methods for calculation of chromaticity are contained in
Measurement
Practice E308.
1.4 This standard does not purport to address all of the
3. Terminology
safety concerns, if any, associated with its use. It is the
3.1 The terms and definitions inTerminology E284 apply to
responsibility of the user of this standard to establish appro-
this practice.
priate safety, health, and environmental practices and deter-
3.2 Definitions:
mine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accor- 3.2.1 chromaticity coordinates, n—the ratios of each of the
tristimulus values of a psychophysical color to the sum of the
dance with internationally recognized principles on standard-
tristimulus values.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom- 3.2.1.1 Discussion—Chromaticity coordinates in the CIE
mendations issued by the World Trade Organization Technical 1931 system of color specification are designated by x, y, z and
Barriers to Trade (TBT) Committee. in the CIE 1964 supplementary system by x , y , z .
10 10 10
3.2.2 CIE 1931 (x, y)-chromaticity diagram—the chroma-
2. Referenced Documents
ticity diagram for the CIE 1931 standard observer, in which the
2.1 ASTM Standards:
CIE 1931 chromaticity coordinates are plotted with x as the
E284 Terminology of Appearance
abscissa and y as the ordinate.
E308 PracticeforComputingtheColorsofObjectsbyUsing
3.2.3 CIE 1931 standard observer, n—ideal colorimetric
the CIE System
observer with color matching functions x¯(λ), y¯(λ), z¯(λ) corre-
sponding to a field of view subtending a 2° angle on the retina;
1 commonly called the “2° standard observer.”
This practice is under the jurisdiction of ASTM Committee E12 on Color and
Appearance and is the direct responsibility of Subcommittee E12.10 on Retrore-
3.2.3.1 Discussion—The color matching functions of the
flection.
CIE 1931 standard observer are tabulated in Practice E308,
Current edition approved June 15, 2020. Published July 2020. Originally
CIE Publication No. 15, and ISO/CIE 11664-1:2019(E).
approved in 1981. Last previous edition approved in 2015 as E811 – 09 (2015).
DOI: 10.1520/E0811-09R20E01.
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
Standards volume information, refer to the standard’s Document Summary page on Available from U.S. National Committee of the CIE (International Commission
the ASTM website. on Illumination) (http://www.cie-usnc.org) or the CIE (cie.co.at) Webshop.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959. United States
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E811−09 (2020)
3.2.4 CIE standard illuminant A, n—colorimetric 3.2.16 retroreflector center, n—a point on or near a retrore-
illuminant, representing the full radiation at 2855.6 K, defined flector that is designated to be the center of the device for the
by the CIE in terms of a relative spectral power distribution. purpose of specifying its performance.
3.2.4.1 Discussion—Therelativespectralpowerdistribution
3.2.17 rotation angle, ε,n—the angle in a plane perpendicu-
ofCIEstandardilluminant AistabulatedinPracticeE308,CIE
lar to the retroreflector axis from the observation halfplane to
Publication No. 15, and ISO 11664-2:2007(E)/CIE S 014-2/
the datum axis, measured counter-clockwise from a viewpoint
E:2006.
on the retroreflector axis.
3.2.17.1 Discussion—Range: –180°<ε≤180°. The definition
3.2.5 CIE standard source A, n—a gas-filled tungsten-
is applicable when entrance angle and viewing angle are less
filament lamp operated at a correlated color temperature of
B
than 90°. More generally, rotation angle is the angle from the
2855.6 K. [CIE]
positive part of second axis to the datum axis, measured
3.2.6 entrance angle, β,n—the angle between the illumina-
counterclockwise from a viewpoint on the retroreflector axis.
tion axis and the retroreflector axis.
3.2.17.2 Discussion—Rotation of the sample about the ret-
3.2.6.1 Discussion—The entrance angle is usually no larger
roreflector axis while the source and receiver remain fixed in
than 90°, but for completeness its full range is defined as 0° ≤
space changes the rotation angle (ε) and the orientation angle
β≤180°.IntheCIE(goniometer)systemβisresolvedintotwo
(ω ) equally.
s
components,β andβ .Sincebydefinitionβisalwayspositive,
1 2
3.2.18 spectroradiometer, n—an instrument for measuring
the common practice of referring to the small entrance angles
the spectral distribution of radiant energy or power.
that direct specular reflections away from the photoreceptor as
negative valued is deprecated byASTM. The recommendation 3.2.19 tristimulus colorimeter, n—instrument that measures
psychophysical color, in terms of tristimulus values, by the use
is to designate such negative values as belonging to β .
of filters to convert the relative spectral power distribution of
3.2.7 goniometer, n—an instrument for measuring or setting
the illuminator to that of a standard illuminant, and to convert
angles.
the relative spectral responsivity of the receiver to the respon-
3.2.8 illumination axis, n—in retroreflection, a line from the
sivities prescribed for a standard observer.
effective center of the source aperture to the retroreflector
3.2.19.1 Discussion—In some instruments, the filters may
center.
be combined into one set placed in the receiver; in such cases,
3.2.9 observation angle, n—angle between the axes of the caution should be observed when measuring fluorescent speci-
incident beam and the observed (reflected) beam, (in mens.
retroreflection, α, angle between the illumination axis and the
3.2.20 viewing angle, v, n—in retroreflection, the angle
observation axis).
between the retroreflector axis and the observation axis.
3.2.10 observation axis, n—in retroreflection, a line from
3.3 Definitions of Terms Specific to This Standard:
the effective center of the receiver aperture to the retroreflector
3.3.1 telecolorimeter, n—a tristimulus colorimeter equipped
center.
with collection optics for viewing a limited area at a distance
from the instrument.
3.2.11 retroreflection, n—reflection in which the reflected
rays are preferentially returned in directions close to the
3.3.2 telespectroradiometer, n—a spectroradiometer
opposite of the direction of the incident rays, this property
equipped with collection optics for viewing a limited area at a
being maintained over wide variations of the direction of the
distance from the instrument.
incident rays.
4. Summary of Practice
3.2.12 retroreflective device, n—deprecated term; use ret-
roreflector. 4.1 Two procedures are described in this practice (see also
Practice E809). Procedure A is based on a calibrated light
3.2.13 retroreflective sheeting, n—a retroreflective material
source,coloredreferencefilters,awhitereferencestandardand
preassembled as a thin film ready for use.
a telecolorimeter equipped with tristimulus filters. In this
3.2.14 retroreflector, n—a reflecting surface or device from
procedure, measurements of the incident light on the white
which, when directionally irradiated, the reflected rays are
standard at the specimen position are made using the colored
preferentially returned in directions close to the opposite of the
filters and correction factors developed.Then the retroreflected
direction of the incident rays, this property being maintained
light is measured under the test geometry and the corrected
over wide variations of the direction of the incident rays.
relative tristimulus values are computed. In Procedure B,
3.2.15 retroreflector axis, n—a designated line segment spectralmeasurementsaremadeoftheincidentlightandofthe
from the retroreflector center that is used to describe the retroreflected light under the test geometry required. From
angular position of the retroreflector. these spectral measurements, the relative tristimulus values are
determined.Inbothprocedures,thechromaticitycoordinates x,
3.2.15.1 Discussion—The direction of the retroreflector axis
y are based on the CIE 1931 Standard Color Observer.
is usually chosen centrally among the intended directions of
illumination;forexample,thedirectionoftheroadonwhichor
5. Significance and Use
with respect to which the retroreflector is intended to be
positioned. In testing horizontal road markings the retroreflec- 5.1 This practice describes a procedure for measuring the
tor axis is usually the normal to the test surface. chromaticity of retroreflectors in a nighttime, that is,
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E811−09 (2020)
retroreflective, geometry of illumination and observation. CIE 6.3 CIE 1931 (x, y) Chromaticity Diagram—The chroma-
Standard Source A has been chosen to represent a tungsten ticity coordinates x and y can be plotted as shown in Practice
automobile headlamp. Although the geometry must be speci- E308, Fig. 1.The outline in the figure encloses the entire range
fied by the user of this practice, it will, in general, correspond of combinations of x and y that correspond to real colors. The
to the relationship between the vehicle headlamp, the points at which monochromatic radiation of various wave-
retroreflector, and the vehicle driver’s eyes. Thus, the chroma- lengths falls are indicated on this boundary, with the more
ticity coordinates determined by the procedures in this practice nearly neutral colors being represented by points toward the
describe numerically the nighttime appearance of the retrore- center of the bounded region.
flector.
6.4 Specifying Color Limits—Acolor point representing the
xandychromaticitycoordinatesofatestsamplecanbelocated
6. Use of the CIE Chromaticity Diagram for the
on the CIE diagram. A specification for a specific retroreflec-
Specification of Color
tive color limit would require that the color point for a sample
of this color fall within specified boundaries of the diagram.
6.1 Tristimulus Values for a Colored Sample—The spectral
The area within these boundaries is referred to as a color area,
nature of the light coming to the eye from a retroreflector
and is defined exactly by specifying four sets of chromaticity
depends upon the spectral distribution of the radiation from the
coordinates in the specification.
source, S(λ), and a quantity proportional to the spectral
reflectance of the retroreflector, R(λ). For nighttime colorimet-
6.5 Daytime versus Nighttime Color Limits—Different color
ric measurements of retroreflectors, S(λ) is Illuminant A. The
limits are required to specify daytime and nighttime color.
spectral tristimulus values, x¯, y¯, and z¯, the illuminant power
Nighttime and daytime color limits are different for two major
S(λ), and the reflectance quantity R(λ) are used together to
reasons: the quality of the illuminating light and the geometry
calculate three numbers, the tristimulus values X, Y, and Z as
or direction of the illuminating light. Daytime color is viewed
follows:
under a source of daylight quality, and nighttime color is
viewed under Source A (a CIE source corresponding to an
X 5 k S λ R λ x¯ λ dλ
* ~ ! ~ ! ~ ! incandescent lamp, such as an automobile headlamp). Illumi-
A
nation in the daytime is from skylight, and diffusely reflected
light is observed; illumination in the nighttime comes from a
Y 5 k * S ~λ! R~λ! y¯~λ!dλ
A
point very near the observer, and retroreflected light is ob-
served.
Z 5 k S ~λ! R~λ! z¯~λ!dλ
*
A
7. Requirements to be Stated in Specifications
7.1 When stating colorimetric retroreflective requirements,
where:
the following requirements shall be given in the specification
S (λ) = spectral power distribution of Illuminant
A
for the material:
A,
7.1.1 Limits of the color area on the 1931 CIE chromaticity
R(λ) = spectral reflectance factor of the sample,
diagram (usually four pairs of chromaticity coordinates (x and
and
y) are required to define an area on the diagram).
x¯(λ), y¯(λ), z¯(λ) = color matching functions of the CIE stan-
7.1.2 Chromaticity coordinate limits and spectral transmit-
dard observer.
tance limits of the standard filter when Procedure A is used.
(These may be specified by giving the filter glass type and
100/k 5 S y¯ λ dλ
* ~ !
A
thickness or the manufacturer’s part number of the filter.)
7.1.3 Observation angle (α).
Integration of each curve across the visible region (380 to
7.1.4 Entrance angle (β) and when required the components
740 nm) give the numerical value for the corresponding
of the entrance angle β , and β . (When specifying entrance
1 2
tristimulus value X, Y, or Z.
angles near 0°, care must be taken to prevent “white” specular
reflection from entering the receptor. Therefore, instead of
6.2 Chromaticity Coordinates—The chromaticity coordi-
specifying 0°, the entrance angle is usually specified so that
nates x, y, and z are computed from the tristimulus values X, Y,
specular light is reflected away from the receptor.)
and Z as follows:
7.1.5 Rotation angle (ε) and the location of the datum mark,
x 5 X/ X1Y1Z
~ !
if random orientation of the test specimen is not suitable.
y 5 Y/ X1Y1Z
~ !
7.1.6 Observation distance (d).
z 5 Z/ X1Y1Z
~ !
7.1.7 Test specimen dimensions and shape.
The normalization constant k in the equations for X, Y, and 7.1.8 Receptor angular aperture, usually either 6 min or 10
Z cancels out in calculating x, y, and z.Thus, x, y, and z express min of arc.
the color of the reflected light without regard to its intensity. 7.1.9 Source angular aperture, usually either 6 min or 10
Because the sum of x, y, and z is always equal to one, only two min of arc.
of these quantities are needed to describe the chromaticity of a 7.1.10 Reference center of the retroreflector.
light. The chromaticity coordinates x and y are chosen for this 7.1.11 Reference axis of the retroreflector. (The reference
purpose. axis is usually perpendicular to the surface of sheeting. In such
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E811−09 (2020)
complex devices as automobile or bicycle reflectors, the telecolorimeter, and test samples as required so that the
referenceaxisandreferencecentermaybedefinedwithrespect geometric arrangement required for calibration and measure-
to the viewing direction.) ments can be achieved and maintained.
8.6 Photometric Range—The background behind the
8. Apparatus
sample shall be flat black to minimize the effect of stray light.
8.1 The apparatus shall consist of either a spectroradiometer Light baffles shall be located, as necessary, between the
projector and the test sample. Goniometer parts, range wall,
equipped with collection optics or a telecolorimeter, a regu-
lated light projector source, a goniometer sample holder, a ceiling,andfloorexposedtothelightbeamshallbepaintedflat
black.
photometric range, and calibration standards.
8.2 Telecolorimeter—The telecolorimeter shall be equipped
9. Test Specimen and Sample
with three or more filters having spectral transmittances such
9.1 The test specimen is the unit on which the test is made.
that the spectral products of CIE Illuminant A with CIE
The specimen is the material selected by a sampling process
tristimulus functions x-bar, y-bar, and z-bar are each linear
which is not part of this practice.
combinations of the spectral products of the instrument
illumination, the instrument detector sensitivity, and the three
9.2 The test specimen should be one entire retroreflector (a
or more filters transmittances.
large retroreflector may be tested by summing the effects of
8.2.1 Discussion—If the Instrument illumination matches
smaller segments).
CIE Illuminant A, then the condition simplifies to the CIE
9.3 When testing retroreflective sheeting, a minimum area
Tristimulus functions x-bar, y-bar, and z-bar each being linear
of 0.1 (60.05) m should be used. This may be accomplished
combinations of
...