ASTM E811-95(2001)
(Practice)Standard Practice for Measuring Colorimetric Characteristics of Retroreflectors Under Nighttime Conditions
Standard Practice for Measuring Colorimetric Characteristics of Retroreflectors Under Nighttime Conditions
SIGNIFICANCE AND USE
This practice describes a procedure for measuring the color appearance of retroreflectors as seen under nighttime conditions of illumination and viewing. CIE Standard Source A has been chosen to represent a tungsten automobile headlamp. Although the geometry must be specified by the user of this practice, it will, in general, correspond to the relationship between the vehicle headlamp, the retroreflector, and the vehicle driver’eyes. Thus, the chromaticity coordinates determined by the procedures in this practice describe numerically the nighttime appearance of the retroreflector.5
SCOPE
1.1 This practice describes the instrumental determination of retroreflected chromaticity coordinates of retro- reflectors. It includes the techniques used in a photometric range to measure retroreflected (nighttime) chromaticity with either a telecolorimeter or telespectroradiometer.
1.2 This practice covers the general measurement procedures. Additional requirements for specific tests and specifications are described in Section 7.
1.3 The description of the geometry used in the nighttime colorimetry of retroreflectors is described in Practice E808 and the methods for calculation of chromaticity are contained in Test Method E308.
1.4 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: E811 – 95 (Reapproved 2001)
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.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope CIE Standard S001/ISO IS 10526, Colorimetric Illumi-
nants
1.1 This practice describes the instrumental determination
CIEStandardS002/ISO IS10527,ColorimetricObservers
of retroreflected chromaticity coordinates of retroreflectors. It
includesthetechniquesusedinaphotometricrangetomeasure
3. Terminology
retroreflected (nighttime) chromaticity with either a telecolo-
3.1 ThetermsanddefinitionsinTerminologyE284applyto
rimeter or telespectroradiometer.
this practice.
1.2 This practice covers the general measurement proce-
3.2 Definitions:
dures.Additional requirements for specific tests and specifica-
3.2.1 chromaticity coordinates, n—the ratios of each of the
tions are described in Section 7.
tristimulus values of a psychophysical color to the sum of the
1.3 The description of the geometry used in the nighttime
tristimulus values.
colorimetryofretroreflectorsisdescribedinPracticeE808and
3.2.1.1 Discussion—Chromaticity coordinates in the CIE
the methods for calculation of chromaticity are contained in
1931systemofcolorspecificationaredesignatedby x, y, zand
Practice E308.
in the CIE 1964 supplementary system by x , y , z .
10 10 10
1.4 This standard does not purport to address all of the
3.2.2 CIE 1931 (x, y)-chromaticity diagram—the chroma-
safety concerns, if any, associated with its use. It is the
ticitydiagramfortheCIE1931standardobserver,inwhichthe
responsibility of the user of this standard to establish appro-
CIE 1931 chromaticity coordinates are plotted with x as the
priate safety and health practices and determine the applica-
abscissa and y as the ordinate.
bility of regulatory limitations prior to use.
3.2.3 CIE 1931 standard observer, n—ideal colorimetric
2. Referenced Documents observer with color matching functions x¯ (l), y¯ (l), z¯ (l)
corresponding to a field of view subtending a 2° angle on the
2.1 ASTM Standards:
B
retina; commonly called the “2° standard observer.” [CIE]
E284 Terminology of Appearance
3.2.3.1 Discussion—The color matching functions of the
E308 Practice for Computing the Colors of Objects by
CIE 1931 standard observer are tabulated in Practice E308,
Using the CIE System
CIE Publication 15.2, and CIE Standard S002.
E808 Practice for Describing Retroreflection
3.2.4 CIE standard illuminant A, n—colorimetric illumi-
E809 PracticeforMeasuringPhotometricCharacteristicsof
nant,representingthefullradiationat2855.6K,definedbythe
Retroreflectors
B
CIE in terms of a relative spectral power distribution. [CIE]
2.2 CIE Documents:
3.2.4.1 Discussion—The relative spectral power distribu-
CIE Publication No.15.2 Colorimetry, 2d ed.
tionofCIEstandardilluminant AistabulatedinPracticeE308,
CIE Publication 15.2, and CIE Standard S001.
3.2.5 CIE standard source A, n—a gas-filled tungsten-
This practice is under the jurisdiction ofASTM Committee E12 on Color and
filament lamp operated at a correlated color temperature of
Appearance and is the direct responsibility of Subcommittee E12.10 on Retrore-
B
2855.6 K. [CIE]
flection.
3.2.6 entrance angle, b, n—in retroreflection, angle be-
Current edition approved June 10, 2001. Published July 2001. Originallyap-
proved in 1981. Last previous edition approved in 2001 as E811–95(2001). DOI:
tween the illumination axis and the retroreflector axis.
10.1520/E0811-95R01.
3.2.6.1 Discussion—The entrance angle is usually no larger
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
than 90°, but for completeness its full range is defined as 0°#
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
the ASTM website.
3 4
AvailablefromU.S.NationalCommitteeoftheCIE(InternationalCommission Stephenson, H. F., “The Colorimetric Measurement of Retroreflective Materi-
on Illumination), C/o Thomas M. Lemons, TLA-Lighting Consultants, Inc., 7 Pond als. Progress Report on International Exchange Tests.” Proceedings of the CIE,
St., Salem, MA 01970, http://www.cie-usnc.org. 18th Session (London), pp. 595–609, 1975.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E811 – 95 (2001)
b# 180°. To completely specify the orientation, this angle is 3.2.19.1 Discussion—In some instruments, the filters may
characterized by two components, b and b . be combined into one set placed in the receiver; in such cases,
1 2
caution should be observed when measuring fluorescent speci-
3.2.7 goniometer, n—aninstrumentformeasuringorsetting
mens.
angles.
3.2.20 viewing angle, v, n—in retroreflection, the angle
3.2.8 illumination axis, n—in retroreflection,alinefromthe
between the retroreflector axis and the observation axis.
effective center of the source aperture to the retroreflector
3.3 Definitions of Terms Specific to This Standard:
center.
3.3.1 telecolorimeter, n—atristimuluscolorimeterequipped
3.2.9 observation angle, n—angle between the axes of the
with collection optics for viewing a limited area at a distance
incident beam and the observed (reflected) beam, (in retrore-
from the instrument.
flection, a, angle between the illumination axis and the
3.3.2 telespectroradiometer, n—a spectroradiometer
observation axis).
equipped with collection optics for viewing a limited area at a
3.2.10 observation axis, n—in retroreflection, a line from
distance from the instrument.
the effective center of the receiver aperture to the retroreflector
center.
4. Summary of Practice
3.2.11 retroreflection, n—reflection in which the reflected
4.1 Two procedures are described in this practice (see also
rays are preferentially returned in directions close to the
Practice E809). Procedure A is based on a calibrated light
opposite of the direction of the incident rays, this property
source,coloredreferencefilters,awhitereferencestandardand
being maintained over wide variations of the direction of the
a telecolorimeter equipped with tristimulus filters. In this
B
incident rays. [CIE]
procedure, measurements of the incident light on the white
3.2.12 retroreflective device, n—deprecated term; use ret-
standard at the specimen position are made using the colored
roreflector.
filtersandcorrectionfactorsdeveloped.Thentheretroreflected
3.2.13 retroreflective sheeting, n—a retroreflective material
light is measured under the test geometry and the corrected
preassembled as a thin film ready for use.
relative tristimulus values are computed. In Procedure B,
3.2.14 retroreflector, n—a reflecting surface or device from
spectralmeasurementsaremadeoftheincidentlightandofthe
which, when directionally irradiated, the reflected rays are
retroreflected light under the test geometry required. From
preferentiallyreturnedindirectionsclosetotheoppositeofthe
thesespectralmeasurements,therelativetristimulusvaluesare
direction of the incident rays, this property being maintained
determined.Inbothprocedures,thechromaticitycoordinates x,
overwidevariationsofthedirectionoftheincidentrays.[CIE,
y are based on the CIE 1931 Standard Color Observer.
B
1982]
3.2.15 retroreflector axis, n—a designated line segment 5. Significance and Use
from the retroreflector center that is used to describe the
5.1 This practice describes a procedure for measuring the
angular position of the retroreflector.
color appearance of retroreflectors as seen under nighttime
3.2.15.1 Discussion—Thedirectionoftheretroreflectoraxis
conditionsofilluminationandviewing.CIEStandardSourceA
is usually chosen centrally among the intended directions of
has been chosen to represent a tungsten automobile headlamp.
illumination;forexample,thedirectionoftheroadonwhichor
Although the geometry must be specified by the user of this
with respect to which the retroreflector is intended to be
practice, it will, in general, correspond to the relationship
positioned. In testing horizontal road markings the retroreflec-
between the vehicle headlamp, the retroreflector, and the
tor axis is usually the normal to the test surface.
vehicle driver’s eyes. Thus, the chromaticity coordinates de-
3.2.16 retroreflector center, n—a point on or near a retrore- termined by the procedures in this practice describe numeri-
flector that is designated to be the center of the device for the
cally the nighttime appearance of the retroreflector.
purpose of specifying its performance.
3.2.17 rotation angle, ´, n—inretroreflection,angleindicat- 6. Use of the CIE Chromaticity Diagram for the
Specification of Color
ing the orientation of the specimen when it is rotated about the
retroreflector axis.
6.1 Tristimulus Values for a Colored Sample—The spectral
3.2.17.1 Discussion—The rotation angle is the dihedral
nature of the light coming to the eye from a retroreflector
angle from the half-plane originating on the retroreflector axis dependsuponthespectraldistributionoftheradiationfromthe
and containing the positive part of the second axis to the half
source, S (l), and a quantity proportional to the spectral
plane originating on the retroreflector axis and containing the reflectance of the retroreflector, R (l). For nighttime colori-
datum mark. Range:−180°# ´# 180°.
metric measurements of retroreflectors, S (l) is Illuminant A.
The spectral tristimulus values, x¯, y¯, and z, the illuminant
3.2.18 spectroradiometer, n—an instrument for measuring
power S (l), and the reflectance quantity R (l) are used
the spectral distribution of radiant energy or power.
togethertocalculatethreenumbers,thetristimulusvalues X, Y,
3.2.19 tristimulus colorimeter, n—instrument that measures
and Z as follows:
psychophysicalcolor,intermsoftristimulusvalues,bytheuse
of filters to convert the relative spectral power distribution of
the illuminator to that of a standard illuminant, and to convert
the relative spectral responsivity of the receiver to the respon-
Rennilson, J. J., “Chromaticity Measurements of Retroreflective Material
sivities prescribed for a standard observer. Under Nighttime Geometry,” Applied Optics , Vol 45, April 15, 1980.
E811 – 95 (2001)
nearly neutral colors being represented by points toward the
X 5 k S ~l! R~l! x¯~l!dl
* A
center of the bounded region.
6.4 Specifying Color Limits—Acolor point representing the
xand ychromaticitycoordinatesofatestsamplecanbelocated
Y 5 k S l R l y¯ l dl
~ ! ~ ! ~ !
* A
on the CIE diagram. A specification for a specific retroreflec-
tive color limit would require that the color point for a sample
of this color fall within specified boundaries of the diagram.
Z 5 k S ~l! R~l! z¯~l!dl
*
A
The area within these boundaries is referred to as a color area,
and is defined exactly by specifying four sets of chromaticity
where: coordinates in the specification.
S (l) = spectral power distribution of Illumi-
6.5 Daytime versus Nightime Color Limits—Different color
A
nant A,
limits are required to specify daytime and nighttime color.
R(l) = spectralreflectancefactorofthesample,
Nighttime and daytime color limits are different for two major
and
reasons: the quality of the illuminating light and the geometry
x¯(l), y¯(l), z¯(l) = color matching functions of the CIE
or direction of the illuminating light. Daytime color is viewed
standard observer.
under a source of daylight quality, and nighttime color is
viewed under Source A (a CIE source corresponding to an
100/k 5 S y¯~l!dl
* A
380 incandescent lamp, such as an automobile headlamp). Illumi-
nation in the daytime is from skylight, and diffusely reflected
Integration of each curve across the visible region (380 to
light is observed; illumination in the nighttime comes from a
740 nm) give the numerical value for the corresponding
point very near the observer, and retroreflected light is ob-
tristimulus value X, Y, or Z.
served.
6.2 Chromaticity Coordinates—The chromaticity coordi-
nates x, y,and zarecomputedfromthetristimulusvalues X, Y,
7. Requirements to be Stated in Specifications
and Z as follows:
7.1 When stating colorimetric retroreflective requirements,
x 5 X/~X 1 Y 1 Z!
the following requirements shall be given in the specification
y 5 Y/ X 1 Y 1 Z
~ !
for the material:
7.1.1 Limits of the color area on the 1931 CIE chromaticity
z 5 Z/~X 1 Y 1 Z!
diagram (usually four pairs of chromaticity coordinates (x and
The normalization constant k in the equations for X, Y, and
y) are required to define an area on the diagram).
Zcancelsoutincalculating x, y,and z.Thus, x, y,and zexpress
7.1.2 Chromaticity coordinate limits and spectral transmit-
the color of the reflected light without regard to its intensity.
tance limits of the standard filter when Procedure A is used.
Becausethesumof x, y,and zisalwaysequaltoone,onlytwo
(These may be specified by giving the filter glass type and
of these quantities are needed to describe the chromaticity of a
thickness or the manufacturer’s part number of the filter.)
light. The chromaticity coordinates x and y are chosen for this
7.1.3 Observation angle (a).
purpose.
7.1.4 Entranceangle(b)andwhenrequiredthecomponents
6.3 CIE 1931 (x, y) Chromaticity Diagram—The chroma-
of the entrance angle b , and b . (When specifying entrance
1 2
ticity coordinates x and y can be plotted as shown in Practice
angles near 0°, care must be taken to prevent “white” specular
E308,Fig.1.Theoutlineinthefigureenclosestheentirerange
reflection from entering the receptor. Therefore, instead of
of combinations of x and y that correspond to real colors. The
specifying 0°, the entrance angle is usually specified so that
points at which monochromatic radiation of various wave-
specular light is reflected away from the receptor.)
lengths falls are indicated on this boundary, with the more
7.1.5 Rotationangle(´)andthelocationofthedatummark,
if random orientation of the test specimen is not suitable.
7.1.6 Observation distance (d).
7.1.7 Test specimen dimensions and shape.
7.1.8 Receptor angular aperture, usually 6 min of arc.
7.1.9 Source angular aperture, usually 6 min of arc.
7.1.10 Reference center of the retroreflector.
7.1.11 Reference axis of the retroreflector. (The reference
axisisusuallyperpendiculartothesurfaceofsheeting.Insuch
complex devices as automobile or bicycle reflectors, the
referenceaxisandreferencecentermaybedefinedwithrespect
to the viewing direction.)
8. Apparatus
8.1 Theapparatusshallconsistofeitheraspectrorad
...
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