ASTM E809-08(2013)
(Practice)Standard Practice for Measuring Photometric Characteristics of Retroreflectors
Standard Practice for Measuring Photometric Characteristics of Retroreflectors
SIGNIFICANCE AND USE
5.1 This practice describes procedures used to measure photometric quantities that relate to the visual perception of retroreflected light. The most significant usage is in the relation to the nighttime vehicle headlamp, retroreflector, and driver's eye geometry. For this reason the CIE Standard Source A is used to represent a tungsten vehicle headlamp and the receptor has the photopic, V (λ), spectral responsivity corresponding to the light adapted human eye. Although the geometry must be specified by the user, it will, in general, correspond to the relation between the vehicle headlamp, the retroreflector, and the vehicle driver's eye position.
SCOPE
1.1 This practice describes the general procedures for instrumental measurement of the photometric characteristics of retroreflective materials and retroreflective devices.
1.2 This practice is a comprehensive guide to the photometry of retroreflectors but does not include geometric terms that are described in Practice E808.
1.3 This practice describes the parameters that are required when stating photometric measurements in specific tests and specifications for retroreflectors.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
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.
General Information
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: E809 −08 (Reapproved 2013)
Standard Practice for
Measuring Photometric Characteristics of Retroreflectors
This standard is issued under the fixed designation E809; 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 3. Terminology
1.1 This practice describes the general procedures for in- 3.1 Terms and definitions in Terminology E284 and E808
strumental measurement of the photometric characteristics of
are applicable to this practice. In general, the terminology in
retroreflective materials and retroreflective devices.
this practice agrees with that in CIE Publications DS 17.2/
E:2009 and 54.2.
1.2 This practice is a comprehensive guide to the photom-
etryofretroreflectorsbutdoesnotincludegeometrictermsthat
3.2 Definitions of Terms Specific to This Standard:
are described in Practice E808.
3.2.1 annular aperture, n—the difference between the an-
gulardiametersoftheexternalboundarycircleandtheinternal
1.3 This practice describes the parameters that are required
boundary circle.
when stating photometric measurements in specific tests and
specifications for retroreflectors.
3.2.2 circular aperture, n—the angular diameter of a circu-
lar aperture surface.
1.4 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
3.2.3 goniometer, n—an instrument for measuring or setting
standard.
angles.
1.5 This standard does not purport to address all of the
3.2.4 photopic receiver, n—a receiver of radiation with a
safety concerns, if any, associated with its use. It is the
spectral responsivity which conforms to the V (λ) distribution
responsibility of the user of this standard to establish appro-
of the CIE Photopic Standard Observer that is specified in
priate safety and health practices and determine the applica-
Practice E308.
bility of regulatory limitations prior to use.
3.2.5 receiver aperture, n—angular dimensions from the
retroreflector center to the entrance aperture or pupil of the
2. Referenced Documents
receiver.
2.1 ASTM Standards:
3.2.6 rectangular aperture, n—the angular height and width
E284Terminology of Appearance
of a rectangular aperture surface.
E308PracticeforComputingtheColorsofObjectsbyUsing
3.2.6.1 Discussion—The orientation of the sides of the
the CIE System
rectangular aperture surface should be supplied together with
E808Practice for Describing Retroreflection
the angular height and width.
2.2 CIE Documents:
CIE Publication No. 54.2Retroreflection—Definition and 3.2.7 reflected illuminance, E,n—illuminance at the re-
r
Measurement ceiver measured on a plane perpendicular to the observation
CIE Publication DS 17.2/E:2009International Lighting Vo- axis.
cabulary
3.2.7.1 Discussion—This quantity is used in the calculation
CIE Publication No. 69-1987Methods of Characterizing of the coefficient of luminous intensity,
Illuminance Meters and Luminance Meters
R: R =(I/E )=(E d )/E , where d is the distance from the
I I ' r '
retroreflector to the receptor.
1 3.2.8 retroreflectometer aperture angles, n—the maximum
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- angular diameter of the pencil of light (see Fig. 1).
flection.
3.2.8.1 Discussion—In practice the illumination arrives at
Current edition approved Jan. 1, 2013. Published January 2013. Originally
the retroreflector center within a narrow pencil of light sur-
approved in 1981. Last previous edition approved in 2008 as E809–08. DOI:
rounding the illumination axis and the light reflected to the
10.1520/E0809-08R13.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
photoreceptor is contained within another narrow pencil. The
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
distribution of light within such pencils is the “aperture”
Standards volume information, refer to the standard’s Document Summary page on
functionandthemaximumangulardiameterofthepencilisthe
the ASTM website.
Available from the CIE Webshop at http://www.cie.co.at. “aperture angle.” It is generally assumed that the aperture
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E809 − 08 (2013)
to the nighttime vehicle headlamp, retroreflector, and driver’s
eye geometry. For this reason the CIE Standard Source A is
used to represent a tungsten vehicle headlamp and the receptor
has the photopic, V (λ), spectral responsivity corresponding to
the light adapted human eye. Although the geometry must be
specified by the user, it will, in general, correspond to the
relation between the vehicle headlamp, the retroreflector, and
the vehicle driver’s eye position.
6. Uses and Applications
FIG. 1 Illustration of Apertures used in Retroreflection Measure-
ment
6.1 Coeffıcient of Retroreflection—This quantity is used to
specifytheperformanceofretroreflectivesheeting.Itconsiders
the retroreflector as an apparent point source whose retrore-
functions are rotationally symmetrical and even uniform, but
flected luminous intensity is dependent on the area of the
this is often false, especially for illumination.
retroreflective surface involved. It is a useful engineering
3.2.9 retroreflectoraperturesurface,n—theaperturesurface
quantity for determining the photometric performance of such
of a retroreflector is given by the retroreflector itself, or by a
retroreflective surfaces as highway delineators or warning
diaphragm enclosing part of the retroreflector.
devices. The coefficient of retroreflection may also be used to
determine the minimum area of retroreflective sheeting neces-
3.2.10 retroreflector element aperture, n—angular dimen-
sary for a desired level of photometric performance.
sion of the aperture surface of a retroreflective element as seen
from the receiver’s center.
6.2 Coeffıcient of Luminous Intensity—This term is used to
3.2.10.1 Discussion—The element aperture quantifies an
specify the performance of retroreflective devices. It considers
error source in the setting of the observation angle. This is a
the retroreflected luminous intensity as a function of the
critical feature for testing large retroreflective elements or at
perpendicular illuminance incident on the device. It is recom-
short distances. When using collimated optics, placing the
mended for use in describing performance of RPMs, taillight
sourceandreceiveratvirtualinfinity,theretroreflectorelement
reflex reflectors and roadway delineators.
aperture is virtually zero.
6.3 Coeffıcient of Line Retroreflection (of a Reflecting
3.2.11 retroreflector (or specimen) aperture, n—angular di-
Stripe)—This term may be used to describe the retroreflective
mensions from the source point of reference to the aperture
performance of long narrow strips of retroreflective materials,
surface of the retroreflector (or specimen).
when the actual width is not as important as is the reflectivity
3.2.11.1 Discussion—As the source and receiver are gener-
per unit length.
ally close to each other, distinction is not made between
aperture angles seen from the source and receiver.When using 6.4 Reflectance Factor (of a Plane Reflecting Surface)—
This is a useful term for comparing surfaces specifically
collimated optics where the source and receiver are at virtual
infinity, the retroreflector aperture is virtually naught. The designed for retroreflection to surfaces which are generally
considered to be diffuse reflectors. Since almost all natural
retroreflector aperture describes the maximum variation of the
entrance angle of the aperture surface of the retroreflector. surfaces tend to retroreflect slightly, materials such as BaSO
canhaveareflectancefactormuchhigherthanone(asmuchas
3.2.12 source aperture, n—angular dimensions from the
four) at small observation angles. Such diffuse reflectance
retroreflector center to the exit aperture stop or pupil of the
standards should be used for calibration only at large observa-
light source.
tion angles, for example, 45°.
4. Summary of Practice
6.5 Coeffıcient of Retroreflected Luminance (also called
4.1 The fundamental procedure described in this practice Specific Luminance)—This term considers the retroreflector as
involves measurements of retroreflection based on the ratio of
a surface source whose projected area is visible as an area at
the retroreflected illuminance at the observation position to the the observation position. The coefficient of retroreflected
incident illuminance measured perpendicular to the illumina-
luminance relates to the way the effective retroreflective
tion axis at the retroreflector. From these measurements, along surface is focused on the retina of the human eye and to the
with the geometry of test, various photometric quantities visual effect thereby produced. It is recommended for describ-
applicable to retroreflectors can be determined. ing the performance of highway signs and striping or large
vehicularmarkingswhicharecommonlyviewedasdiscernible
4.2 Also described are methods of comparative testing
surface areas.
where unknown specimens are measured relative to an agreed-
upon standard retroreflector (a substitution test method).
6.6 Coeffıcient of Luminous Flux per Unit Solid Angle,
R —This measurement is used to evaluate retroreflectors on
Φ
5. Significance and Use
the basis of flux ratios. It is numerically very nearly equal to
5.1 This practice describes procedures used to measure the coefficient of retroreflected luminance at small entrance
photometric quantities that relate to the visual perception of angles. It is recommended for use in the design of retroreflec-
retroreflectedlight.Themostsignificantusageisintherelation tors but not for specification purposes.
E809 − 08 (2013)
7. Requirements When Measuring Retroreflectors an observer goniometer, (sometimes known as the observation
angle positioner), and a photometric range.
7.1 When describing photometric measurements of
8.1.1 Aperture angles are a very important consideration
retroreflectors, items in paragraphs 7.1.1 – 7.1.11 must be
when measuring retroreflectors as Fig. 1 illustrates. See Table
included. Refer to Fig. 2 for a diagram of measurement
1 for recommendations for maximum angular aperture of
geometry terminology.
optical elements. See 9.1 on selection of angular apertures.
7.1.1 Retroreflective photometric quantity, such as: coeffi-
cient of luminous intensity (R), coefficient of retroreflected
I
8.2 Photoreceptor—The photoreceptor shall be equipped as
luminance (R ) (also called specific luminance), coefficient of
L
follows:
retroreflection (R ), coefficient of line retroreflection (R ),
A M
8.2.1 Photopic Filter—The photoreceptor shall be equipped
reflectance factor (R ), or coefficient of luminous flux per unit
F
with a light filter such that the spectral responsivity of the
solid angle (R ).
Φ
receptor should match the V(λ) response of the CIE Standard
7.1.1.1 Inspecifications,aminimumacceptablequantitative
photopic observer with an f ' tolerance no greater than 3%.
value is usually established.
Spectral correction filters to the V(λ) function may be used
7.1.2 Units in which each quantity is to be measured (for
−1 −2
provided that they are determined on material which has been
example cd·lx ·m ).
previously measured by spectroradiometric means and closely
7.1.3 Observation angle.
correspondsintheirspectralcoefficientofretroreflectiontothe
7.1.4 Components of the entrance angle, (β and β ).
1 2
specimen under test. See Annex A1 for uncertainty tests and
7.1.4.1 When both β and β are near zero, care must be
1 2
compensation.
taken to prevent specular reflection from entering the photore-
8.2.2 Photoreceptor Stability and Linearity—The stability
ceptor.
−1
and linearity of the photometric scale reading must be within
7.1.4.2 Entrance angle β equals cos (cosβ cosβ ).
1 2
7.1.5 Rotation angle and the datum mark position shall be 1% over the range of values to be measured (see Annex A2).
The responsivity and range of the photoreceptor should be
specified if random rotational orientation of the test specimen
is not suitable. sufficient such that readings of the projector light source and
the retroreflector under test will have a resolution of at least 1
7.1.6 Test distance or minimum test distance.
7.1.7 Test specimen size and shape. part in 50.
7.1.8 Photoreceptor angular aperture.
8.2.3 Photoreceptor Angular Aperture—The photoreceptor
7.1.9 Source angular aperture.
must be equipped with a means to limit the angular collection
7.1.10 Retroreflector center.
of retroreflective luminous flux. This may be accomplished
7.1.11 Retroreflector axis. The retroreflector axis is usually
with an objective lens and field aperture or with light baffling.
perpendicular to the surface of retroreflective sheeting. In such
The field of view shall be limited such that the effect of stray
complex devices as automobile or bicycle reflectors, the
light is negligible. The field of view should be limited to the
retroreflectoraxisandretroreflectorcentermaybedefinedwith
smallest aperture that includes the entire test specimen or the
respect to the illumination direction.
illuminated area when testing horizontal coating materials.
When an objective lens is used, it shall be capable of focusing
8. Apparatus
atthetestdistance.Angularaperturesforthephotoreceptorare
8.1 General—The apparatus shall consist of a specified in degrees subtended at the specimen.The responsiv-
photoreceptor,alightprojectorsource,aspecimengoniometer, ity across the aperture shall be uniform.
FIG. 2 View of Test Geometer for Measuring Retroreflection
E809 − 08 (2013)
A
TABLE 1 Optical Element Angular Apertures
9.1.1 Standard Circular Apertures—The following uniform
Standard apertures 0.05° 0.−1° 0.167° 0.333°
circular apertures are considered standard.
Angular aperture of an individual 0.01° 0.02° 0.04° 0.08°
9.1.1.1 0.05° (3 arc min) for both light source and photore-
retroreflective element, ° max max max max
ceptor.
A
Optical element angular aperture maximum requirements apply to all non-
9.1.1.2 0.1° (6 arc min) for both light source and photore-
collimating instruments.
ceptor.
9.1.1.3 0.167° (10 arc min) for both light source and
photoreceptor.
8.3 Light Projector Source—The light source shall be a
9.1.1.4 0.333° (20 arc min) for both light source and
projector type capable of uniformly illuminating the specimen
photoreceptor.
withappropriatereflectorandlensestoprovideilluminationo
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