ASTM E809-94a(2000)

Designation: E 809 – 94a (Reapproved 2000)
Standard Practice for
Measuring Photometric Characteristics of Retroreflectors
This standard is issued under the fixed designation E 809; 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 (e) indicates an editorial change since the last revision or reapproval.
R 5 R /l
1. Scope
M I
3.2.2 coeffıcient of luminous intensity, R , n—of a retrore-
1.1 This practice describes the general procedures for in-
I
strumental measurement of the photometric characteristics of flector, ratio of the luminous intensity (I) of the retroreflector in
the direction of observation to the illuminance (E )atthe
retroreflective materials and retroreflective devices.
’
1.2 This practice is a comprehensive guide to the photom- retroreflector on a plane perpendicular to the direction of the
−1
incident light, expressed in candelas per lux (cd·lux ). R =(I/
etry of retroreflectors but does not include geometric terms that
I
are described in Practice E 808. E ).
’
1.3 This practice describes the parameters that are required 3.2.2.1 Discussion—Also called “coefficient of (retrore-
when stating photometric measurements in specific tests and flected) luminous intensity.” Recommended for determining
specifications for retroreflectors. the performance of retroreflectors such as button reflectors,
delineators, or automotive reflectors, since it depends on a unit
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the device and the area is not required. CIE uses the symbol R for
this quantity.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- 3.2.3 coeffıcient of retroreflected luminance, R , n—ratio of
L
the luminance, L, of a projected surface to the normal illumi-
bility of regulatory limitations prior to use.
nance, E , at the surface on a plane normal to the incident
’
2. Referenced Documents
light, expressed in candelas per square metre per lux
−2 −1
2.1 ASTM Standards: (cd·m ·lx ).
E 284 Terminology of Appearance
R 5 ~L/E !
L ’
E 308 Practice for Computing the Colors of Objects by
2 3.2.4 coeffıcient of (retroreflected) luminous flux, R , n—the
F
Using the CIE System
ratio of the flux per unit solid angle F8/V8 coming from the
E 808 Practice for Describing Retroreflection
retroreflector measured at the observation point to the total flux
2.2 CIE Documents:
(F) incident on the effective retroreflective surface, expressed
CIE Publication No. 54—Retroreflection—Definition and
−1
in candelas per lumen (cd·lm ).
Measurement
R 5 ~F8/V8!/F5 I/F5 R /cos b
CIE Publication No. 17.4—International Lighting Vocabu- F A
lary
3.2.4.1 Discussion—The units for this photometric quantity,
candelas per lumen, are sometimes abbreviated as CPL.
3. Terminology
3.2.5 coeffıcient of retroreflection, R , n—of a plane ret-
A
3.1 Terms and definitions in Terminology E 284 are appli-
roreflecting surface, the ratio of the coefficient of luminous
cable to this practice. In general, the terminology in this
intensity (R ) of a plane retroreflecting surface to its area (A)
I
−1 −2
practice agrees with that in CIE Publications 17.4 and 54.
expressed in candelas per lux per square metre (cd·lx ·m ).
3.2 Definitions:
R 5 R /A!
~
A I
3.2.1 coeffıcient of line retroreflection, R , of a retroreflect-
M
3.2.5.1 Discussion—The equivalent inch-pound units for
ing stripe, n—the ratio of the coefficient of luminous intensity
coefficient of retroreflection are candelas per foot candle per
( R ) of a retroreflecting stripe to its length (l), expressed in
I
−1 −1
square foot. The SI and inch-pound units are numerically
candelas per lux per metre (cd·lx ·m ).
equal. An equivalent term used for coefficient of retroreflection
is specific intensity per unit area, with symbol SIA or the CIE
This practice is under the jurisdiction of ASTM Committee E12 on Color and
symbol R8. The term coefficient of retroreflection and the
Appearance and is the direct responsibility of Subcommittee E12.10 on Retrore-
symbol R along with the SI units of candelas per lux per
A
flection.
square meter are recommended by ASTM.
Current edition approved April 15, 1994. Published June 1994. Originally
published as E 809 – 81. Last previous edition E 809 – 94. 3.2.6 datum mark, n—in retroreflection, an indication on the
Annual Book of ASTM Standards, Vol 06.01.
Available from USNC/CIE Publications Office; TLA Lighting Consultants,
Inc., 77 Pond St., Salem, MA 01970.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 809
retroreflector that is used to define the orientation of the near its exposed surface (for example, retroreflective sheeting,
retroreflector with respect to rotation about the retroreflector beaded paint, highway sign surfaces, or pavement striping).
axis. 3.2.19 retroreflective sheeting, n—a retroreflective material
3.2.6.1 Discussion—The datum mark must not lie on the preassembled as a thin film ready for use.
3.2.20 retroreflector, n—a reflecting surface or device from
retroreflector axis.
3.2.7 entrance angle, b, n— in retroreflection, angle be- which, when directionally irradiated, the reflected rays are
preferentially returned in directions close to the opposite of the
tween the illumination axis and the retroreflector axis.
3.2.7.1 Discussion—The entrance angle is usually no larger direction of the incident rays, this property being maintained
over wide variations of the direction of the incident rays. [CIE,
than 90°, but for completeness its full range is defined as 0° #
B
b # 180°. To completely specify the orientation, this angle is 1982]
3.2.21 retroreflector axis, n—a designated line segment
characterized by two components, b and b . The first axis is
1 2
an axis through the retroreflector center and perpendicular to from the retroreflector center that is used to describe the
angular position of the retroreflector.
the observation half plane. The first component of the entrance
angle (b ) is the angle from the illumination axis to the plane 3.2.21.1 Discussion—The direction of the retroreflector axis
is usually chosen centrally among the intended directions of
containing the retroreflector axis and the first axis. The second
component of the entrance angle (b ) is the angle from the illumination; for example, the direction of the road on which or
with respect to which the retroreflector is intended to be
plane containing the observation half plane to the retroreflector
axis. The second axis is an axis through the retroreflector center positioned. In testing horizontal road markings the retroreflec-
tor axis is usually the normal to the test surface.
and perpendicular to both the first axis and the retroreflector
3.2.22 retroreflector center, n—a point on or near a retrore-
axis. The positive direction of the second axis lies in the
flector that is designated to be the center of the device for the
observation half plane.
purpose of specifying its performance.
3.2.8 goniometer—an instrument for measuring or setting
3.2.23 rotation angle, e, n— in retroreflection, angle indi-
angles.
cating the orientation of the specimen when it is rotated about
3.2.9 illuminance, E—E, E , n—luminous flux incident per
v
the retroreflector axis.
unit of area.
3.2.23.1 Discussion—The rotation angle is the dihedral
3.2.10 illumination axis, n— in retroreflection, a line from
angle from the half-plane originating on the retroreflector axis
the effective center of the source aperture to the retroreflector
and containing the positive part of the second axis to the half
center.
plane originating on the retroreflector axis and containing the
3.2.11 observation angle, n—angle between the axes of the
datum mark. Range: −180° # e # 180°.
incident beam and the observed (reflected) beam, ( in retrore-
3.2.24 viewing angle, n, n— in retroreflection, the angle
flection, a, between the illumination axis and the observation
between the retroreflector axis and the observation axis.
axis).
3.3 Definitions of Terms Specific to This Standard:
3.2.12 observation axis, n— in retroreflection, a line from
3.3.1 normal illuminance, E — the illuminance on a ret-
the centroid of the effective receiver aperture to the retrore- ’
roreflective surface measured in the plane which passes
flector center.
through the retroreflector center and is perpendicular to the axis
3.2.13 photometer—an instrument for measuring light.
of incident light (illumination axis).
3.2.14 retroreflectance factor, R , n—of a plane retroreflect-
F
3.3.1.1 Discussion—In SI units, normal illuminance is mea-
ing surface, the dimensionless ratio of the coefficient of
-2
sured in lux (lumens·m ).
luminous intensity (R ) of a plane retroreflecting surface having
I
3.3.2 photopic receiver—a receiver of radiation with a
area A to the coefficient of luminous intensity of a perfect
spectral responsivity which conforms to the V (l) distribution
reflecting diffuser of the same area under the same conditions
of the CIE Photopic Standard Observer that is specified in
of illumination and observation.
Method E 308.
R 5 R /A cosb3 cos n
F I
3.3.3 reflected illuminance, E —illuminance at the receiver
r
3.2.14.1 Discussion—In the above expression b is the
measured on a plane perpendicular to the observation axis.
entrance angle and n is the viewing angle. The quantity, R ,is
F
3.3.3.1 Discussion—This quantity is used in the calculation
numerically the same as the reflectance factor, R.
of the coefficient of luminous intensity, R : R =(I/
I
I
3.2.15 retroreflection, n—reflection in which the reflected
E )=(E d )/E , where d is the distance from the retroreflec-
’ r ’
rays are preferentially returned in directions close to the
tor to the receptor.
opposite of the direction of the incident rays, this property
4. Summary of Practice
being maintained over wide variations of the direction of the
B
incident rays. [CIE]
4.1 The fundamental procedure described in this practice
3.2.16 retroreflective device, n—deprecated term; use ret- involves measurements of retroreflection based on the ratio of
roreflector.
the retroreflected illuminance at the observation position to the
3.2.17 retroreflective element, n—a single optical unit incident illuminance measured perpendicular to the illumina-
which by refraction or reflection, or both, produces the tion axis at the retroreflector. From these measurements, along
phenomenon of retroreflection. with the geometry of test, various photometric quantities
3.2.18 retroreflective material, n—a material that has a thin applicable to retroreflectors can be determined.
continuous layer of small retroreflective elements on or very 4.2 Also described are methods of comparative testing
E 809
where unknown specimens are measured relative to an agreed- flectors, items in paragraphs 7.1.1-7.1.12 must be included.
upon standard retroreflector (a substitutional test method). Refer to Fig. 1 for a simplified diagram of measurement
geometry terminology.
5. Significance and Use
7.1.1 Retroreflective photometric quantity, such as: coeffi-
5.1 This practice describes procedures used to measure
cient of luminous intensity (R ), coefficient of retroreflected
I
photometric quantities that relate to the visual perception of
luminance (R ) (also called specific luminance), coefficient of
L
retroreflected light. The most significant usage is in the relation
retroreflection (R ), coefficient of line retroreflection (R ),
A M
to the nighttime vehicle headlamp, retroreflector, and driver’s
reflectance factor (R ), or coefficient of luminous flux per unit
F
eye geometry. For this reason the CIE Standard Source A is
solid angle (R ).
F
used to represent a tungsten vehicle headlamp and the receptor
7.1.1.1 In specifications, a minimum acceptable quantitative
has the photopic, V (l), spectral responsivity corresponding to
value is usually established.
the light adapted human eye. Although the geometry must be
7.1.2 Units in which each quantity is to be measured (for
specified by the user, it will, in general, correspond to the −1 −2
example cd·lx ·m ).
relation between the vehicle headlamp, the retroreflector, and
7.1.3 Observation angle.
the vehicle driver’s eye position.
7.1.4 Entrance angle. When specifying an entrance angle
6. Uses and Applications
near 0°, care must be taken to prevent specular reflection from
entering the photoreceptor.
6.1 Coeffıcient of Retroreflection— This quantity is used to
7.1.5 Components of the entrance angle (b andb ), which
specify the performance of retroreflective sheeting. It considers 1 2
shall be specified if the entrance angle is other than 0°.
the retroreflector as an apparent point source whose retrore-
7.1.6 Rotation angle and the datum mark position shall be
flected luminous intensity is dependent on the area of the
specified if random rotational orientation of the test specimen
retroreflective surface involved. It is a useful engineering
is not suitable.
quantity for determining the photometric performance of such
7.1.7 Test distance or minimum test distance.
retroreflective surfaces as highway delineators or warning
7.1.8 Test specimen size and shape.
devices. The coefficient of retroreflection may also be used to
7.1.9 Photoreceptor angular aperture.
determine the minimum area of retroreflective sheeting neces-
7.1.10 Source angular aperture.
sary for a desired level of photometric performance.
7.1.11 Retroreflector center.
6.2 Coeffıcient of Line Retroreflection (of a Reflecting
7.1.12 Retroreflector axis. The retroreflector axis is usually
Stripe)—This term may be used to describe the retroreflective
perpendicular to the surface of retroreflective sheeting. In such
performance of long narrow strips of retroreflective materials,
complex devices as automobile or bicycle reflectors, the
when the actual width is not as important as is the reflectivity
retroreflector axis and retroreflector center may be defined with
per unit length.
respect to the illumination direction.
6.3 Reflectance Factor (of a Plane Reflecting Surface)—
This is a useful term for comparing surfaces specifically
8. Apparatus
designed for retroreflection to surfaces which are generally
8.1 General—The apparatus shall consist of a photorecep-
considered to be diffuse reflectors. Since almost all natural
tor, a light projector source, a specimen goniometer, an
surfaces tend to retroreflect slightly, materials such as BaSO
observer goniometer, and a photometric range.
can have a reflectance factor much higher than one (as much as
8.2 Photoreceptor—The photoreceptor shall be equipped as
four) at small observation angles. Such diffuse reflectance
follows:
standards should be used for calibration only at large observa-
8.2.1 Photopic Filter—The photoreceptor shall be equipped
tion angles, for exam
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