ASTM E808-99a
(Practice)Standard Practice for Describing Retroreflection
Standard Practice for Describing Retroreflection
SCOPE
1.1 This practice provides terminology, alternative geometrical coordinate systems, and procedures for designating angles in descriptions of retroreflectors, specifications for retroreflector performance, and measurements of retroreflection.
1.2 Terminology defined herein includes terms germane to other ASTM documents on retroreflection.
1.3 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: E 808 – 99a
Standard Practice for
Describing Retroreflection
This standard is issued under the fixed designation E 808; 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.
photopic observer. Analogous terms for other purposes can be defined by
1. Scope
using appropriate spectral weighting.
1.1 This practice provides terminology, alternative geo-
3.2 Definitions: The delimiting phrase “in retroreflection”
metrical coordinate systems, and procedures for designating
applies to each of the following definitions when used outside
angles in descriptions of retroreflectors, specifications for
the context of this or other retroreflection standards.
retroreflector performance, and measurements of retroreflec-
3.2.1 coeffıcient of line retroreflection, R , n—of a retrore-
tion. M
flecting stripe, the ratio of the coefficient of luminous intensity
1.2 Terminology defined herein includes terms germane to
(R ) to the length (l), expressed in candelas per lux per metre
other ASTM documents on retroreflection. I
–1 –1
(cd·lx ·m ). R = R /l.
1.3 This standard does not purport to address all of the M I
3.2.1.1 Discussion—R depends on the spectral composi-
safety concerns, if any, associated with its use. It is the M
tion of the illumination which is usually CIE illuminant A.
responsibility of the user of this standard to establish appro-
3.2.2 coeffıcient of luminous intensity, R , n—of a retrore-
priate safety and health practices and determine the applica- I
flector, ratio of the luminous intensity (I) of the retroreflector in
bility of regulatory limitations prior to use.
the direction of observation to the illuminance (E )atthe
’
2. Referenced Documents
retroreflector on a plane perpendicular to the direction of the
–1
incident light, expressed in candelas per lux (cd·lx ). R =
2.1 ASTM Standards:
I
(I/E ).
E 284 Terminology of Appearance
’
3.2.2.1 Discussion—In a given measurement one obtains
2.2 Federal Standard:
the average R over the solid angles of incidence and viewing
Fed. Std. No. 370 Instrumental Photometric Measurements
I
subtended by the source and receiver apertures, respectively. In
of Retroreflecting Materials and Retroreflecting Devices
practice, I is often determined as the product of the illuminance
2.3 CIE Document:
at the observer and the distance squared (I=E d ). R depends
CIE Publication No. 54, Retroreflection-Definition and
r I
on the spectral composition of the illumination which is usually
Measurement
CIE illuminant A.
3. Terminology
3.2.2.2 Discussion—Also called coeffıcient of (retrore-
flected) luminous intensity. Equivalent commonly used terms
3.1 Terms and definitions in Terminology E 284 are appli-
are CIL and SI (specific intensity). CIE Publication 54 uses the
cable to this standard.
symbol R for R . The ASTM recommendation is to use the
3.1.1 In accordance with the convention appearing in the
I
symbol R .
Significance and Use section of Terminology E 284, the
I
3.2.3 coeffıcient of retroreflected luminance, R , n—the
superscript B appearing after [CIE] at the end of a definition
L
ratio of the luminance, L, in the direction of observation to the
indicates that the given definition is a modification of that cited
normal illuminance, E , at the surface on a plane normal to the
with little difference in essential meaning.
’
incident light, expressed in candelas per square metre per lux
–2
NOTE 1—The terminology given here describes visual observation of
–1
[(cd·m )·lx ].
luminance as defined by the CIE V (l) spectral weighting function for the
R 5 ~L/E ! 5 ~R /A cos n! 5 ~I/EA cos n! 5 ~R / cos n! (1)
L ’ I A
where:
This practice is under the jurisdiction of ASTM Committee E-12 on Color and
A = surface area of the sample, and
Appearance and is the direct responsibility of Subcommittee E12.10 on Retrore-
n = viewing angle.
flection.
3.2.3.1 Discussion—The units millicandela per square me-
Current edition approved Feb. 10, 1999. Published April 1999. Originally
–2 –1
published as E 808-81. Last previous edition E 808-99.
tre per lux [(mcd·m )·lx ] are usually used to express the R
L
Annual Book of ASTM Standards, Vol 06.01.
values of road marking surfaces. This quantity is also referred
Available from Standardization Documents Order Desk, Bldg. 4 Ave., Phila-
to as specific luminance. Historically the symbol SL was used
delphia, PA 19111-5094, Attn: NPODS.
Available from USNC/CIE Publications Office, TLA Lighting Consultants, for R . In some references CRL is used. These are all
L
Inc., 7 Pond St., Salem, MA 01970.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 808
equivalent, but R is preferred. two components b and b . Since by definition b is always
L 1 2
positive, the common practice of referring to the small entrance
3.2.3.2 Discussion—R depends on the spectral composi-
L
tion of the illumination which is usually CIE illuminant A. angles that direct specular reflections away from the photore-
ceptor as negative valued is deprecated by ASTM. The
3.2.4 coeffıcient of (retroreflected) luminous flux, R , n—the
F
ratio of the luminous flux per unit solid angle, F8/V8,inthe recommendation is to designate such negative values as
belonging to b .
direction of observation to the total flux F incident on the
effective retroreflective surface, expressed in candelas per 3.2.12 entrance angle component, b , n—the angle from the
–1
lumen (cd·lm ). illumination axis to the plane containing the retroreflector axis
and the first axis. Range: –180°
R 5 ~F8/V8!/F5 I/F5 R /cos b (2)
F A
3.2.13 entrance angle component, b , n—the angle from the
3.2.4.1 Discussion—The units for this photometric quantity,
plane containing the observation half-plane to the retroreflector
candelas per lumen, are sometimes abbreviated as CPL.
axis. Range: –90°#b #90°.
3.2.4.2 Discussion—R depends on the spectral composi-
F
3.2.13.1 Discussion—For some measurements it is conve-
tion of the illumination which is usually CIE illuminant A.
nient to extend the range of b to –180°
2 2 1
3.2.5 coeffıcient of retroreflection, R , n—of a plane ret-
A
then be restricted to –90°
roreflecting surface, the ratio of the coefficient of luminous
3.2.14 entrance half-plane, n—the half-plane that originates
intensity (R ) to the area (A), expressed in candelas per lux per
I
on the line of the illumination axis and contains the retrore-
–1 –2
square metre (cd·lx ·m ). R = R /A.
A I
flector axis.
3.2.5.1 Discussion—The equivalent inch-pound units for
3.2.15 first axis, n—the axis through the retroreflector
coefficient of retroreflection are candelas per foot candle per
center and perpendicular to the observation half-plane.
square foot. The SI and inch-pound units are numerically
3.2.16 fractional retroreflectance, R , n—the fraction of
T
equal, because the units of R reduce to 1/sr. An equivalent
A
unidirectional flux illuminating a retroreflector that is received
term used for coefficient of retroreflection is specific intensity
at observation angles less than a designated value, a .
max
per unit area, with symbol SIA or the CIE symbol R8. The term
3.2.16.1 Discussion—R has no meaning unless a is
T max
coefficient of retroreflection and the symbol R along with the
A
specified.
SI units of candelas per lux per square metre are recommended
3.2.16.2 Discussion—For a flat retroreflector R may be
T
by ASTM.
calculated as follows:
3.2.5.2 Discussion—The radiometric BRDF is not the ana-
a p R ~a,r!
max
A
logue of R but rather of R .
A F a dadr. (3)
* *
cosb
a50 r5–p
3.2.5.3 Discussion—R depends on the spectral composi-
A
tion of the illumination which is usually CIE illuminant A. For a non-flat retroreflector R may be calculated as follows:
T
3.2.6 co-entrance angle, e, n—the complement of the angle a p R ~a,r!
max
I
a dadr. (4)
* *
A
between the retroreflector axis and the illumination axis. a50 r5–p
P
A is the area of the retroreflector as projected in the direction of
3.2.6.1 Discussion—e=90°-b. Range 0°
illumination. Angles b and v must remain fixed through the integra-
s
zontal road markings, the retroreflector axis is considered to be
tion. Angles a and r are in radians: R is unitless. Presentation angle g
T
the normal to the road surface, making e the angle of
may replace r in these formulas. For very small values of b, rotation
inclination of the illumination axis over the road surface.
angle e may replace r in these formulas. For example, for b=5° the
3.2.7 co-viewing angle, a, n—the complement of the angle
resulting error will be less than, usually much less than, 0.5 % of the
between the retroreflector axis and the observation axis. calculated R .
T
3.2.7.1 Discussion—a= 90°-n. Range 0°
3.2.16.3 Discussion—R is usually expressed in percent.
T
zontal road markings, the retroreflector axis is considered to be
3.2.17 illumination axis, n—the half-line from the retrore-
the normal to the road surface, making a the angle of
flector center through the source point.
inclination of the observation axis over the road surface.
3.2.18 illumination distance, n—the distance between the
3.2.8 datum axis, n—a designated half-line from the retrore-
source point and the retroreflector center.
flector center perpendicular to the retroreflector axis.
3.2.19 observation angle, a, n—the angle between the
3.2.8.1 Discussion—The datum axis together with the ret-
illumination axis and the observation axis.
roreflector center and the retroreflector axis establish the
3.2.19.1 Discussion—The observation angle is never nega-
position of the retroreflector.
tive and is almost always less than 10° and usually no more
3.2.9 datum mark, n—an indication on the retroreflector, off
than 2°. The full range is defined as 0°#a<180°.
the retroreflector axis, that establishes the direction of the
3.2.20 observation axis, n—the half-line from the retrore-
datum axis.
flector center through the observation point.
3.2.10 datum half-plane, n—the half-plane that originates 3.2.21 observation distance, d, n—the distance between the
on the line of the retroreflector axis and contains the datum
retroreflector center and the observation point.
axis. 3.2.22 observation half-plane, n—the half-plane that origi-
3.2.11 entrance angle, b, n—the angle between the illumi- nates on the line of the illumination axis and contains the
nation axis and the retroreflector axis. observation axis.
3.2.11.1 Discussion—The entrance angle is usually no 3.2.23 observation point, n—the point taken as the location
larger than 90°, but for completeness its full range is defined as of the receiver.
0°#b#180°. In the CIE (goniometer) system b is resolved into 3.2.23.1 Discussion—in real systems the receiver has finite
E 808
size and the observation point is typically the center of the usually coincides with the axis of symmetry of the retroreflec-
entrance pupil. tor. For horizontal road markings the normal to the surface is
3.2.24 orientation angle, v , n—the angle in a plane per- chosen as the retroreflector axis.
s
pendicular to the retroreflector axis from the entrance half- 3.2.34 retroreflector center, n—the point on or near a
plane to the datum axis, measured counter-clockwise from the retroreflector that is designated to be the location of the device.
viewpoint of the source.
3.2.35 rho angle, r, n—the dihedral angle from the obser-
3.2.24.1 Discussion—Range –180°
vation half-plane to the half-plane that originates on the line of
s
ous editions of Practice E 808 as well as in CIE Pub. 54, 1982, the illumination axis and contains the datum axis, measured
orientation angle is defined as v, the supplement of the above
counter-clockwise from the viewpoint of the source.
defined orientation angle v . The change reverses the sense of
3.2.35.1 Discussion—Range –180°
s
orientation angle, making it now agree with the counterclock-
3.2.36 RM azimuthal angle, b, n—the dihedral angle from
wise sense of rotation angle, e, and exchanges the 0° and 180°
the half-plane originating on the line of the retroreflector axis
points, making it now agree with Fed. Std. No. 370, §2.2.9b.
and containing the obverse of the illumination axis to the
3.2.25 presentation angle, g, n—the dihedral angle from the
half-plane originating on the line of the retroreflector axis and
entrance half-plane to the observation half-plane, measured
containing the observation axis, measured clockwise from a
counter-clockwise from the viewpoint of the source.
viewpoint on the retroreflector axis.
3.2.25.1 Discussion—Range –180°
3.2.36.1 Discussion—Range –180°
3.2.26 retroreflectance factor, R , (of a plane retroreflecting
F
3.2.37 RM supplemental azimuthal angle, d, n— the angle
surface), n—the dimensionless ratio of the coefficient of
in a plane perpendicular to the retroreflector axis from the
luminous intensity (R ) of a plane retroreflecting surface
I
obverse of the datum axis to the half-plane that originates on
having area A to the coefficient of luminous intensity of a
the line of the retroreflector axis and contains the observation
perfect reflecting diffuser of the same area under the same
axis, measured clockwise from a viewpoint on the retroreflec-
conditions of illumination and observation.
tor axis.
p R 3.2.37.1 Discussion—Range –180°
I
R 5 (5)
F
A cos b cos n
3.2.38 rotation angle, e,n—the angle in a plane perpen-
dicular to the retroreflector axis from the observation half-
3.2.26.1 Discussion—In the above expression b is the
plane to the datum axis, measured counter-clockwise from a
entrance angle and n is the viewing angle. The quantity, R ,is
F
viewpoint on the retroreflector axis.
numerically the same as the reflectance factor, R.
3.2.38.1 Discussion—Range– 180°
3.2.26.2 Discussion—R depends on the spectral composi-
F
is applicable when entrance angle and viewing angle are less
tion of the illumination which is usually CIE illuminant A.
than 90°. More generally, rotation angle is the angle from the
3.2.27 retroreflection, n—reflection in which reflected rays
positive part of second axis to the datum axis, measured
are preferentially returned in directions close to the opposite of
counterclockwise from a viewpoint on the retroreflector axis.
the direction of the incident rays, this property being main-
3.2.38.2 Discussion—Rotation of the sample about the ret-
tained over wide variations of the direction of the incident rays.
B
roreflector axis while the source
...
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