ASTM E2540-08
(Test Method)Standard Test Method for Measurement of Retroreflective Signs Using a Portable Retroreflectometer at a 0.5 Degree Observation Angle
Standard Test Method for Measurement of Retroreflective Signs Using a Portable Retroreflectometer at a 0.5 Degree Observation Angle
SIGNIFICANCE AND USE
Measurements made by this test method are related to the night time brightness of retroreflective traffic signs approximately facing the driver of a mid-sized automobile equipped with tungsten filament headlights at about 100 m distance.
Retroreflective material used on traffic signs degrades with time and requires periodic measurement to ensure that the performance of the retroflection provides adequate safety to the driver.
The quality of the sign as to material used, age, and wear pattern will have an effect on the coefficient of retroreflection. These conditions need to be observed and noted by the user.
This test method is not intended for use for the measurement of signs when the instrument entrance and observation angles differ from those specified herein.
SCOPE
1.1 This test method covers measurement of the retroreflective properties of sign materials such as traffic signs and symbols (vertical surfaces) using a portable retroreflectometer that can be used in the field. The portable retroreflectometer is a hand-held instrument with a defined standard geometry that can be placed in contact with sign material to measure the retroreflection in a standard geometry. The measurements can be compared to minimum requirements to determine the need for replacement. Entrance and observation angles specified in this test method are those used currently in the United States and may differ from the angles used elsewhere in the world.
1.2 This test method is intended to be used for the field measurement of traffic signs but may be used to measure the performance of materials before placing the sign in the field or before placing the sign material on the sign face.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
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:E2540 −08
Standard Test Method for
Measurement of Retroreflective Signs Using a Portable
Retroreflectometer at a 0.5 Degree Observation Angle
This standard is issued under the fixed designation E2540; 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.
1. Scope Retroreflective Sheeting Utilizing the Coplanar Geometry
1.1 This test method covers measurement of the retroreflec-
3. Terminology
tive properties of sign materials such as traffic signs and
3.1 The terminology used in this test method generally
symbols (vertical surfaces) using a portable retroreflectometer
agrees with that used in Terminology E284.
that can be used in the field. The portable retroreflectometer is
a hand-held instrument with a defined standard geometry that
3.2 Definitions—The delimiting phrase “in retroreflection”
can be placed in contact with sign material to measure the
applies to each of the following definitions when used outside
retroreflection in a standard geometry. The measurements can
the context of this or other retroreflection standards.
be compared to minimum requirements to determine the need
3.2.1 annular geometry, n—the portable instrument retrore-
for replacement. Entrance and observation angles specified in
flection collection method where the retroreflected lux is
this test method are those used currently in the United States
collected in an annulus 0.1 degrees wide centered on the
and may differ from the angles used elsewhere in the world.
illumination axis.
3.2.1.1 Discussion—The angle measured from the illumina-
1.2 This test method is intended to be used for the field
tion axis to the circle which divides the annulus into equal
measurement of traffic signs but may be used to measure the
areas corresponds to a specific observation angle.
performance of materials before placing the sign in the field or
before placing the sign material on the sign face.
3.2.2 coeffıcient of retroreflection, R , n—of a plane retrore-
A
flecting surface, the ratio of the coefficient of luminous
1.3 The values stated in SI units are to be regarded as
intensity (R ) of a plane retroreflecting surface to its area (A),
standard. No other units of measurement are included in this I
–1 –2
expressed in candelas per lux per square metre (cd · lx ·m ).
standard.
3.2.3 datum axis, n—a designated half-line from the retrore-
1.4 This standard does not purport to address all of the
flector center perpendicular to the retroreflector axis.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3.2.4 entrance angle, β,n—the angle between the illumina-
priate safety and health practices and determine the applica-
tion axis and the retroreflector axis.
bility of regulatory limitations prior to use.
3.2.5 entrance half-plane, n—the half plane that originates
on the line of the illumination axis and contains the retrore-
2. Referenced Documents
flector axis.
2.1 ASTM Standards:
3.2.6 instrument standard, n—working standard used to
E284 Terminology of Appearance
standardize the portable retroreflectometer.
E808 Practice for Describing Retroreflection
3.2.7 observation angle, α,n—the angle between the illu-
E809 Practice for Measuring Photometric Characteristics of
mination axis and the observation axis.
Retroreflectors
3.2.8 observation half-plane, n—the half plane that origi-
E810 Test Method for Coefficient of Retroreflection of
nates on the line of the illumination axis and contains the
observation axis.
This test method is under the jurisdiction of ASTM Committee E12 on Color 3.2.9 orientation angle, ω,n—the angle in a plane perpen-
s
and Appearance and is the direct responsibility of Subcommittee E12.10 on
dicular to the retroreflector axis from the entrance half-plane to
Retroreflection.
the datum axis, measured counter-clockwise from the view-
Current edition approved April 15, 2008. Published May 2008. DOI: 10.1520/
point of the source.
E2540-08.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.2.10 portable retroreflectometer, n—a hand-held instru-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ment that can be used in the field or in the laboratory for
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. measurement of retroreflectance.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2540−08
3.2.10.1 Discussion—In this test method, “portable retrore- 6. Apparatus
flectometer”referstoahand-heldinstrumentthatcanbeplaced
6.1 Portable Retroreflectometer—The retroreflectometer
in contact with sign material to measure the retroreflection in a
shall be portable, with the capability of being placed at various
standard geometry.
locations on the signs. The retroreflectometer shall be con-
3.2.11 presentation angle, γ,n—the dihedral angle from the
structed so that placement on the sign will preclude stray light
entrance half-plane to the observation half-plane, measured
(daylight) from entering the measurement area of the instru-
counter-clockwise from the viewpoint of the source.
ment and affecting the reading.
3.2.12 retroreflection, n—a reflection in which the reflected
6.2 Instrument Standard, or standards of desired color(s)
rays are returned preferentially in directions close to the
and material(s).
opposite of the direction of the incident rays, this property
6.3 Light Source Requirements:
being maintained over wide variations of the direction of the
incident rays.
6.3.1 The projection optics shall be such that the illumi-
nance at any point over the measurement area shall be within
3.2.13 rotation angle,ε,n—the angle in a plane perpendicu-
10 % of the average illuminance.
lar to the retroreflector axis from the observation half-plane to
the datum axis, measured counter-clockwise from the view- 6.3.2 The aperture angle of the source as determined from
the center of the measurement area shall be not greater than
point of the source.
0.1°.
3.3 Definitions of entrance angle components β and β,as
1 2
well as other geometrical terms undefined in this test method,
6.4 Receiver Requirements:
may be found in Practice E808.
6.4.1 The receiver shall have sufficient sensitivity and range
to accommodate coefficient of retroreflection values from 0.1
–1 –2
4. Summary of Test Method
to 1999.9 cd · lx ·m .
4.1 This test method involves the use of commercial 6.4.2 The combined spectral distribution of the light source
portable retroreflectometers for determining the retroreflectiv- and the spectral responsivity of the receiver shall match the
ity of highway signing materials. combined spectral distribution of CIE Illuminant A and the
V(λ) spectral luminous efficiency function according to the
4.2 The entrance angle shall be 4°.
following criterion: For any choice of plano-parallel colored
4.3 The observation angle shall be 0.5°.
absorptive filter mounted in front of a white retroreflective
sample, the ratio of the R measured with the filter to the R
4.4 The portable retroreflectometer uses an instrument
A A
measured without the filter shall be within 10 % of the
standard for standardization.
Illuminant A luminous transmittance of an air spaced pair of
4.5 After standardization, the retroreflectometer is placed in
two such filters.
contactwiththesigntobetested,ensuringthatonlythedesired
6.4.3 The instrument may be either an instrument with point
portion of the sign is within the measurement area of the
geometry, a “point instrument,” or an instrument with annular
instrument.
geometry, an “annular instrument,” depending on the shape of
4.6 The reading displayed by the retroreflectometer is
thereceiveraperture(seeFig.1).Pointandannularinstruments
recorded. The retroreflectometer is then moved to another
make geometrically different measurements of R , which may
A
position on the sign, and this value is recorded.Aminimum of
produce values differing on the order of 10 %. Both measure-
four readings shall be taken and averaged for each retroreflec-
ments are valid for most purposes, but the user should learn the
tive color on the sign to be tested.
type of instrument from its specifications sheet and be aware of
certain differences in operation and interpretation. For both
5. Significance and Use
instrument types, the “up” position of the instrument shall be
known. Both types of instruments may make additional mea-
5.1 Measurements made by this test method are related to
thenighttimebrightnessofretroreflectivetrafficsignsapproxi- surements at observation angles other than the 0.5 degree of
this specification and combine the measurement at two or more
mately facing the driver of a mid-sized automobile equipped
with tungsten filament headlights at about 100 m distance. different observation angles if the readings at the different
observation angles are reported separately.
5.2 Retroreflective material used on traffic signs degrades
6.4.3.1 The point instrument makes an R measurement
with time and requires periodic measurement to ensure that the A
with the source and receiver geometry virtually identical to an
performanceoftheretroflectionprovidesadequatesafetytothe
R measurement made on a range instrument following the
driver. A
procedure of Test Method E810. The 4° entrance angle would
5.3 The quality of the sign as to material used, age, and
be set on a range instrument by setting β =–4°; β =0°. This
1 2
wear pattern will have an effect on the coefficient of retrore-
may be called “–4° entrance angle.” The rotation angle (ε) for
flection.Theseconditionsneedtobeobservedandnotedbythe
the point instrument is determined by the angular position of
user.
the instrument on the sign face. Assuming the retroreflector’s
5.4 This test method is not intended for use for the mea- datum axis to be upward, the rotation angle equals 0° when the
surement of signs when the instrument entrance and observa- instrument is upright. Clockwise rotation of the instrument on
tion angles differ from those specified herein. the sign face increases the rotation angle.
E2540−08
FIG. 1Annular and Point Aperture Instrument Angles
ment would include the β and β settings indicated in Table 1.
1 2
There is no definite rotation angle (ε) for the annular instru-
ment. All values from –180° to +180° are included in the
measurement.
6.4.3.4 Fortheannularinstrumentthe“up”markingshallbe
opposite the entrance half-plane (see Fig. 2).
6.4.3.5 For both instrument types, the orientation angle (ω )
s
is determined by the angular position of the instrument on the
sign face. It is the rotation angle (ε) rather than the orientation
angle (ω ) which primarily affects retroreflection of signs
s
measured at the small 4° entrance angle.
6.4.3.6 Rotationally insensitive sheetings, such as glass
bead sheetings, have R values that are nearly independent of
A
TABLE 1 Laboratory Emulation of Annular Instrument Geometry
αβ β ε
1 2
0.5° 3.86° −1.03° −165°
0.5° 3.47° −2.00° −150°
0.5° 2.83° −2.83° −135°
0.5° 2.00° −3.46° −120°
0.5° 1.04° −3.86° −105°
0.5° 0.00° −4.00° −90°
0.5° −1.04° −3.86° −75°
0.5° −2.00° −3.46° −60°
0.5° −2.83° −2.83° −45°
0.5° −3.47° −2.00° −30°
0.5° −3.86° −1.03° −15°
NOTE 1—For each instrument type, the illumination beam is 4°
0.5° −4.00° 0.00° 0°
downward. For the point instrument, receiver is above source.
0.5° −3.86° 1.03° 15°
FIG. 2Upright Optical Schematics
0.5° −3.47° 2.00° 30°
0.5° −2.83° 2.83° 45°
0.5° −2.00° 3.46° 60°
6.4.3.2 For the point instrument the “up” marking shall be 0.5° −1.04° 3.86° 75°
0.5° 0.00° 4.00° 90°
opposite the entrance half-plane. It shall be in the observation
0.5° 1.04° 3.86° 105°
half-plane (see Fig. 2).
0.5° 2.00° 3.46° 120°
6.4.3.3 The annular instrument makes an R measurement 0.5° 2.83° 2.83° 135°
A
0.5° 3.47° 2.00° 150°
similar to an average of a great number of R measurements on
A
0.5° 3.86° 1.03° 165°
a range instrument with presentation angle (γ) varying between
0.5° 4.00° 0.00° 180°
–180° and +180°. For the 4° entrance angle the range instru-
E2540−08
the rotation angle. Accordingly, the point and annular instru- 7.1.1 Instrument standards are generally of glass-bead
ments will make practically identical measurements of R for sheeting construction. The glass-bead sheeting instrument
A
signs made with such sheetings. standard shall be calibrated in the laboratory range instrument
6.4.3.7 Most prismatic retroreflectors are rotationally at α=0.5°; β =–4°; β =0°; ε=0°. The glass-bead sheeting
1 2
sensitive, having R values that vary significantly with rotation standardmusthaveadatummarkforthecalibrationlaboratory,
A
angle (ε), even at small entrance angles. The difference of R but this mark is not required for its use with either type of
A
measurements made with the two types of instrument on instrument.
prismatic signs may become as great as 20 % in extreme cases,
7.1.2 If prismatic materials will be used as standards, they
but is generally on the order of 10 %. Neither the magnitude
shall be calibrated differently for the two types of instrument.
nor the direction of difference can be predicted for unknown
7.1.2.1 A prismatic standard for a point instrument shall be
samples. Thus, critical comparison of prismatic sign R values
A
calibrated following the procedure of Test Method E810.It
measured by instruments of the two types is not recommended.
shall be calibrated in the laboratory range instrument at
6.4.3.8 Apoint instrument can gage the variation of R with
A
α =0.5°; β =–4°; β =0°; ε=0°.
1 2
rotation angle by placing it with different angular positions
(a) The prismatic instrument standard must have a datum
upon the sign face. R variation of 5 % for 5° rotation is not
A
mark for the calibration laboratory, and this mark is required
unusual.Accordingly, repeatable R measurement of prismatic
A
for its use with the point instrument. The datum mark shall
signs with a point instrument, requires care in angular posi-
align with the “up” direction of the instrument.
tioning.
(b) Aprismatic standard for an annular instrument shall be
6.4.3.9 An annular instrument cannot gage the variation of
calibrated in the laboratory range instrument at the angles
R with rotation angle. Accordingly, repeatable R measure-
A A
given in Table 1. The calibration involves twenty-four R
A
ment of prismatic signs with an annular instrument does not
measurements, which values are then averaged to produce the
require care in angular p
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