ASTM E1709-16(2022)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation:E1709 −16 (Reapproved 2022)
Standard Test Method for
Measurement of Retroreflective Signs Using a Portable
Retroreflectometer at a 0.2 Degree Observation Angle
This standard is issued under the fixed designation E1709; 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 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers measurement of the retroreflec-
D4956Specification for Retroreflective Sheeting for Traffic
tive properties of sign materials such as traffic signs and
Control
symbols (vertical surfaces) using a portable retroreflectometer
E177Practice for Use of the Terms Precision and Bias in
that can be used in the field. The portable retroreflectometer is
ASTM Test Methods
a hand-held instrument with a defined standard geometry that
E284Terminology of Appearance
can be placed in contact with sign material to measure the
E691Practice for Conducting an Interlaboratory Study to
retroreflection in a standard geometry. The measurements can
Determine the Precision of a Test Method
be compared to minimum requirements to determine the need
E808Practice for Describing Retroreflection
for replacement. Entrance and observation angles specified in
E809Practice for Measuring Photometric Characteristics of
this test method are those used currently in the United States
Retroreflectors
and may differ from the angles used elsewhere in the world.
E810Test Method for Coefficient of Retroreflection of
1.2 This test method is intended to be used for the field
Retroreflective Sheeting Utilizing the Coplanar Geometry
measurement of traffic signs but may be used to measure the E2540Test Method for Measurement of Retroreflective
Signs Using a Portable Retroreflectometer at a 0.5 Degree
performance of materials before placing the sign in the field or
Observation Angle
before placing the sign material on the sign face.
1.3 This test method covers measurements at a 0.2 degree
3. Terminology
observation angle. See Test Method E2540 for measurements
3.1 The terminology used in this test method generally
at a 0.5 degree observation angle.
agrees with that used in Terminology E284.
1.4 This standard does not purport to address all of the
3.2 Definitions—The delimiting phrase “in retroreflection”
safety concerns, if any, associated with its use. It is the
applies to each of the following definitions when used outside
responsibility of the user of this standard to establish appro-
the context of this or other retroreflection standards.
priate safety, health, and environmental practices and deter-
3.2.1 annular geometry, n—the portable instrument retrore-
mine the applicability of regulatory limitations prior to use.
flection collection method where an annular area 0.1 degrees
1.5 This international standard was developed in accor-
wide around the illumination axis collects the retroreflected
dance with internationally recognized principles on standard-
energyatanangletothecenteroftheannularareacorrespond-
ization established in the Decision on Principles for the
ing to a specific observation angle.
Development of International Standards, Guides and Recom-
3.2.2 coeffıcient of retroreflection, R ,n—of a plane retrore-
A
mendations issued by the World Trade Organization Technical
flecting surface, the ratio of the coefficient of luminous
Barriers to Trade (TBT) Committee.
intensity (R) of a plane retroreflecting surface to its area (A),
I
−1 −2
expressedincandelasperluxpersquaremetre(cd·lx ·m ).
This test method is under the jurisdiction of ASTM Committee E12 on Color
and Appearance and is the direct responsibility of Subcommittee E12.10 on
Retroreflection. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Feb. 1, 2022. Published February 2022. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ɛ2
approved in 1995. Last previous edition approved in 2016 as E1709–16 . DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E1709-16R22. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1709−16 (2022)
3.2.3 datum axis, n—adesignatedhalf-linefromtheretrore- 4.6 The reading displayed by the retroreflectometer is re-
flector center perpendicular to the retroreflector axis. corded. The retroreflectometer is then moved to another
position on the sign, and this value is recorded.Aminimum of
3.2.4 entrance angle, β,n—the angle between the illumina-
four readings shall be taken and averaged for each retroreflec-
tion axis and the retroreflector axis.
tive color or material on the sign to be tested.
3.2.5 entrance half-plane, n—the half plane that originates
on the line of the illumination axis and contains the retrore-
5. Significance and Use
flector axis.
5.1 Measurements made by this test method are related to
3.2.6 instrument standard, n—working standard used to
thenighttimebrightnessofretroreflectivetrafficsignsapproxi-
calibrate the portable retroreflectometer.
mately facing the driver of a mid-sized automobile equipped
with tungsten filament headlights at about 200 m distance.
3.2.7 observation angle, α,n—the angle between the illu-
mination axis and the observation axis.
5.2 Retroreflective material used on traffic signs degrades
withtimeandrequiresperiodicmeasurementtoensurethatthe
3.2.8 observation half-plane, n—the half plane that origi-
performanceoftheretroflectionprovidesadequatesafetytothe
nates on the line of the illumination axis and contains the
driver.
observation axis.
5.3 Thequalityofthesignastomaterialused,age,andwear
3.2.9 orientation angle, ω,n—the angle in a plane perpen-
s
pattern will have an effect on the coefficient of retroreflection.
diculartotheretroreflectoraxisfromtheentrancehalf-planeto
These conditions need to be observed and noted by the user.
the datum axis, measured counter-clockwise from the view-
point of the source.
5.4 This test method is not intended for use for the mea-
surement of signs when the instrument entrance and observa-
3.2.10 portable retroreflectometer, n—a hand-held instru-
tion angles differ from those specified herein.
ment that can be used in the field or in the laboratory for
measurement of retroreflectance.
6. Apparatus
3.2.10.1 Discussion—In this test method, “portable retrore-
NOTE 1—Paragraphs 6.1 and 6.2 are primarily addressing field
flectometer”referstoahand-heldinstrumentthatcanbeplaced
considerations, while paragraphs 6.3 through 6.5 address typical lab
in contact with sign material to measure the retroreflection in a
setting considerations.
standard geometry.
6.1 Portable Retroreflectometer—The retroreflectometer
3.2.11 presentation angle, γ,n—the dihedral angle from the
shallbeportable,withthecapabilityofbeingplacedatvarious
entrance half-plane to the observation half-plane, measured
locations on the signs. The retroreflectometer shall be con-
counter-clockwise from the viewpoint of the source.
structed so that placement on the sign will preclude stray light
(daylight) from entering the measurement area of the instru-
3.2.12 retroreflection, n—a reflection in which the reflected
ment and affecting the reading.
rays are returned preferentially in directions close to the
opposite of the direction of the incident rays, this property
6.2 Instrument Standard, or standards of desired color(s)
being maintained over wide variations of the direction of the
and material(s).
incident rays.
6.3 Light Source Requirements:
3.2.13 rotation angle,ε,n—theangleinaplaneperpendicu-
6.3.1 The projection optics shall be such that the illumi-
lar to the retroreflector axis from the observation half-plane to
nance at any point over the measurement area shall be within
the datum axis, measured counter-clockwise from the view-
10% of the average illuminance.
point of the source.
6.3.2 The aperture angle of the source as determined from
the center of the measurement area shall be not greater than
3.3 Definitions of entrance angle components β and β,as
1 2
0.1°.
well as other geometrical terms undefined in this test method,
may be found in Practice E808.
6.4 Receiver Requirements:
6.4.1 Thereceivershallhavesufficientsensitivityandrange
4. Summary of Test Method
to accommodate coefficient of retroreflection values from 0.1
−1 −2
to 1999.9 cd·lx ·m .
4.1 This test method involves the use of commercial por-
6.4.2 The combined spectral distribution of the light source
tableretroreflectometersfordeterminingtheretroreflectivityof
and the spectral responsivity of the receiver shall match the
highway signing materials.
combined spectral distribution of CIE Illuminant A and the
4.2 The entrance angle shall be –4°.
V(λ) spectral luminous efficiency function according to the
following criterion: For any choice of plano-parallel colored
4.3 The observation angle shall be 0.2°.
absorptive filter mounted in front of a white retroreflective
4.4 The portable retroreflectometer uses an instrument stan-
sample, the ratio of the R measured with the filter to the R
A A
dard for calibration.
measured without the filter shall be within 10% of the
4.5 After calibration, the retroreflectometer is placed in IlluminantAluminoustransmittanceofanairspacepairoftwo
contactwiththesigntobetested,ensuringthatonlythedesired such filters.
portion of the sign is within the measurement area of the 6.4.3 The instrument may be either a “point instrument” or
instrument. an “annular instrument,” depending on the shape of the
E1709−16 (2022)
receiver aperture (see Fig. 1). Point and annular instruments
make geometrically different measurements of R , which may
A
produce values differing on the order of 10%. Both measure-
mentsarevalidformostpurposes,buttheusershouldlearnthe
typeofinstrumentfromitsspecificationssheetandbeawareof
certain differences in operation and interpretation. For both
instrument types, the “up” position of the instrument shall be
known. Both types of instruments may make additional mea-
surements at observation angles other than the 0.5 degree of
thisspecificationandcombinethemeasurementattwoormore
different observation angles if the readings at the different
observation angles are reported separately.
6.4.3.1 The point instrument makes an R measurement
A
virtually identical to an R measurement made on a range
A
instrument following the procedure of Test Method E810. The
NOTE 1—For each instrument type, the illumination beam is 4°
downward. For the point instrument, receiver is above source.
–4° entrance angle would be set on a range instrument by
FIG. 2 Upright Optical Schematics
settingβ =–4°;β =0°.Thismaybecalled“-4°entranceangle.”
1 2
Therotationangle(ε)forthepointinstrumentisdeterminedby
the angular position of the instrument on the sign face.
Assuming the retroreflector’s datum axis to be upward, the 6.4.3.5 For both instrument types, the orientation angle (ω )
s
rotation angle equals 0° when the instrument is upright. is determined by the angular position of the instrument on the
Clockwiserotationoftheinstrumentonthesignfaceincreases sign face. It is the rotation angle (ε) rather than the orientation
the rotation angle. angle (ω ) which primarily affects retroreflection of signs
s
6.4.3.2 For the point instrument the “up” marking shall be measured at the small 4° entrance angle.
opposite the entrance half-plane. It shall be in the observation 6.4.3.6 Rotationally insensitive sheetings, such as glass
half-plane (see Fig. 2). bead sheetings, have R values that are nearly independent of
A
6.4.3.3 The annular instrument makes an R measurement the rotation angle. Accordingly, the point and annular instru-
A
similartoanaverageofalargenumberof R measurementson ments will make practically identical measurements of R for
A A
arangeinstrumentwithpresentationangle(γ)varyingbetween signs made with such sheetings.
–180° and +180°. For the 4° entrance angle the range instru- 6.4.3.7 Most prismatic retroreflectors are rotationally
ment would include the β and β settings indicated in Table 1. sensitive,having R valuesthatvarysignificantlywithrotation
1 2 A
There is no definite rotation angle (ε) for the annular instru- angle (ε), even at small entrance angles. The difference of R
A
ment. All values from –180° to +180° are included in the measurements made with the two types of instrument on
measurement. prismaticsignsmaybecomeasgreatas25%inextremecases,
6.4.3.4 Fortheannularinstrumentthe“up”markingshallbe
but is generally on the order of 10%. Neither the magnitude
opposite the entrance half-plane (see Fig. 2). nor the direction of difference can be predicted for unknown
FIG. 1 Annular and Point Aperture Instrument Angles
E1709−16 (2022)
TABLE 1 Laboratory Emulation of Annular Instrument Geometry
reasons for this collimation requirement. The first reason for
αβ β ε this collimation requirement is to avoid an observation angle
1 2
0.2° 3.86° –1.03° –165°
error in measurements or retroreflective signs consisting of
0.2° 3.47° –2.00° –150°
large optical elements as described in 8.1.4.2. The second
0.2° 2.83° –2.83° –135°
0.2° 2.00° –3.46° –120° reasonforthecollimationrequirementistomaintainaconstant
0.2° 1.04° –3.86° –105°
entrance angle over the sample area.
0.2° 0.00° –4.00° –90°
6.5.3 The entrance angle of the light source shall be−4° 6
0.2° –1.04° –3.86° –75°
0.2° –2.00° –3.46° –60°
1°.
0.2° –2.83° –2.83° –45°
0.2° –3.47° –2.00° –30°
7. Standardization
0.2° –3.86° –1.03° –15°
0.2° –4.00° 0.00° 0°
7.1 The retroreflectometer shall be calibrated or standard-
0.2° –3.86° 1.03° 15°
izedusinganinstrumentstandardconsistingofaseparatepanel
0.2° –3.47° 2.00° 30°
0.2° –2.83° 2.83° 45°
or disc of a material with a known R value. The calibration
A
0.2° –2.00° 3.46° 60°
values shall be maintained by checking against other standards
0.2° –1.04° 3.86° 75°
or by laboratory recalibration sufficiently often to ensure that
0.2° 0.00° 4.00° 90°
0.2° 1.04° 3.86° 105°
no large uncertainties in the measurement can occur.
0.2° 2.00° 3.46° 120°
7.1.1 Instrument standards are generally of glass-bead
0.2° 2.83° 2.83° 135°
0.2° 3.47° 2.00° 150° sheeting construction. The glass-bead sheeting instrument
0.2° 3.86° 1.03° 165°
standard shall be calibrated in the laboratory range instrument
0.2° 4.00° 0.00° 180°
at α=0.2°; β =–4°; β =0°; ε=0°. The glass-bead sheeting
1 2
standardmusthaveadatummarkforthecalibrationlaboratory,
but this mark is not required for its use with either type of
instrument.
samples.Thus, critical comparison of prismatic sign R values
A
7.1.2 If prismatic materials will be used as standards, they
measuredbyinstrumentsofthetwotypesisnotrecommended.
shall be calibrated differently for the two types of instrument.
6.4.3.8 Apointinstrumentcangagethevariationof R with
A
7.1.2.1 Aprismatic standard for a point instrument shall be
rotation angle by placing it with different angular positions
calibrated following the procedure of Test Method E810.It
upon the sign face. R variation of 5% for 5° rotation is not
A
shall be calibrated in the laboratory range instrument at α
unusual.Accordingly, repeatable R measurement of prismatic
A
=0.2°; β =–4°; β =0°; ε=0°.
signs with a point instrument, requires care in angular posi-
1 2
(a) The prismatic instrument standard must have a datum
tioning.
mark for the calibration laboratory, and this mark is required
6.4.3.9 An annular instrument cannot gage the variation of
for its use with the point instrument. The datum mark shall
R with rotation angle. Accordingly, repeatable R measure-
A A
align with the
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