ASTM C1549-02

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Designation: C 1549 – 02
Standard Test Method for
Determination of Solar Reflectance Near Ambient
Temperature Using a Portable Solar Reflectometer
This standard is issued under the fixed designation C 1549; 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.
1. Scope Horizontal and Low-Sloped Opaque Surfaces
2.2 Additional Reference:
1.1 This test method covers a technique for determining the
“Instructions for the Solar Spectrum Reflectometer Model
solar reflectance of flat opaque materials in a laboratory or in
SSR-ER,” Devices and Services Company
the field using a commercial portable solar reflectometer. The
purpose of the test method is to provide solar reflectance data
3. Terminology
required to evaluate temperatures and heat flows across sur-
3.1 Definitions—For definitions of some terms used in the
faces exposed to solar radiation.
test method, refer to Terminology C 168.
1.2 This test method does not supplant Test Method E 903
3.2 Definitions of Terms Specific to This Standard:
which measures solar reflectance over the wavelength range
3.2.1 air mass—air mass is related to the path length of
250 to 2500 nm using integrating spheres. The portable solar
solar radiation through the Earth’s atmosphere to the site of
reflectometer is calibrated using specimens of known solar
interest. Air mass 1 is for a path of normal solar radiation at the
reflectance to determine solar reflectance from measurements
Earth’s equator while air mass 2 indicates two times this path
at four wavelengths in the solar spectrum: 380 nm, 500 nm,
length.
650 nm, and 1220 nm. This technique is supported by
3.2.2 solar reflectance—the fraction of incident solar radia-
comparison of reflectometer measurements with measurements
tion upon a surface that is reflected from the surface.
obtained using Test Method E 903. This test method is appli-
3.3 Symbols:
cable to specimens of materials having both specular and
A = area normal to incident radiation, m
diffuse optical properties. It is particularly suited to the
Q = rate at which radiant heat is absorbed per m of
abs
measurement of the solar reflectance of opaque materials.
area, W
1.3 The values stated in SI units are to be regarded as the
q = solar flux, W/m
solar
standard. The values in parenthesis are for information only.
r = solar reflectance, dimensionless
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
4. Summary of Test Method
responsibility of the user of this standard to establish appro-
4.1 This test method employs a diffuse tungsten halogen
priate safety and health practices and determine the applica-
lamp to illuminate a flat specimen for two seconds out of a
bility of regulatory limitations prior to use.
ten-second measurement cycle. Reflected light is measured at
2. Referenced Documents an angle of 20° from the incident angle with four detectors.
Each detector is equipped with color filters to tailor its
2.1 ASTM Standards:
2 electrical response to a range of wavelengths in the solar
C 168 Terminology Relating to Thermal Insulation
spectrum. Software in the instrument combines the outputs of
E 691 Practice for Conducting an Interlaboratory Study to
3 the four detectors in appropriate proportions to approximate the
Determine the Precision of a Test Method
response for incident solar radiation through air mass 0, 1, 1.5,
E 903 Test Method for Solar Absorptance, Reflectance, and
or 2. The solar reflectance for the desired air mass is selectable
Transmittance of Materials Using Integrating Spheres
from the instrument’s keypad. The reflectances measured by
E 1980 Practice for Calculating Solar Reflectance Index of
the individual detectors are also available from the keypad and
digital readout. The instrument is calibrated using a black body
This test method is under the jurisdiction of ASTM Committee C16 on Thermal
Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal Annual Book of ASTM Standards, Vol 04.12.
Measurements. The sole source of supply of the apparatus known to the committee at this time
Current edition approved Oct. 10, 2002. Published October 2002. is Devices & Services Company, 10024 Monroe Drive, Dallas, TX 75229. If you are
Annual Book of ASTM Standards, Vol 04.06. aware of alternative suppliers, please provide this information to ASTM Interna-
Annual Book of ASTM Standards, Vol 14.02. tional Headquarters. Your comments will receive careful consideration at a meeting
Annual Book of ASTM Standards, Vol 12.02. of the responsible technical committee , which you may attend.
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C1549–02
cavity for a reflectance of zero and one or more surfaces of 6.1.2 Connecting Cable—A connecting cable, connects the
known solar reflectance provided by the manufacturer. A measurement head to the readout module. The connecting
surface to be evaluated is placed firmly against the 2.5 cm (1.0 cable transmits electrical signals from the four detectors to the
in.) diameter opening on the measurement head and maintained readout module.
in this position until constant readings are displayed by the 6.1.3 Readout Module—The readout module that is con-
digital readout. A comparison of techniques for measuring nected to the measurement head includes a keypad for control-
solar reflectance is available. ling the functions of the software, software for interpreting the
signals from the measurement head, and a digital readout for
5. Significance and Use
solar reflectivity or the display of input parameters or calibra-
5.1 The temperatures of opaque surfaces exposed to solar tion information. The resolution of the digital readout is 0.001.
radiation are generally higher than the adjacent air tempera- Detailed instructions for use of the keypad to communicate
tures. In the case of roofs or walls enclosing conditioned with the software are provided by the manufacturer of the
spaces, increased inward heat flows result. In the case of apparatus.
equipment or storage containers exposed to the sun, increased 6.1.4 Reference Standards—The calibration of the solar
operating temperatures usually result. The extent to which reflectometer is accomplished with a black body cavity that is
supplied by the manufacturer and at least one high-reflectance
solar radiation affects surface temperatures depends on the
solar reflectance of the exposed surface. A solar reflectance of standard. The solar reflectance of the high-reflectance standard
or standards are programmed into the software to facilitate
1.0 (100 % reflected) would mean no effect on surface tem-
perature while a solar reflectance of 0 (none reflected, all calibration. The apparatus accommodates up to eight solar
absorbed) would result in the maximum effect. Coatings of reflectance standards.
specific solar reflectance are used to change the temperature of 6.1.5 Test Specimens—Specimens to be tested for solar
surfaces exposed to sunlight. Coatings and surface finishes are reflectance shall be relatively flat and shall have a minimum
commonly specified in terms of solar reflectance. The initial dimension greater than 2.5 cm (1.0 in.) in order for the
(clean) solar reflectance must be maintained during the life of specimen to completely cover the measurement head opening.
the coating or finish to have the expected thermal performance. Test specimens of sufficient size are placed on top of the
5.2 The test method provides a means for periodic testing of measurement head. Position the measurement head against a
surfaces in the field or in the laboratory. Monitor changes in surface for in-situ or large area solar reflectance measurements.
solar reflectance due to aging and exposure, or both, with this
7. Procedure
test method.
7.1 Set-up—The instrument requires 110 volt AC power.
5.3 This test method is used to measure the solar reflectance
Take into account necessary safety precautions when using the
of a flat opaque surface. The precision of the average of several
instrument outside of conditioned spaces. Before power is
measurements is usually governed by the variability of reflec-
applied and the instrument is turned on, either end of the cable
tances on the surface being tested.
must be connected to the socket on the measurement head. The
5.4 Use the solar reflectance that is determined by this
other end must be connected to the socket on th
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