ASTM E1175-87(1996)

Designation: E 1175 – 87 (Reapproved 1996) An American National Standard
AMERICAN SOCIETY FOR TESTING AND MATERIALS
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Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
Determining Solar or Photopic Reflectance, Transmittance,
and Absorptance of Materials Using a Large Diameter
Integrating Sphere
This standard is issued under the fixed designation E 1175; 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 E 772 Terminology Relating to Solar Energy Conversion
E 892 Tables for Terrestrial Solar Spectral Irradiance at Air
1.1 This test method covers the measurement of the absolute
Mass 1.5 for a 37° Tilted Surface
total solar or photopic reflectance, transmittance, or absorp-
E 903 Test Method for Solar Absorptance, Reflectance, and
tance of materials and surfaces. Although there are several
Transmittance of Materials Using Integrating Spheres
applicable test methods employed for determining the optical
properties of materials, they are generally useful only for flat,
3. Terminology
homogeneous, isotropic specimens. Materials that are pat-
3.1 Definitions:
terned, textured, corrugated, or are of unusual size cannot be
3.1.1 absorptance, n—see Terminology E 772.
measured accurately using conventional spectrophotometric
3.1.2 integrating sphere—optical device used to either col-
techniques, or require numerous measurements to obtain a
lect flux reflected or transmitted from a sample into a hemi-
relevant optical value. The purpose of this test method is to
sphere or to provide isotropic irradiation of a sample from a
provide a means for making accurate optical property measure-
complete hemisphere.
ments of spatially nonuniform materials.
3.1.2.1 Discussion—It consists of a cavity that is approxi-
1.2 This test method is applicable to large specimens of
mately spherical in shape with apertures for admitting and
materials having both specular and diffuse optical properties. It
detecting flux and usually having additional apertures over
is particularly suited to the measurement of the reflectance of
which sample and reference specimens are placed.
opaque materials and the reflectance and transmittance of
3.1.3 photopic optical properties, n—absorptance, reflec-
semitransparent materials including corrugated fiber-reinforced
tance, and transmittance of a sample evaluated as the weighted
plastic, composite transparent and translucent samples, heavily
average of the measured property, with the wavelength by
textured surfaces, and nonhomogeneous materials such as
wavelength of the product of the spectral irradiance for the
woven wood, window blinds, draperies, etc.
measurement and the Commission Internationale de
1.3 The values stated in SI units are to be regarded as the
l’Eclairage (CIE) photopic spectral response, as the weighting
standard. The values given in parentheses are for information
function.
only.
3.1.4 photopic response, n—spectral response of the aver-
1.4 This standard does not purport to address all of the
age human eye when fully adapted to daylight conditions.
safety concerns, if any, associated with its use. It is the
3.1.5 reflectance, n—see Terminology E 772.
responsibility of the user of this standard to establish appro-
3.1.6 transmittance, n—see Terminology E 772.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. (For specific safety
4. Summary of Test Method
hazards, see Note 1.)
4.1 This test method describes a procedure and apparatus
2. Referenced Documents for determining the area-averaged optical properties of com-
plex or nonuniform materials and surfaces. This test method
2.1 ASTM Standards:
employs a large diameter integrating sphere and a source
1 2
This test method is under the jurisdiction of ASTM Committee E-44 on Solar, Annual Book of ASTM Standards, Vol 12.02.
Geothermal, and Other Alternative Energy Sources and is the direct responsibility of Annual Book of ASTM Standards, Vol 14.02.
Subcommittee E44.04 on Materials Performance. Commission Internationale de l’Eclairage (CIE), International Light Vocabu-
Current edition approved July 31, 1987. Published September 1987. lary, 3rd Ed., Bureau Central de la CIE, Paris, 1970.
E 1175
capable of illuminating a representative area of the test 6.2 The sphere shall be mounted in such a manner as to
specimen’s surface. permit precision illumination of the sample at directions of
4.2 Transmittance is determined with the specimen mounted incidence from 0° (normal incidence) to 60° from normal in the
5,6
externally at the sphere entrance port. Reflectance is deter- transmittance mode, using natural sunlight as source. When
mined by placing the specimen in the center of the integrating employing an artificial source for either simulated solar or
sphere, in accordance with the diagram in Fig. A1.2 of Test photopic measurements, the off-angle mechanism may either
Method E 903. For measurement of reflectance of partially be made a part of the sphere (with a fixed position lamp) or a
transmitting samples, the sample should be backed by a black part of the source assembly (with a fixed position sphere).
opaque absorber to eliminate the transmitted flux from the 6.3 For reflectance measurements, a center-positioned
measurement. sample mount that has two degrees of freedom is required: in
4.3 The source may be either natural sunlight or an artificial and out of the sample beam, and rotation about the sample
source that closely approximates an Air Mass 1.5 solar energy beam to provide incident angles from 0° to 660°. The sample
distribution in accordance with Tables E 892. mount shall be designed so that the flux transmitted by the
4.4 Relevant optical properties are determined by the ratio sample is absorbed, for measurement of reflectance, or so that
of the total sphere flux transmitted or reflected by the specimen the sample is supported by its rim for simultaneous measure-
to the total sphere flux, or both when no specimen is in place. ment of reflectance plus transmittance.
4.5 The use of a spectrally flat or spectrally sensitive 6.4 The interior of the integrating sphere shall be uniformly
detector determines whether a solar or a photopic optical coated with a spectrally flat paint having a minimum hemi-
characteristic is measured. spherical reflectance of 0.85 in the spectral region of interest.
For photopic measurements only, nearly any flat interior white
5. Significance and Use
paint will suffice. For solar and ultraviolet measurements, a
good barium sulfate-pigmented sphere paint is required.
5.1 To overcome the inadequacies of conventional spectro-
photometric measurement techniques when nonhomogeneous 6.5 A stable source illuminant having a spectral distribution
approximating that of a standard solar spectrum of Air Mass
materials are measured, a large integrating sphere may be
5,6
used. Since the beam employed in such spheres is large in 1.5 (Tables E 892) shall be employed for simulated solar
measurements. Other sources may be employed for photopic
comparison to the disparaties of the materials being tested, the
nonisotropic nature of the specimen being measured is essen- measurements if the spectral energy distribution is essentially
tially averaged, or integrated out of the measurement, in a flat in the 475 to 650-nm region.
single experimental determination. 6.6 For natural sunshine illumination, a solar siderostat (or
5.2 Solar and photopic optical properties may be measured heliostat) arrangement is required to provide uniform illumi-
either with monofunctional spheres individually tailored for the nation (unless the sphere is itself operated in an altazimuthal
measurement of either transmittance or reflectance, or may be tracking mode). Data should be taken during the time of day
measured with a single multifunctional sphere that is employed that ensures a normal incident global (hemispherical) irradi-
to measure both transmi
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