ASTM E972-96(2021)

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: E972 − 96 (Reapproved 2021)
Standard Test Method for
Solar Photometric Transmittance of Sheet Materials Using
Sunlight
This standard is issued under the fixed designation E972; 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 2.2 CIE Standard:
Standard Illuminant D65
1.1 This test method covers the measurement of solar
photometric transmittance of materials in sheet form. Solar
3. Terminology
photometric transmittance is measured using a photometer
3.1 Definitions—For definitions of other terms used in this
(illuminance meter) in an enclosure with the sun and sky as the
test method, refer to Terminology E772.
source of radiation. The enclosure and method of test is
3.1.1 illuminance, n—luminous irradiance.
specified in Test Method E1175 (or Test Method E1084).
3.1.2 luminous (photometric), adj—referring to a radiant
1.2 The purpose of this test method is to specify a photo-
(or radiometric) quantity,indicatestheweightedaverageofthe
metric sensor to be used with the procedure for measuring the
spectral radiometric quantity, with the photopic spectral lumi-
solar photometric transmittance of sheet materials containing
nous efficiency function (see Annex A1) being the weighting
inhomogeneities in their optical properties.
function.
1.3 This standard does not purport to address all of the
3.1.3 radiant flux, Φ = d Q/dt[Watt (W)], n— power
safety concerns, if any, associated with its use. It is the
emitted, transferred, or received in the form of electromagnetic
responsibility of the user of this standard to establish appro-
waves or photons. See radiometric properties and quantities.
priate safety, health, and environmental practices and deter-
3.1.4 reflectance, ρ, Φ /Φ,n—the ratio of the reflected flux
mine the applicability of regulatory limitations prior to use.
r i
to the incident flux.
1.4 This international standard was developed in accor-
dance with internationally recognized principles on standard-
3.1.5 solar irradiance at a point of a surface, E =dΦ⁄dA,
s
ization established in the Decision on Principles for the
n—the quotient of the solar flux incident on an element of a
Development of International Standards, Guides and Recom-
surface containing the point, by the area of that element,
mendations issued by the World Trade Organization Technical
measured in watts per square metre.
Barriers to Trade (TBT) Committee.
3.1.5.1 Discussion—Measured values of transmittance and
reflectance depend upon angle of incidence, solid angles of
2. Referenced Documents incidence and of transmission and reflection, the method of
measurement of the reflected or transmitted flux, and the
2.1 ASTM Standards:
spectral composition of the incident flux. Because of this
E772 Terminology of Solar Energy Conversion
dependence, complete information on the technique and con-
E1084 Test Method for Solar Transmittance (Terrestrial) of
ditions of measurement should be specified.
Sheet Materials Using Sunlight
3.1.6 solar, adj—(1) referring to a radiometric term, indi-
E1175 Test Method for Determining Solar or Photopic
cates that the quantity has the sun as a source or is character-
Reflectance, Transmittance, andAbsorptance of Materials
Using a Large Diameter Integrating Sphere istic of the sun. (2) referring to an optical property, indicates
the weighted average of the spectral optical property, with the
solar spectral irradiance E used as the weighting function.
sλ
1 3.1.7 spectral, adj—(1) for dimensionless optical
This test method is under the jurisdiction of ASTM Committee E44 on Solar,
Geothermal and OtherAlternative Energy Sources and is the direct responsibility of
properties, indicates that the property was evaluated at a
Subcommittee E44.20 on Optical Materials for Solar Applications.
specific wavelength, λ, within a small wavelength interval, ∆λ
Current edition approved Jan. 1, 2021. Published January 2021. Originally
aboutλ,symbolwavelengthinparentheses,as L(350nm,3500
approved in 1983. Last previous edition approved in 2013 as E972 – 96 (2013).
DOI: 10.1520/E0972-96R21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Available from Commission Internationale de l’Eclairage (International Com-
Standards volume information, refer to the standard’s Document Summary page on mission on Illumination), Barean Central de la CIE, 4 Av. du Recteur Poincaré,
the ASTM website. 75-Paris, France.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959. United States
E972 − 96 (2021)
Å), or as a function of wavelength, symbol L(λ). (2) for a 6. Apparatus
radiometric quantity, indicates the concentration of the quan-
6.1 The apparatus to be used in this test method shall be as
tity per unit wavelength or frequency, indicated by the sub-
described in either Test Method E1175 or E1084, with the
dL
script lambda, as L = ⁄dλ, at a specific wavelength. The
λ
exception that the sensing element shall be replaced by the
wavelength at which the spectral concentration is evaluated
sensing element described by this test method.
may be indicated by the wavelength in parentheses following
6.1.1 The sensing element of this instrument shall be a
the symbol, L (350 nm).
λ
photometer (illuminance meter) consisting of a suitable radia-
3.1.8 transmittance, τ =Φ /Φ,n—the ratio of the transmit-
t i
tion detector (such as a silicon photovoltaic device), a filter,
ted flux to the incident radiant flux.
and a diffusing element. The filter shall be designed so that the
spectral response of the photometer very closely matches that
4. Summary of Test Method
of the standard human observer, as specified by the C.I.E.
4.1 Using sunlight as the source and a photometer as the
photopic spectral luminous efficiency function tabulated in
detector, the specimen is made to be the cover of an enclosure
Annex A1. The response of the photometer at wavelength λ,
with the plane of the specimen normal to the direct component
divided by its response at 555 nm (5550 Å), shall depart from
of the incident solar radiation. Luminous transmittance is
the spectral luminous efficiency of the standard human ob-
measured as the ratio of the transmitted illuminance to the
serveratwavelengthλbynomorethan2 %forallwavelengths
incident illuminance.
from 390 to 750 nm (3900 to 7500 Å). Photometer response
5. Significance and Use shall be essentially zero outside this range.
6.1.2 Cosine Response —The response of the photometer to
5.1 Glazed apertures in buildings are generally utilized for
uniform, collimated incident radiation at an angle θ of
the controlled admission of both light and solar radiant heat
incidence, divided by its response at normal incidence (θ = 0°),
energy into the structure. Other devices may also be used to
shall depart from the cosine of θ by no more than (θ ÷ 18) %,
reflect light and solar radiant heat into a building.
with θ in deg.
5.2 The bulk of the solar radiant energy entering a building
6.1.3 Thediffusingelementanddetectorelectronicsshallbe
in this manner possesses wavelengths that lie from 300 to 2500
designed so that the voltage (or current) output of the sensor is
nm (3000 to 25 000 Å). Only the portion from 380 to 760 nm
proportionaltohemisphericalilluminanceincidentuponit.The
(3800 to 7600 Å) is visible radiation, however. In daylighting
photometer shall be located inside the box so that its entrance
applications, it is therefore important to distinguish the radiant
aperture (the diffusing element) is centered approximately 50
(solar radiant energy) transmittance or reflectance of these
mm (2 in.) below the plane of the rim of the box. Other
materials from their luminous (light) transmittance or reflec-
instructions shall be closely followed.
tance.
5.3 For comparisons of the energy and illumination perfor-
7. Test Specimens
ma
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