ASTM E972-96

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
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Designation: E 972 – 96 An American National Standard
Standard Test Method for
Solar Photometric Transmittance of Sheet Materials Using
Sunlight
This standard is issued under the fixed designation E 972; 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 3.1.2 luminous (photometric), adj—referring to a radiant
(or radiometric) quantity, indicates the weighted average of the
1.1 This test method covers the measurement of solar
spectral radiometric quantity, with the photopic spectral lumi-
photometric transmittance of materials in sheet form. Solar
nous efficiency function (see Annex A1) being the weighting
photometric transmittance is measured using a photometer
function.
(illuminance meter) in an enclosure with the sun and sky as the
3.1.3 radiant flux, F=d Q/dt[Watt (W)], n—power emit-
source of radiation. The enclosure and method of test is
ted, transferred, or received in the form of electromagnetic
specified in Test Method E 1175 (or Test Method E 1084).
waves or photons. See radiometric properties and quantities.
1.2 The purpose of this test method is to specify a photo-
3.1.4 reflectance, r, F /F , n—the ratio of the reflected flux
r i
metric sensor to be used with the procedure for measuring the
to the incident flux.
solar photometric transmittance of sheet materials containing
3.1.5 solar irradiance at a point of a surface, E =dF/dA,
s
inhomogeneities in their optical properties.
n—the quotient of the solar flux incident on an element of a
1.3 This standard does not purport to address all of the
surface containing the point, by the area of that element,
safety concerns, if any, associated with its use. It is the
measured in watts per square metre.
responsibility of the user of this standard to establish appro-
3.1.5.1 Discussion—Measured values of transmittance and
priate safety and health practices and determine the applica-
reflectance depend upon angle of incidence, solid angles of
bility of regulatory limitations prior to use.
incidence and of transmission and reflection, the method of
2. Referenced Documents
measurement of the reflected or transmitted flux, and the
spectral composition of the incident flux. Because of this
2.1 ASTM Standards:
dependence, complete information on the technique and con-
E 772 Terminology Relating to Solar Energy Conversion
ditions of measurement should be specified.
E 891 Tables for Terrestrial Direct Normal Solar Spectral
3.1.6 solar, adj—(1) referring to a radiometric term, indi-
Irradiance for Air Mass 1.5
cates that the quantity has the sun as a source or is character-
E 1084 Test Method for Solar Transmittance (Terrestrial) of
istic of the sun. (2) referring to an optical property, indicates
Sheet Materials Using Sunlight
the weighted average of the spectral optical property, with the
E 1175 Test Method for Determining Solar or Photopic
solar spectral irradiance E used as the weighting function.
Reflectance, Transmittance, and Absorptance of Materials sl
3.1.7 spectral, adj—(1) for dimensionless optical proper-
Using a Large Diameter Integrating Sphere
ties, indicates that the property was evaluated at a specific
2.2 CIE Standard:
wavelength, l, within a small wavelength interval, Dl about l,
Standard Illuminant D65
symbol wavelength in parentheses, as L (350 nm, 3500 Å), or
3. Terminology
as a function of wavelength, symbol L (l). (2) for a radiomet-
ric quantity, indicates the concentration of the quantity per unit
3.1 Definitions—For definitions of other terms used in this
wavelength or frequency, indicated by the subscript lambda, as
test method, refer to Terminology E 772.
dL
L = ⁄dl, at a specific wavelength. The wavelength at which
3.1.1 illuminance, n—luminous irradiance. l
the spectral concentration is evaluated may be indicated by the
wavelength in parentheses following the symbol, L (350 nm).
l
These test methods are under the jurisdiction of ASTM Committee E44 on 3.1.8 transmittance, t = F /F , n—the ratio of the transmit-
t i
Solar, Geothermal, and Other Alternative Energy Sources and is the direct
ted flux to the incident radiant flux.
responsibility of Subcommittee E44.05 on Solar Heating and Cooling Subsystems
and Systems.
4. Summary of Test Method
Current edition approved April 10, 1996. Published May 1996. Originally
published as E 972 – 83. Last previous edition E 972 – 88 (1992). 4.1 Using sunlight as the source and a photometer as the
Annual Book of ASTM Standards, Vol 12.02.
detector, the specimen is made to be the cover of an enclosure
Available from Commission Internationale de l’Eclairage (International Com-
with the plane of the specimen normal to the direct component
mission on Illumination), Barean Central de la CIE, 4 Av. du Recteur Poincaré,
of the incident solar radiation. Luminous transmittance is
75-Paris, France.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 972
measured as the ratio of the transmitted illuminance to the tion detector (such as a silicon photovoltaic device), a filter,
incident illuminance. and a diffusing element. The filter shall be designed so that the
spectral response of the photometer very closely matches that
5. Significance and Use
of the standard human observer, as specified by the C.I.E.
5.1 Glazed apertures in buildings are generally utilized for
photopic spectral luminous efficiency function tabulated in
the controlled admission of both light and solar radiant heat Annex A1. The response of the photometer at wavelength l,
energy into the structure. Other devices may also be used to
divided by its response at 555 nm (5550 Å), shall depart from
reflect light and solar radiant heat into a building. the spectral luminous efficiency of the standard human ob-
5.2 The bulk of the solar radiant energy entering a building
server at wavelength l by no more than 2 % for all wave-
in this manner possesses wavelengths that lie from 300 to 2500 lengths from 390 to 750 nm (3900 to 7500 Å). Photometer
nm (3000 to 25 000 Å). Only the portion from 380 to 760 nm
response shall be essentially zero outside this range.
(3800 to 7600 Å) is visible radiation, however. In daylighting 6.1.2 Cosine Response —The response of the photometer to
applications, it is therefore important to distinguish the radiant
uniform, collimated incident radiation at an angle u of inci-
(solar radiant energy) transmittance or reflectance of these dence, divided by its response at normal incidence (u = 0°),
materials from their luminous (light) transmittance or reflec-
shall depart from the cosine of u by no more than (u4 18) %,
tance. with u in deg.
5.3 For comparisons of the energy and illumination perfor-
6.1.3 The diffusing element and detector electronics shall be
mances of building fenestration systems it is important that the designed so that the voltage (or current) output of the sensor is
calculation or measurement, or both, of solar radiant and
proportional to hemispherical illuminance incident upon it. The
luminous transmittance and reflectance of materials used in
photometer shall be located inside the box so that its entrance
fenestration systems use the same incident solar spectral aperture (the diffusing element) is centered approximately 50
distribution.
mm (2 in.) below the plane of the rim of the box. Other
5.4 Solar luminous transmittance and reflectance are impor- instructions shall be closely followed.
tant properties in describing the performance of components of
7. Test Specimens
solar illumination systems including windows, clerestories,
skylights, shading and reflecting devices, and other passive
7.1 The test specimens shall be as described in Tes
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