ASTM E972-96(2007)
(Test Method)Standard Test Method for Solar Photometric Transmittance of Sheet Materials Using Sunlight
Standard Test Method for Solar Photometric Transmittance of Sheet Materials Using Sunlight
SIGNIFICANCE AND USE
Glazed apertures in buildings are generally utilized for the controlled admission of both light and solar radiant heat energy into the structure. Other devices may also be used to reflect light and solar radiant heat into a building.
The bulk of the solar radiant energy entering a building in this manner possesses wavelengths that lie from 300 to 2500 nm (3000 to 25 000 E). Only the portion from 380 to 760 nm (3800 to 7600 E) is visible radiation, however. In daylighting applications, it is therefore important to distinguish the radiant (solar radiant energy) transmittance or reflectance of these materials from their luminous (light) transmittance or reflectance.
For comparisons of the energy and illumination performances of building fenestration systems it is important that the calculation or measurement, or both, of solar radiant and luminous transmittance and reflectance of materials used in fenestration systems use the same incident solar spectral distribution.
Solar luminous transmittance and reflectance are important properties in describing the performance of components of solar illumination systems including windows, clerestories, skylights, shading and reflecting devices, and other passive fenestrations that permit the passage of daylight as well as solar radiant heat energy into buildings.
This test method is useful for determining the solar luminous transmittance and reflectance of optically inhomogeneous sheet materials and diffusely reflecting materials used in natural lighting systems that are used alone or in conjunction with passive or active solar heating systems, or both. This test method provides a means of measuring solar luminous transmittance under fixed conditions of incidence and viewing. This test method has been found practical for both transparent and translucent materials as well as for those with transmittances reduced by reflective coatings. This test method is particularly applicable to the measurement of luminous transmittance...
SCOPE
1.1 This test method covers the measurement of solar photometric transmittance of materials in sheet form. Solar photometric transmittance is measured using a photometer (illuminance meter) in an enclosure with the sun and sky as the source of radiation. The enclosure and method of test is specified in Test Method E 1175 (or Test Method E 1084).
1.2 The purpose of this test method is to specify a photometric sensor to be used with the procedure for measuring the solar photometric transmittance of sheet materials containing inhomogeneities in their optical properties.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E972 − 96(Reapproved 2007)
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 3. Terminology
3.1 Definitions—For definitions of other terms used in this
1.1 This test method covers the measurement of solar
test method, refer to Terminology E772.
photometric transmittance of materials in sheet form. Solar
3.1.1 illuminance, n—luminous irradiance.
photometric transmittance is measured using a photometer
(illuminance meter) in an enclosure with the sun and sky as the
3.1.2 luminous (photometric), adj—referring to a radiant
source of radiation. The enclosure and method of test is
(or radiometric) quantity,indicatestheweightedaverageofthe
specified in Test Method E1175 (or Test Method E1084).
spectral radiometric quantity, with the photopic spectral lumi-
nous efficiency function (see Annex A1) being the weighting
1.2 The purpose of this test method is to specify a photo-
function.
metric sensor to be used with the procedure for measuring the
3.1.3 radiant flux, Φ = d Q/dt[Watt (W)], n— power
solar photometric transmittance of sheet materials containing
emitted, transferred, or received in the form of electromagnetic
inhomogeneities in their optical properties.
waves or photons. See radiometric properties and quantities.
1.3 This standard does not purport to address all of the
3.1.4 reflectance, ρ, Φ /Φ,n—the ratio of the reflected flux
r i
safety concerns, if any, associated with its use. It is the
to the incident flux.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- 3.1.5 solar irradiance at a point of a surface, E =dΦ/dA,
s
n—the quotient of the solar flux incident on an element of a
bility of regulatory limitations prior to use.
surface containing the point, by the area of that element,
measured in watts per square metre.
2. Referenced Documents
3.1.5.1 Discussion—Measured values of transmittance and
2.1 ASTM Standards:
reflectance depend upon angle of incidence, solid angles of
E772 Terminology of Solar Energy Conversion
incidence and of transmission and reflection, the method of
E1084 Test Method for Solar Transmittance (Terrestrial) of
measurement of the reflected or transmitted flux, and the
Sheet Materials Using Sunlight
spectral composition of the incident flux. Because of this
E1175 Test Method for Determining Solar or Photopic
dependence, complete information on the technique and con-
Reflectance, Transmittance, andAbsorptance of Materials
ditions of measurement should be specified.
Using a Large Diameter Integrating Sphere
3.1.6 solar, adj—(1) referring to a radiometric term, indi-
2.2 CIE Standard:
cates that the quantity has the sun as a source or is character-
Standard Illuminant D65
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
These test methods are under the jurisdiction of ASTM Committee E44 on
3.1.7 spectral, adj—(1) for dimensionless optical
Solar, Geothermal and Other Alternative Energy Sources and is the direct respon-
properties, indicates that the property was evaluated at a
sibility of Subcommittee E44.05 on Solar Heating and Cooling Systems and
specific wavelength, λ, within a small wavelength interval, ∆λ
Materials.
Current edition approved March 1, 2007. Published July 2007. Originally
aboutλ,symbolwavelengthinparentheses,as L(350nm,3500
approved in 1983. Last previous edition approved in 2002 as E972 – 96 (2002).
Å), or as a function of wavelength, symbol L(λ). (2) for a
DOI: 10.1520/E0972-96R07.
radiometric quantity, indicates the concentration of the quan-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
tity per unit wavelength or frequency, indicated by the sub-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
dL
Standards volume information, refer to the standard’s Document Summary page on
script lambda, as L = ⁄dλ, at a specific wavelength. The
λ
the ASTM website.
wavelength at which the spectral concentration is evaluated
Available from Commission Internationale de l’Eclairage (International Com-
may be indicated by the wavelength in parentheses following
mission on Illumination), Barean Central de la CIE, 4 Av. du Recteur Poincaré,
75-Paris, France. the symbol, L (350 nm).
λ
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959. United States
E972 − 96 (2007)
3.1.8 transmittance,τ =Φ /Φ,n—the ratio of the transmit- exception that the sensing element shall be replaced by the
t i
ted flux to the incident radiant flux. sensing element described by this test method.
6.1.1 The sensing element of this instrument shall be a
4. Summary of Test Method
photometer (illuminance meter) consisting of a suitable radia-
4.1 Using sunlight as the source and a photometer as the
tion detector (such as a silicon photovoltaic device), a filter,
detector, the specimen is made to be the cover of an enclosure
and a diffusing element. The filter shall be designed so that the
with the plane of the specimen normal to the direct component
spectral response of the photometer very closely matches that
of the incident solar radiation. Luminous transmittance is
of the standard human observer, as specified by the C.I.E.
measured as the ratio of the transmitted illuminance to the
photopic spectral luminous efficiency function tabulated in
incident illuminance.
Annex A1. The response of the photometer at wavelength λ,
divided by its response at 555 nm (5550 Å), shall depart from
5. Significance and Use
the spectral luminous efficiency of the standard human ob-
5.1 Glazed apertures in buildings are generally utilized for
server at wavelength λ by no more than 2 % for all wave-
the controlled admission of both light and solar radiant heat
lengths from 390 to 750 nm (3900 to 7500 Å). Photometer
energy into the structure. Other devices may also be used to
response shall be essentially zero outside this range.
reflect light and solar radiant heat into a building. 4
6.1.2 Cosine Response —The response of the photometer to
5.2 The bulk of the solar radiant energy entering a building
uniform, collimated incident radiation at an angle θ of
in this manner possesses wavelengths that lie from 300 to 2500 incidence, divided by its response at normal incidence (θ = 0°),
nm (3000 to 25 000 Å). Only the portion from 380 to 760 nm
shall depart from the cosine of θ by no more than (θ ÷ 18) %,
(3800 to 7600 Å) is visible radiation, however. In daylighting with θ in deg.
applications, it is therefore important to distinguish the radiant
6.1.3 Thediffusingelementanddetectorelectronicsshallbe
(solar radiant energy) transmittance or reflectance of these designed so that the voltage (or current) output of the sensor is
materials from their luminous (light) transmittance or reflec-
proportionaltohemisphericalilluminanceincidentuponit.The
tance.
photometer shall be located inside the box so that its entrance
aperture (the diffusing element) is centered approximately 50
5.3 For comparisons of the energy and illumination perfor-
mm (2 in.) below the plane of the rim of the box. Other
mances of building fenestration systems it is important that the
instructions shall be closely followed.
calculation or measurement, or both, of solar radiant and
luminous transmittance and reflectance of materials used in
7. Test Specimens
fenestration systems use the same incident solar spectral
distribution.
7.1 The test specimens shall be as described in Test Method
E1175 (or Test
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