ASTM E971-88(2003)
(Practice)Standard Practice for Calculation of Photometric Transmittance and Reflectance of Materials to Solar Radiation
Standard Practice for Calculation of Photometric Transmittance and Reflectance of Materials to Solar Radiation
SIGNIFICANCE AND USE
Glazed apertures in buildings are commonly 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.
5.1.1 Most of the solar radiant energy entering a building in this manner possesses wavelengths that lie between 300 and 2500 nm (3000 to 25 000 E). Only the portion between 380 and 760 nm is visible radiation, however. In daylighting applications, it is therefore important to distinguish the solar radiant energy transmittance and reflectance of these materials from their luminous (visual or photometric) transmittance and 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 irradiance distribution.
5.2.1 Solar luminous transmittance and reflectance are important properties in describing the performance of components of solar illumination systems (for example, windows, clerestories, skylights, shading and reflecting devices) and other fenestrations that permit the passage of daylight as well as solar energy into buildings.
This practice is useful for determining the luminous transmittance and reflectance of glazing materials and diffusely or quasi-diffusely reflecting materials used in daylighting systems. For the results of this practice to be meaningful, inhomogeneities or corrugations in the sample must not be large. Test Method E 1175 (or Test Method E 972) is available for sheet materials that do not satisfy this criterion.
SCOPE
1.1 This practice describes the calculation of luminous (photometric) transmittance and reflectance of materials from spectral radiant transmittance and reflectance data obtained from Test Method E 903.
1.2 Determination of luminous transmittance by this practice is preferred over measurement of photometric transmittance by methods using the sun as a source and a photometer as detector except for transmitting sheet materials that are inhomogeneous, patterned, or corrugated.
1.3 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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Standards Content (Sample)
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Designation: E971 – 88 (Reapproved 2003)
Standard Practice for
Calculation of Photometric Transmittance and Reflectance
of Materials to Solar Radiation
This standard is issued under the fixed designation E971; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Standard Illuminator D65
1.1 This practice describes the calculation of luminous
3. Terminology
(photometric) transmittance and reflectance of materials from
3.1 Definitions—For definitions of other terms used in this
spectral radiant transmittance and reflectance data obtained
practice, refer to Terminology E772.
from Test Method E903.
3.1.1 illuminance, n—luminous irradiance.
1.2 Determination of luminous transmittance by this prac-
3.1.2 luminous (photometric), adj—referring to a radiomet-
tice is preferred over measurement of photometric transmit-
ric quantity, indicates the weighted average of the spectral
tance by methods using the sun as a source and a photometer
radiometric quantity, with the photopic spectral luminous
as detector except for transmitting sheet materials that are
efficiency function given in Annex A1 being the weighting
inhomogeneous, patterned, or corrugated.
function (see Appendix X1).
1.3 This standard does not purport to address all of the
3.1.3 radiant flux, F = dQ/dt[Watt(W)], n—poweremitted,
safety concerns, if any, associated with its use. It is the
transferred, or received in the form of electromagnetic waves
responsibility of the user of this standard to establish appro-
or photons. See radiometric properties and quantities.
priate safety and health practices and determine the applica-
3.1.4 solar irradiance at a point of a surface, E =dF/dA,
s
bility of regulatory limitations prior to use.
n—the quotient of the solar flux incident on an element of a
2. Referenced Documents surface containing the point, by the area of that element,
measured in watts per square metre.
2.1 ASTM Standards:
3.1.5 solar, adj—(1) referring to a radiometric term, indi-
E772 Terminology Relating to Solar Energy Conversion
cates that the quantity has the sun as a source or is character-
E891 Tables for Terrestrial Direct Normal Solar Spectral
istic of the sun. (2) referring to an optical property, indicates
Irradiance for Air Mass 1.5
the weighted average of the spectral optical property, with the
E903 Test Method for Solar Absorptance, Reflectance, and
solar spectral irradiance E used as the weighting function.
sl
Transmittance of Materials Using Integrating Spheres
3.1.6 spectral, adj—(1) for dimensionless optical proper-
E972 Test Method for Solar Photometric Transmittance of
ties, indicates that the property was evaluated at a specific
Sheet Materials Using Sunlight
wavelength, l,withinasmallwavelengthinterval, Dlabout l.
E1175 Test Method for Determining Solar or Photopic
Symbol wavelength in parentheses, as L (350 nm, 3500Å), or
Reflectance, Transmittance, and Absorptance of Materials
as a function of wavelength, symbol L (l). (2) for a radiomet-
Using a Large Diameter Integrating Sphere
ric quantity,indicatestheconcentrationofthequantityperunit
2.2 CIE Standard:
wavelengthorfrequency,indicatedbythesubscriptlambda,as
L = dL/dl,ataspecificwavelength.Thewavelengthatwhich
l
the spectral concentration is evaluated may be indicated by the
These test methods are under the jurisdiction of ASTM Committee E44 on
wavelength in parentheses following the symbol, L (350 nm).
l
Solar, Geothermal, and Other Alternative Energy Sources and is the direct
responsibility of Subcommittee E44.05 on Solar Heating and Cooling Subsystems
4. Summary of Practice
and Systems.
Current edition approved Aug. 26, 1988. Published December 1988. Originally
4.1 Spectral transmittance or reflectance data between
e1
approved in 1983. Last previous edition approved in 1996 as E971–85(1996) .
wavelengths of 380 and 760 nm (3800 to 7600 Å), which have
DOI: 10.1520/E0971-88R03.
been obtained in accordance with Test Method E903, are
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 multiplied by solar spectral irradiance values provided in
Standards volume information, refer to the standard’s Document Summary page on
Standard Tables E891 and by the photopic spectral luminous
the ASTM website.
Withdrawn. The last approved version of this historical standard is referenced
on www.astm.org.
AvailablefromCommissionInternationaledel’Eclairage,BureauCentraldela
CIE, 4 Av. du Recteur Poincaré, 75-Paris, France.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959, United States.
E971 – 88 (2003)
efficiency function (see Annex A1). The resulting product is 6. Procedure
integrated over the spectral range from 380 to 760 nm using a
6.1 Measurements—Measure spectral transmittance data
summation procedure to approximate the integral. This sum-
t(l) or spectral reflectance data r(l) from 380 nm to 760 nm
i i
mation procedure is then repeated with the product of the solar
as described in Test Method E903.
energyspectraldistributionandthephotopicspectralluminous
6.2 Calculations—Calculate the photometric transmittance
efficiency. The ratio of the two integrals is the solar luminous
t or reflectance r using Eq 1 as follows:
v v
(photometric) transmittance or reflectance of the measured
N N
sample.
r or t 5 ~ [r~l !or t ~l !#·E V Dl/ E V (1)
v v ( i i li li i ( li li
i 51 i 51
5. Significance and Use
where:
E = terrestrial direct normal solar spectral irradiance for
li
5.1 Glazed apertures in buildings are commonly utilized for
air mass 1.5 provided in Tables E891,
the controlled admission of both light and solar radiant heat
V = photopic spectral luminous efficiency function given
l
energy into the structure. Other devices may also be used to
in Annex A1, and
reflect light and solar radiant heat into a building.
N = number of wavelengths for which E is known
l
5.1.1 Most of the solar radiant energy entering a building in
between 380 nm and 760 nm.
this manner possesses wavelengths that lie between 300 and 6.2.1 For the purposes of this practice, the difference Dl
i
2500 nm (3000 to 25000 Å). Only the portion between 380 between adjacent wavelengths (l and l ) shall be less than
i i+1
15nmforany i, Nshallbegreaterthan25,andthefirstandlast
and 760 nm is visible radiation, however. In daylighting
wavelength (l and l ) shall be within 30 nm of 380 and 760
applications, it is therefore important to distinguish the solar
1 N
nm, respectively.
radiant energy transmittance and reflectance of these materials
6.2.2 The standard spectral irradiance distribution E used
from their luminous (visual or photometric) transmittance and l
in this calculation shall be the direct normal irradiance for air
reflectance.
mass 1.5 provided in Standard Tables E891.
5.2 For comparisons of the energy and illumination perfor-
NOTE 1—The spectral distribution of CIE standard illuminant D-65 is
mancesofbuildingfenestrationsystemsitisimportantthatthe
similar to the spectral irradiance distribution provided in Tables E891.
calculation or measurement, or both, of solar radiant and
Calculations of solar photometric transmittance and reflectance of a
luminous transmittance and reflectance of materials used in
variety of different samples using the D-65 spectral irradiance values for
fenestration systems use the same incident solar spectral
...
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