ASTM E971-88(1996)e1
(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
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 E903.
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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e1
Designation: E 971 – 88 (Reapproved 1996)
Standard Practice for
Calculation of Photometric Transmittance and Reflectance
of Materials to Solar Radiation
This standard is issued under the fixed designation E 971; 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.
e NOTE—Keywords were added editorially in April 1996.
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 E 772.
from Test Method E 903.
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—power emitted,
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-
E 772 Terminology Relating to Solar Energy Conversion
cates that the quantity has the sun as a source or is character-
E 891 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
E 903 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-
E 972 Test Method for Solar Photometric Transmittance of
2 ties, indicates that the property was evaluated at a specific
Sheet Materials Using Sunlight
wavelength, l, within a small wavelength interval, Dl about l.
E 1175 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, indicates the concentration of the quantity per unit
2.2 CIE Standard:
wavelength or frequency, indicated by the subscript lambda, as
L = dL/dl, at a specific wavelength. The wavelength at which
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
4. Summary of Practice
Solar, Geothermal, and Other Alternative Energy Sources and is the direct
4.1 Spectral transmittance or reflectance data between
responsibility of Subcommittee E44.05 on Solar Heating and Cooling Subsystems
and Systems.
wavelengths of 380 and 760 nm (3800 to 7600 Å), which have
Current edition approved Aug. 26, 1988. Published December 1988. Originally
published as E 971 – 83. Last previous edition E 971 – 83.
2 4
Annual Book of ASTM Standards, Vol 12.02. Available from Commission Internationale de l’Eclairage, Bureau Central de la
Annual Book of ASTM Standards, Vol 14.02. CIE, 4 Av. du Recteur Poincaré, 75-Paris, France.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 971
been obtained in accordance with Test Method E 903, are 6. Procedure
multiplied by solar spectral irradiance values provided in
6.1 Measurements—Measure spectral transmittance data
Standard Tables E891 and by the photopic spectral luminous
t(l ) or spectral reflectance data r(l ) from 380 nm to 760 nm
i i
efficiency function (see Annex A1). The resulting product is
as described in Test Method E 903.
integrated over the spectral range from 380 to 760 nm using a
6.2 Calculations—Calculate the photometric transmittance
summation procedure to approximate the integral. This sum-
t or reflectance r using Eq 1 as follows:
v v
mation procedure is then repeated with the product of the solar
N N
energy spectral distribution and the photopic spectral luminous
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 5 1 i 5 1
efficiency. The ratio of the two integrals is the solar luminous
(photometric) transmittance or reflectance of the measured
where:
sample.
E = terrestrial direct normal solar spectral irradiance for
li
air mass 1.5 provided in Tables E891,
5. Significance and Use
V = photopic spectral luminous efficiency function given
l
5.1 Glazed apertures in buildings are commonly utilized for
in Annex A1, and
the controlled admission of both light and solar radiant heat
N = number of wavelengths for which E is known
l
energy into the structure. Other devices may also be used to
between 380 nm and 760 nm.
reflect light and solar radiant heat into a building.
6.2.1 For the purposes of this practice, the difference Dl
i
5.1.1 Most of the solar radiant energy entering a building in
between adjacent wavelengths (l and l ) shall be less than
i i+1
this manner possesses wavelengths that lie between 300 and
15 nm for any i, N shall be greater than 25, and the first and last
2500 nm (3000 to 25 000 Å). Only the portion between 380
wavelength (l and l ) shall be within 30 nm of 380 and 760
1 N
and 760 nm is visible radiation, however. In daylighting
nm, respectively.
applications, it is therefore important to distinguish the solar
6.2.2 The standard spectral irradiance distribution E used
l
radiant energy transmittance and reflectance of these materials
in this calculation shall be the direct normal irradiance for air
from their luminous (visual or photometric) transmittance and
mass 1.5 provided in Standard Tables E891.
reflectance.
NOTE 1—The spectral distribution of CIE standard illuminant D-65 is
5.2 For comparisons of the energy and illumination perfor-
similar to the spectral irradiance distribution provided in Tables E891.
mances of building fenestration systems it is important that the
Calculations of solar photometric transmittance and reflectance of a
calculation or measurement, or both, of solar radiant and
variety of different samples using the D-65 spectral irradiance values for
luminous transmittance and reflectance of materials used in El above have shown a maximum difference of 0.004 in absolute
transmittance of reflectance from those calculated using the spectral
...
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