ASTM E971-11(2019)

Standard Practice for Calculation of Photometric Transmittance and Reflectance of Materials to Solar Radiation

SIGNIFICANCE AND USE
5.1 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 Å). 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.  
5.2 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.  
5.3 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 E1175 (or Test Method E972) 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 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 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.4 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.5 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.

General Information

• Status: Published
• Publication Date: 30-Sep-2019
• ICS: 27.160 - Solar energy engineering
• Technical Committee: E44 - Solar, Geothermal and Other Alternative Energy Sources
• Drafting Committee: E44.20 - Optical Materials for Solar Applications

Relations

• Replaces: ASTM E971-11 - Standard Practice for Calculation of Photometric Transmittance and Reflectance of Materials to Solar Radiation
• Effective Date: 01-Oct-2019
• Refers: ASTM E772-13 - Standard Terminology of Solar Energy Conversion
• Effective Date: 01-Sep-2013
• Refers: ASTM E772-11 - Standard Terminology of Solar Energy Conversion
• Effective Date: 01-Sep-2011
• Refers: ASTM E1175-87(2009) - Standard Test Method for Determining Solar or Photopic Reflectance, Transmittance, and Absorptance of Materials Using a Large Diameter Integrating Sphere
• Effective Date: 01-Apr-2009
• Refers: ASTM G173-03(2008) - Standard Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37° Tilted Surface
• Effective Date: 01-Jun-2008
• Refers: ASTM E972-96(2007) - Standard Test Method for Solar Photometric Transmittance of Sheet Materials Using Sunlight
• Effective Date: 01-Mar-2007
• Refers: ASTM E772-05 - Standard Terminology Relating to Solar Energy Conversion
• Effective Date: 01-Apr-2005
• Refers: ASTM G173-03e1 - Standard Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37° Tilted Surface
• Effective Date: 10-Jan-2003
• Refers: ASTM E972-96 - Standard Test Method for Solar Photometric Transmittance of Sheet Materials Using Sunlight
• Effective Date: 10-Apr-1996
• Refers: ASTM E972-96(2002) - Standard Test Method for Solar Photometric Transmittance of Sheet Materials Using Sunlight
• Effective Date: 10-Apr-1996
• Refers: ASTM E1175-87(2003) - Standard Test Method for Determining Solar or Photopic Reflectance, Transmittance, and Absorptance of Materials Using a Large Diameter Integrating Sphere
• Effective Date: 01-Jan-1996
• Refers: ASTM E903-96 - Standard Test Method for Solar Absorptance, Reflectance, and Transmittance of Materials Using Integrating Spheres (Withdrawn 2005)
• Effective Date: 01-Jan-1996
• Refers: ASTM E772-87(2001) - Standard Terminology Relating to Solar Energy Conversion
• Effective Date: 27-Feb-1987
• Refers: ASTM E772-87(1993)e1 - Standard Terminology Relating to Solar Energy Conversion
• Effective Date: 27-Feb-1987
• Referred By: ASTM G214-23 - Standard Test Method for Integration of Digital Spectral Data for Weathering and Durability Applications
• Effective Date: 01-Oct-2019

Overview

ASTM E971-11(2019), "Standard Practice for Calculation of Photometric Transmittance and Reflectance of Materials to Solar Radiation," provides a standardized methodology for calculating the luminous (photometric) transmittance and reflectance of materials. Developed by ASTM International, this standard is essential for evaluating glazing materials and reflective surfaces in the context of their interaction with both solar radiation and visible light, supporting the design and performance assessment of building fenestration systems.

The standard covers calculation procedures based on spectral radiant transmittance and reflectance data, focusing on the visible spectrum (380 to 760 nm), aligning with the solar spectral irradiance distributions commonly found in daylighting applications for buildings. The method enhances the accuracy and consistency of reporting, supporting sustainable building designs that balance daylight admission and solar control.

Key Topics

• Luminous (Photometric) Transmittance and Reflectance
  The standard details how to calculate these optical properties for materials, differentiating between total solar and visible light performance.
• Spectral Data Utilization
  Calculations are performed using spectral transmittance and reflectance data (generally obtained from ASTM E903), weighted according to terrestrial solar spectral irradiance and the CIE photopic luminous efficiency function.
• Applicable Wavelength Ranges
  The focus is on the 380 to 760 nm range, corresponding to visible light, while acknowledging solar radiation spans a broader spectrum (300–2500 nm).
• Consistency in Reporting
  ASTM E971 emphasizes the importance of using the same solar spectral irradiance in all calculations or measurements for meaningful comparisons of material performance.
• Material Suitability
  This practice is most applicable for homogeneous glazing and reflecting materials. For inhomogeneous, patterned, or corrugated sheet materials, alternative methods such as ASTM E1175 or E972 may be more appropriate.
• Reporting Requirements
  Results must include photometric transmittance or reflectance values to the nearest 0.01 (1%) and relevant test data.

Applications

• Building Fenestration Systems
  Used for the evaluation and specification of windows, skylights, clerestories, and shading devices, ensuring controlled admission of daylight and solar radiation.
• Daylighting System Design
  Essential for designers and engineers optimizing daylight penetration while minimizing unwanted heat gain, thus improving occupant comfort and energy efficiency.
• Solar Illumination System Performance
  Supports the analysis and selection of materials for solar control, enhancing both energy and visual performance of building components.
• Sustainable Architecture
  Facilitates compliance with green building standards and the LEED rating system, contributing to energy-efficient building envelopes.
• Material Development and Testing
  Assists manufacturers in characterizing and certifying the optical properties of innovative glazing and reflective materials.

Related Standards

• ASTM E903: Test Method for Solar Absorptance, Reflectance, and Transmittance of Materials Using Integrating Spheres - the primary data source for ASTM E971 calculations.
• ASTM G173: Reference Tables for Solar Spectral Irradiances, providing the standard solar spectral data required.
• ASTM E1175: Test Method for Determining Solar or Photopic Reflectance, Transmittance, and Absorptance of Materials Using a Large Diameter Integrating Sphere - suitable for materials with significant inhomogeneity or structure.
• ASTM E972: Test Method for Solar Photometric Transmittance of Sheet Materials Using Sunlight.
• CIE Standard Illuminator D65: International standard for daylight, relevant for spectral calculations.
• ASTM E772: Terminology of Solar Energy Conversion.

Keywords: photometric transmittance, photometric reflectance, solar radiation, glazing materials, daylighting, fenestration, ASTM E971, building energy performance, sustainability, visible spectrum.

Standards Content (Sample)

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:E971 −11 (Reapproved 2019)
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 E972Test Method for Solar Photometric Transmittance of
Sheet Materials Using Sunlight
1.1 This practice describes the calculation of luminous
E1175Test Method for Determining Solar or Photopic
(photometric) transmittance and reflectance of materials from
Reflectance, Transmittance, andAbsorptance of Materials
spectral radiant transmittance and reflectance data obtained
Using a Large Diameter Integrating Sphere
from Test Method E903.
2.2 CIE Standard:
1.2 Determination of luminous transmittance by this prac-
Standard Illuminator D65
tice is preferred over measurement of photometric transmit-
tance by methods using the sun as a source and a photometer
3. Terminology
as detector except for transmitting sheet materials that are
3.1 Definitions—For definitions of other terms used in this
inhomogeneous, patterned, or corrugated.
practice, refer to Terminology E772.
1.3 The values stated in SI units are to be regarded as
3.1.1 illuminance, n—luminous irradiance.
standard. No other units of measurement are included in this
3.1.2 luminous (photometric), adj—referring to a radiomet-
standard.
ric quantity, indicates the weighted average of the spectral
1.4 This standard does not purport to address all of the
radiometric quantity, with the photopic spectral luminous
safety concerns, if any, associated with its use. It is the
efficiency function given in Annex A1 being the weighting
responsibility of the user of this standard to establish appro-
function (see Appendix X1).
priate safety, health, and environmental practices and deter-
3.1.3 radiant flux,Φ = dQ⁄dt[Watt(W)],n—poweremitted,
mine the applicability of regulatory limitations prior to use.
transferred, or received in the form of electromagnetic waves
1.5 This international standard was developed in accor-
or photons. See radiometric properties and quantities.
dance with internationally recognized principles on standard-
3.1.4 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 solar, adj—(1) referring to a radiometric term, indi-
2. Referenced Documents
cates that the quantity has the sun as a source or is character-
istic of the sun. (2) referring to an optical property, indicates
2.1 ASTM Standards:
the weighted average of the spectral optical property, with the
E772Terminology of Solar Energy Conversion
solar spectral irradiance E used as the weighting function.
G173TablesforReferenceSolarSpectralIrradiances:Direct
sλ
Normal and Hemispherical on 37° Tilted Surface
3.1.6 spectral, adj—(1) for dimensionless optical
E903Test Method for Solar Absorptance, Reflectance, and
properties, indicates that the property was evaluated at a
Transmittance of Materials Using Integrating Spheres
specific wavelength, λ, within a small wavelength interval, ∆λ
about λ. Symbol wavelength in parentheses, as L (350 nm,
3500Å), or as a function of wavelength, symbol L(λ). (2) for a
These test methods are under the jurisdiction of ASTM Committee E44 on
radiometric quantity, indicates the concentration of the quan-
Solar, Geothermal and Other Alternative Energy Sources and is the direct respon-
sibility of Subcommittee E44.20 on Optical Materials for Solar Applications.
tity per unit wavelength or frequency, indicated by the sub-
Current edition approved Oct. 1, 2019. Published October 2019. Originally
script lambda, as L = dL/dλ, at a specific wavelength. The
λ
approved in 1983. Last previous edition approved in 2011 as E971–11. DOI:
wavelength at which the spectral concentration is evaluated
10.1520/E0971-11R19.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on AvailablefromCommissionInternationaledel’Eclairage,BureauCentraldela
the ASTM website. 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
E971−11 (2019)
may be indicated by the wavelength in parentheses following inhomogeneities or corrugations in the sample must not be
the symbol, L (350 nm). large. Test Method E1175 (or Test Method E972) is available
λ
for sheet materials that do not satisfy this criterion.
4. Summary of Practice
6. Procedure
4.1 Spectral transmittance or reflectance data between
6.1 Measurements—Measure spectral transmittance data
wavelengths of 380 and 760 nm (3800 to 7600 Å), which have
τ(λ) or spectral reflectance data ρ(λ) from 380 nm to 760 nm
i i
been obtained in accordance with Test Method E903, are
as described in Test Method E903.
multiplied by solar spectral irradiance values provided in
Standard Tables G173 and by the photopic spectral luminous 6.2 Calculations—Calculate the photometric transmittance
efficiency function (see Annex A1). The resulting product is τ or reflectance ρ using Eq 1 as follows:
v v
integrated over the spectral range from 380 to 760 nm using a
N N
ρ orτ 5 ρ λ orτ λ ·E V ∆λ / E V (1)
summation procedure to approximate the integral. This sum- S @ ~ ! ~ !# D
v v i i λi λi i λi λi
( (
i51 i51
mation procedure is then repeated with the product of the solar
where:
energyspectraldistributionandthephotopicspectralluminous
efficiency. The ratio of the two integrals is the solar luminous
E = terrestrialdirectnormalsolarspectralirradianceforair
λi
(photometric) transmittance or reflectance of the measured mass 1.5 provided in Tables G173,
sample. V = photopic spectral luminous efficiency function given
λ
in Annex A1, and
5. Significance and Use
N = number of wavelengths for which E is known be-
λ
tween 380 nm and 760 nm.
5.1 Glazed apertures in buildings are commonly utilized for
the controlled admission of both light and solar radiant heat
6.2.1 For the purposes of this practice, the difference ∆λ
i
energy into the structure. Other devices may also be used to
between adjacent wavelengths (λ and λ ) shall be less than
i i+1
reflect light and solar radiant heat into a building.
15nmforany i, Nshallbegreaterthan25,andthefirstandlast
5.1.1 Most of the solar radiant energy entering a building in
wavelength (λ and λ ) shall be within 30 nm of 380 and 760
1 N
this manner possesses wavelengths that lie between 300 and
nm, respectively.
2500 nm (3000 to 25000 Å). Only the portion between 380
6.2.2 The standard spectral irradiance distribution E used
λ
and 760 nm is visible radiation, however. In daylighting
in this calculation shall be the direct normal irradiance for air
applications, it is therefore important to distinguish the solar mass 1.5 provided in Standard Tables G173.
radiant energy transmittance and reflectance of these materials
NOTE 1—The spectral distribution of CIE standard illuminant D-65 is
from their luminous (visual or photometric) transmittance and
similar to the spectral irradiance distribution provided in Tables G173.
reflectance.
Calculations of solar pho
...