ASTM E424-71(2001)

Standard Test Methods for Solar Energy Transmittance and Reflectance (Terrestrial) of Sheet Materials

SCOPE
1.1 These test methods cover the measurement of solar energy transmittance and reflectance (terrestrial) of materials in sheet form. Method A, using a spectrophotometer, is applicable for both transmittance and reflectance and is the referee method. Method B is applicable only for measurement of transmittance using a pyranometer in an enclosure and the sun as the energy source. Specimens for Method A are limited in size by the geometry of the spectrophotometer while Method B requires a specimen 0.61 m (2 ft). For the materials studied by the drafting task group, both test methods give essentially equivalent results.
1.2 This standard does not purport to address all of the safety problems, 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.

General Information

• Status: Historical
• Publication Date: 14-Apr-1971
• ICS: 83.140.10 - Films and sheets
• Technical Committee: E44 - Solar, Geothermal and Other Alternative Energy Sources

Relations

• Replaced By: ASTM E424-71(2007) - Standard Test Methods for Solar Energy Transmittance and Reflectance (Terrestrial) of Sheet Materials
• Effective Date: 01-Mar-2007
• Referred By: ASTM G214-23 - Standard Test Method for Integration of Digital Spectral Data for Weathering and Durability Applications
• Effective Date: 15-Apr-1971
• Referred By: ASTM E903-20 - Standard Test Method for Solar Absorptance, Reflectance, and Transmittance of Materials Using Integrating Spheres
• Effective Date: 15-Apr-1971
• Referred By: ASTM D4851-07(2019)e1 - Standard Test Methods for Coated and Laminated Fabrics for Architectural Use
• Effective Date: 15-Apr-1971

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E 424 – 71 (Reapproved 2001)
Standard Test Methods for
Solar Energy Transmittance and Reflectance (Terrestrial) of
Sheet Materials
This standard is issued under the fixed designation E 424; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 3.2 solar admittance—solar heat transfer taking into ac-
count reradiated and convected energy.
1.1 These test methods cover the measurement of solar
3.3 solar energy— for these methods the direct radiation
energytransmittanceandreflectance(terrestrial)ofmaterialsin
from the sun at sea level over the solar spectrum as defined in
sheet form. MethodA, using a spectrophotometer, is applicable
3.2, its intensity being expressed in watts per unit area.
for both transmittance and reflectance and is the referee
3.4 solar reflectance—the percent of solar radiation (watts/
method. Method B is applicable only for measurement of
unit area) reflected by a material.
transmittance using a pyranometer in an enclosure and the sun
3.5 solar spectrum— for the purposes of these methods the
as the energy source. Specimens for Method A are limited in
solar spectrum at sea level extending from 350 to 2500 nm.
size by the geometry of the spectrophotometer while Method B
2 2
3.6 solar transmittance—the percent of solar radiation
requires a specimen 0.61 m (2 ft ). For the materials studied
(watts/unit area) transmitted by a material.
by the drafting task group, both test methods give essentially
equivalent results.
4. Summary of Methods
1.2 This standard does not purport to address all of the
4.1 Method A—Measurements of spectral transmittance, or
safety problems, if any, associated with its use. It is the
reflectance versusamagnesiumoxidestandard,aremadeusing
responsibility of the user of this standard to establish appro-
anintegratingspherespectrophotometeroverthespectralrange
priate safety and health practices and determine the applica-
from350to2500nm.Theilluminationandviewingmodeshall
bility of regulatory limitations prior to use.
be normal-diffuse or diffuse-normal. The solar energy trans-
2. Referenced Documents mitted or reflected is obtained by integrating over a standard
solar energy distribution curve using weighted or selected
2.1 ASTM Standards:
ordinates for the appropriate solar-energy distribution. The
E 259 Practice for Preparation of Pressed Powder White
distribution at sea level, air mass 2, is used.
Reflectance Factor Transfer Standards for Hemispherical
4.2 Method B—Using the sun as the source and a pyranom-
Geometry and Bi-Directional Geometries
eter as a detector the specimen is made the cover of an
E 275 Practice for Describing and Measuring Performance
enclosure with the plane of the specimen perpendicular to the
of Ultraviolet, Visible, and Near-Infrared Spectrophotom-
3 incident radiation; transmittance is measured as the ratio of the
eters
energy transmitted to the incident energy. (The apparatus of
E 284 Terminology of Appearance
Method B has been used for the measurement of solar-energy
E 308 Practice for Computing the Colors of Objects by
reflectance but there is insufficient experience with this tech-
Using the CIE System
nique for standardization at present.)
3. Terminology Definitions
5. Significance and Use
3.1 solar absorptance—the ratio of absorbed to incident
5.1 Solar-energytransmittanceandreflectanceareimportant
radiant solar energy (equal to unity minus the reflectance and
factors in the heat admission through fenestration, most com-
transmittance).
monly through glass or plastics. (SeeAppendixAppendix X3.)
These methods provide a means of measuring these factors
These test methods are under the jurisdiction of ASTM Committee E44 on
under fixed conditions of incidence and viewing. While the
Solar, Geothermal, and Other Alternative Energy Sources and is the direct
data may be of assistance to designers in the selection and
responsibility of Subcommittee E44.05 on Solar Heating and Cooling Subsystems
and Systems. specification of glazing materials, the solar-energy transmit-
Current edition approved April 15, 1971. Published June 1971.
tance and reflectance are not sufficient to define the rate of heat
Annual Book of ASTM Standards, Vol 06.01.
transfer without information on other important factors. The
Annual Book of ASTM Standards, Vol 03.06.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 424 – 71 (2001)
methods have been found practical for both transparent and It is recommended that a freshly coated sphere be used
translucent materials as well as for those with transmittances especially when measuring translucent or specularly reflecting
reduced by highly reflective coatings. Method B is particularly specimens.
suitable for the measurement of transmittance of inhomoge- 6.3 Calibration:
neous, patterned, or corrugated materials since the transmit- 6.3.1 Photometric— The calibration of the photometric
tance is averaged over a large area. scale shall be done as recommended by the manufacturer. It
shall be carefully executed at reasonable time intervals to
6. Method A—Spectrophotometric Method
ensure accuracy over the entire range.
6.3.2 Wavelength—Periodic calibrations should be made of
6.1 Apparatus:
the wavelength scales. Procedures for wavelength calibration
6.1.1 Spectrophotometer—An integrating sphere spectro-
may be found in Recommended Practice E 275. A didymium
photometer, by means of which the spectral characteristics of
filter has also been used for this purpose. Although the
the test specimen or material may be determined throughout
absorption peaks have been defined for specific resolution in
the solar spectrum. For some materials the spectrum region
the visible spectrum it also has peaks in the near infrared;
from 350 to 1800 nm may be sufficient. The design shall be
however, the wavelength of the peaks must be agreed upon,
such that the specimen may be placed in direct contact with the
using a specific instrument.
sphere aperture for both transmission and reflection, so that the
6.4 Procedure:
incident radiation is within 6° of perpendicularity to the plane
6.4.1 Transmittance— Obtain spectral transmittance data
of the specimen.
relative to air. For measurement of transmittance of translucent
6.1.2 Standards:
specimens, place freshly prepared matched smoked MgO
6.1.2.1 For transmitting specimens, incident radiation shall
surfaces at the specimen and reference ports at the rear of the
be used as the standard relative to which the transmitted light
sphere (Note 1). The interior of the sphere should be freshly
is evaluated. Paired reflecting standards are used, prepared in
coated with MgO and in good condition.
duplicate as described below.
6.1.2.2 For reflecting specimens, use smoked magnesium
NOTE 1—Magnesium oxide standards may be considered matched if on
oxide (MgO) as a standard as the closest practicable approxi-
interchanging them the percent reflectance is altered by no more than 1 %
mation of the completely reflecting, completely diffusing at any wavelength between 350 and 1800 nm.
surface for the region from 300 to 2100 nm. The preferred
6.4.2 Reflectance— Obtain spectral directional reflectance
standard is a layer (at least 2.0 mm in thickness) freshly
data relative to MgO. Include the specular component in the
prepared from collected smoke of burning magnesium (Rec-
reflectance measurement. Back the test specimen with a black
ommend Practice E 259). Pressed barium sulfate (BaSO)or
diffuse surface if it is not opaque. Depending on the required
MgO are not recommended because of poor reflecting proper-
accuracy, use the measured values directly or make corrections
ties beyond 1000 nm.
for instrumental 0 and 100 % lines (see Method E 308).
6.1.3 Specimen Backing for Reflectance Measurement—
6.5 Calculation— Solar energy transmittance or reflectance
Transparent and translucent specimens shall be backed by a
is calculated by integration. The distribution of solar energy as
light trap or a diffusing black material which is known to 6
reported by Parry Moon for sea level and air mass 2 shall be
absorbthenearinfrared.Thebackingshallreflectnomorethan
used.
1 % at all wavelengths from 350 to 2500 nm as determined
6.5.1 Weighted Ordinates—Obtain the total solar energy
using the spectrophotometer.
transmittance, T , and reflectance, R , in percent, by integrat-
se se
6.2 Test Specimens:
ing the spectral transmittance (reflectance) over the standard
6.2.1 Opaque specimens shall have at least one plane
solar energy distribution as follows:
surface; transparent and translucent specimens shall have two
l5 2100 nm
T or R 5 ( T ~or R ! 3 E (1)
surfaces that are essentially plane and parallel. se se l5 350nm l l l
6.2.2 Comparison of translucent materials is highly depen-
El for air mass 2, at 50-nm intervals, normalized to 100, is
dent on the geometry of the specific instrument being used. It
given in Appendix X1.
is recommended that the specimen be placed in direct contact
6.5.1.1 This integration is easily programmed for automatic
with the sphere to minimize and control loss of scattered
computation.
radiation.
6.5.2 Selected Ordinates—Integration is done by reading
6.2.3 For specularly reflecting specimens the sphere condi-
the transmittance or reflectance at selected wavelengths and
tions, especially where the reflected beam strikes the sphere
calculating their average. Appendix X2 lists 20 selected ordi-
wall, shall be known to be highly reflecting (95 % or higher).
nates for integration.
6.6 Report—The report shall include the following:
6.6.1 Complete identification of the material tested, and
whether translucent, clear, or specularly reflecting,
The Beckman DK-2 Recording Spectrophotometer available from Beckman
Instruments, Inc., Fullerton, CAand the Cary 14 and 17 Recording Spectrophotom-
eter available from Varian Assoc., Palo Alto, CA, have been found satisfactory for
this purpose. For additional apparatus specifications see Recommended Practice
E 308. Journal of the Franklin Institute, Vol 230, 1940, p. 583, or Smithsonian
A piece of velvet sprayed with Nextel velvet coating 101-C10 Black available Physical Tables, Table 1, Vol 815, 1954, p. 273.
from 3M Company; Parson’s Black available from Eppley Laboratories, Newport, Olson,O.H.,“SelectedOrdinatesforSolarAbsorptivityCalculations,” Applied
RI or Krylon Flat Black have been found satisfactory for this purpose. Optics, Vol 2, No. 1, January 1963.
...