ASTM E424 Test Methods for Solar Energy Transmittance and Reflectance (Terrestrial) of Sheet Materials

Scope:

ASTM E424 is a standard test technique for sheet materials’ solar energy transmittance and reflectance. There are two approaches specified in ASTM E424. Method A uses a spectrophotometer to measure both transmittance and reflectance. Furthermore, Method B utilizes a pyranometer to measure the transmittance in an enclosure with the sun as the energy source. The approaches have been found to work for both clear and translucent materials, as well as those with highly reflecting coatings that reduce transmittance. Because the transmittance is averaged across a vast area, Method B is particularly well suited to measuring the transmittance of inhomogeneous, patterned, or corrugated materials.

Test Procedure:

Two approaches are used in the ASTM E424 test procedure:

Method A: 

Throughout the spectrum range of 350 to 2500 nm, an integrating sphere spectrophotometer measures spectral transmittance or reflectance versus a magnesium oxide standard. Normal-diffuse illumination and viewing mode are required. Integrating over a conventional solar energy distribution curve using weighted or selected ordinates for the appropriate solar energy distribution yields the solar energy transmitted or reflected.

Method B:

This test method uses the sun as the source and a pyranometer as the detector. The test specimen is made to be the cover, with the plane of the specimen perpendicular to the incident radiation; transmittance is determined as the ratio of the energy transferred to the incident energy.

Specimen Size:

As per the ASTM E424 test procedure, the geometry of the spectrophotometer limits the size of specimens for Method A, whereas Method B demands a specimen with the size of 0.61 m2.

Data:

According to ASTM E424, both test techniques produce substantially identical results for the materials investigated by the drafting task group.

Conclusion: 

ASTM E424 test procedure includes two test techniques for measuring solar energy transmittance and reflectance in sheet materials.