Solar Absorptance, Reflectance and Transmittance of Materials Using Integrating Spheres
This test method covers the measurement of spectral absorptance, reflectance and
transmittance of materials using spectrophotometers equipped with integrating spheres.
It will also cover the methods used of computing solar weighted properties from
the measured spectral values.
For this test measurements of transmittance (or reflectance) are made over the spectral
range from approximately 300 to 2,500nm using an integrating sphere spectrophotometer.
The specimen can be patterned, opaque, transparent or slightly translucent and can
vary in size depending on the integrating sphere being used for measurements. The
solar absorptance can be explained in terms of a ratio where 1 is the maximum amount
of solar heat gain that can come through a skylight and 0 is the least amount. Therefore,
a solar heat gain coefficiency of 0.40 means that 40% of the available solar heat
is coming through the entire skylight unit.
During the test the 100% and zero line curves should be recorded. For reflectance
measurements, record the zero line with a perfect absorber or light trap in the
sample port. For transmittance measurements, record the zero line with the sample
beam blocked, preferably as far in front of the entrance port as convenient. Reflectance
of opaque and transparent or translucent materials is calculated differently to
each other by means of position in the integrating sphere and amount of light being
allowed to enter the sphere.