Various solar spectra (i.e. solar spectral irradiance distributions) could be used in solar reflectance (of course, solar transmittance and absorptance too) calculations according to ASTM E903, as listed below:
- ASTM E891:
- Default solar spectrum used by the building industry and by OTM in SRI testing.
- It is the default solar spectrum due to historical reasons and for compatibility with existing practices, data and instruments.
- ASTM E891 is withdrawn and the same data set is available in ISO 9845-1.
- ASTM E892:
- Default solar spectrum for solar reflectance testing of non-roofing materials, according to LEED (note: solar reflectance only, not SRI)
- Similarly, ASTM E892 is withdrawn and the data set is availble in ISO 9845-1.
- ASTM E891 and E892 are different. ASTM E891 is in terms of direct normal solar radiation (no diffuse radiation); ASTM E892 is in terms of hemispherical solar radiation (with diffuse radiation).
- ASTM G173:
- Default solar spectrum included in ASTM E903, including both direct normal solar spectrum (equivalent to ASTM E891) and hemispherical solar spectrum (equivalent to ASTM E892)
- It is not often used in the buidling industry, due to the historical reasons stated under ASTM E891.
- ASTM E490:
- Used in extraterrestrial applications, with AM0.
- All other spectra mentioned above are with AM1.5 (refer to this article on air mass).