Solar spectra in ASTM E903 solar reflectance calculations

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    • ASTM E891 is withdrawn and the same data set is available in ISO 9845-1.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    • Similarly, ASTM E892 is withdrawn and the data set is availble in ISO 9845-1.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).

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