The AM 1.5 Standard Spectrum refers to exactly two standard terrestrial solar spectral irradiance spectra. The two spectra define a standard direct normal spectral irradiance and a standard total (global, hemispherical, within $$2\pi$$ steradian field of view of the tilted plane at $$38^{\circ}$$ from horizontal) spectral irradiance. The direct normal spectrum is the direct component contributing to the total global (hemispherical) spectrum. The current Standard Reference Spectra are both incorporated into a single document, ASTM G-173-03. They are available for download from NREL at this link. The figure below (from NREL) shows the extraterrestrial (AM 0), global tilted, and direct normal spectra, respectively.
