This document provides an appropriate reference spectral irradiance distribution to be used in determining relative performance of solar thermal, photovoltaic, and other systems, components and materials where the direct or hemispherical irradiance component is desired. This document provides one reference hemispherical irradiance spectrum, one reference direct normal irradiance spectrum and 171 subordinate hemispherical tilted irradiance spectra. The reference spectral irradiance presented in this document defines an air mass 1,5 solar spectral irradiance, for use in solar applications where a reference spectral irradiance is required, for the direct normal radiation 5,8° field-of-view angle and hemispherical radiation on an equator-facing, 37° tilted plane for albedo corresponding to a light sandy soil. The reference spectral irradiance  are intended to represent ideal clear sky conditions. The reference spectra and the subordinate spectral irradiances representing different sky conditions are provided in .xls files available at https://standards.iso.org/iso/9845/-1/ed-2/en/