This international standard specifies methods for measuring the transmittance and reflectance of glass used in Photovoltaic (PV) modules and provides instructions on how to calculate the effective hemispherical transmittance and reflectance of this glass. This standard is applicable to PV glasses used in PV modules, including ultra-clear patterned glass, anti-reflective coated (AR) glass, transparent conductive oxide coated (TCO) glass and other kinds of PV glass used in PV modules. These test methods are designed to provide reproducible data appropriate for comparison of results among laboratories or at different times by the same laboratory and for comparison of data obtained on different PV glasses. These test methods have been found practical for glass having both specular and diffuse optical properties.