This document specifies a test method to measure the ultraviolet (UV) and visible (VIS) spectral transmittance in the wavelength range from 280 nm to 700 nm of coatings for wind turbine rotor blades. Single and multilayer coatings or coating systems can be tested. From the spectral transmittance the transmittance of UV, VIS and the combined UV and VIS wavelength range can be calculated. It is applicable to free coatings films or coatings applied on a UV-transparent quartz substrate.