NBN EN 16795:2016

This European Standard specifies a method for estimating the temperature increase of a flat polymer surface, due to its solar radiant energy absorption, compared to the ambient temperature.
For that purpose, a specimen and black and white reference plates are exposed to simulated solar radiation under specified conditions (simulated solar radiation, ambient air temperature, convective flow). For opaque specimens, a thermally sensitive electrical element at the backside or a pyrometer is used to measure the surface temperature. For translucent specimens, a pyrometer is used to measure surface temperature.
NOTE Some specific polymeric materials are translucent (transparent) and might have a transmittance window in a wavelength range where the used pyrometer is sensitive (e.g. polyethylene). The surface temperature of these materials cannot be measured with the contact and the contactless method.