The properties of Reflectance and Transmittance are particularly important for glass products used in the building and transport sectors, and anywhere else the fine control over the intensity of radiation passing through specific glass thicknesses or lengths (e.g. photovoltaic panels, optical fibers, etc.) is crucial.

Transmittance and reflectance spectra are determined by spectrophotometric measurements over a wide wavelength range, generally between 300 nm (UV) and 2500 nm (NIR); for specific applications (thermal transmittance processing) the measurement can be pushed up to 50,000 nm.

From the reflectance and transmittance spectra it is also possible to calculate a series of other optical quantities, such as absorbance curves, colour point, extinction coefficient, emissivity of the glass in the solar range, thermal transmittance, etc.