The pyrgeometer LP PIRG 01 is based on a thermopile sensor whose surface is coated with black opaque varnish that allows the instrument to not be selective towards the different wavelengths. The sensor is covered by a silica window which has two fundamental objectives:
1- Protect the thermopile from bad weather;
2- Determine the spectral range of the instrument: the silica is transparent for the major wavelengths of 1.1um; it's only on the inside from the window a filter is placed to block the radiation up to 4.5-5 μm. The
outer surface of the silica, which is exposed to atmospheric agents, is coated with an anti-scratch coating (DLC) to ensure strength and duration in all climatic conditions. Anti-scratch coating cleans the surface without danger of scratching the window. The transmission of the silica window at different wavelengths is shown in the