we say: almost 99% UV protective
Diasec offers a large protection against the damaging effect of UV radiation.
The whole spectrum of visible and invisible light contains radiation that causes the breakdown of pigment and colour. The invisible ultra-violet spectrum contains the largest amount of harmful radiation. Therefore, it is important to filter this part of the radiation.
The general property of plexiglas is that it is 99% UV protective. We always work with the best quality of plexiglas available.
The Instituut Collectie Nederland (Cultural Heritage Agency of the Netherlands, part of the State Department for Cultural Heritage) has conducted interesting studies by order of the Ministry of OCW (Education, Culture, and Science) into, among others, the reduction of light damage to museological objects.
Museums and galleries work with the guidelines of this institute. There are interesting studies by order of the Ministry of OCW. If you are interested, read a pdf of the Rijksdienst voor het Cultureel Erfgoed (In Dutch) about the restriction of pigment damage by radiation.