Illumination device with a light guide of a liquid-filled plastic flexible tube

An illumination device comprising a light guide including a flexible tube which consists at least at the inner side of a carbon fluoropolymer of copolymer and which is sealed at the ends by transparent terminal windows and is filled with a transparent liquid, wherein the filling liquid contains a phenylmethyl silicone oil wherein the silicone oil has valences which are saturated by molecular radicals, more than 20% of said radicals being phenyl groups.