[en] The experimental verification of the second postulate of the special relativity theory of the light velocity independence of the radiation source velocity, which has not been experimentally confirmed yet is presented. The experimental techniques are described given are. The results of direct measurements of the propagation velocity of the relativistic electron synchrotron radiation in the storage ring and comparison of times of flight of the synchrotron radiation photons under conditions of atmospheric pressure and high vacuum. The measurement results do not agree with the ballistic hypothesis of light propagation, but correspond to the second postulate of the special relativity theory