A process and device are disclosed for carrying out continuous photoreactions in turbid, coloured or UV-absorbing media. In order to increase photon yield when carrying out continuous photoreactions in liquid substances, the liquid that flows down the vertical inner wall of a pipe (2) is scraped perpendicularly to its flowing direction by distributing rollers (4) that rotate on bars (1) of a cage-shaped rotor, and is lighted from the middle of the pipe by means of a rod-shaped photolamp (3). A liquid film of defined thickness is thus generated on the pipe wall, and catalyst layers (42) immobilised on the pipe wall or the distributing rollers (4) or reaction promoting gasses introduced inside the pipe (2) act on said liquid film. The invention is useful for photochemically purifying media that contain chlorocarbons, chlorofluorocarbons and fluorocarbons, for conditioning drinking water and super clean water.