Abstract: Method of heating by emission of electromagnetic radiation, wherein at least one emitting source is arranged extending in the form of a resistive element matching as close as possible the geometry formed by the joint lines of the thermoplastic components to be joined together with a reflecting zone conforming likewise to the profile of the resistive element, then an energy source, such as, especially, an electric current, is caused to pass inside the said emitting source so as to cause, by the Joule effect and by focusing the released radiation onto the reflective surfaces, possibly coated with a metal film, a surface layer of material at the interface of the said components to melt, and then the radiating source is set back in a position which does not interfere with the joining of the components.