of infra red light emitting diodes and one or more contact elements the system is such that the or each emitter strip can interconnect with a mounting strip to form a conduit through which a power supply bus may be carried each contact element is adapted to complete an electrical connection between the power supply bus and a printed circuit board mounted behind the outwardly directed face of the emitter strip the system is easily assembled and is advantageously used to provide a source of covert illumination for security or other monitoring purposes application_number US 28864802 A description referring firstly to fig1 of the drawings which illustrates an extruded plastics mounting strip 1 of a generally u shaped section the mounting strip 1 is provided on its base 3 with fixing holes not shown through which screws or the like may be passed to secure the mounting strip 1 to a structure such as a ceiling internally projecting ribs 5 5 u2032 are provided along opposing side walls of the mounting strip 1 towards the open end of the channel section a further pair of ribs 7 7 u2032 extend along the base 3 projecting into the channel section fig2 illustrates an extruded plastics emitter strip 11 of a substantially rectangular hollow section the cover face 13 of which permits transmission of infra red radiation the hollow interior 15 of the emitter strip 11 is also generally rectangular with a pair of continuous grooves 17 17 u2032 on opposing side walls which together form a slot into which one or more pcbs not shown can be slid each of the outer side walls are provided towards its upper end with.