A combination (110) of a light bulb (111) and a bulb holder (112) in which the light bulb (111) comprises a plurality of light emitting diodes (77) mounted on a mounting platform (76) located within a globe (74) of the light bulb (111). The mounting platform (76) is mounted on and in heat conducting engagement with a heat transfer member (75) which is located within and in heat conducting engagement with an Edison screw threaded first coupling element (73) also of heat conductive material, so that heat generated by the light emitting diodes (77) is conducted through the mounting platform (76), the heat transfer member (75) and the first coupling element (73) into the light bulb holder (112). The light bulb holder (112) comprises a body member (93) of heat conductive material having an internally Edison screw threaded socket (95) engageable with the first coupling element (73) of the light bulb (111). A plurality of heat exchange fins (97) extending outwardly from the body member (93) sink heat conducted from the light bulb (111) into the light bulb holder (112). Concentric contact elements (115,116) located at the end of the first coupling elements (73) are engageable with corresponding concentric first and second contact elements (121,122) located in the socket (95) for providing an electrical power supply to the light emitting diodes (77).