Abstract: A photoelectric control unit for street lighting comprises control means including a photoelectric sensor mounted on a printed circuit board for switching on a street lamp when the intensity of light falling on the sensor falls below a preset value. Electrical connection means between the P.C.B. and the lamp is provided by three connector pins which are led through a cooling chamber or stem. The pins are cranked to closely follow the contour of the chamber to dissipate heat through the chamber walls. The chamber is also filled with a high thermal conductivity potting compound for heat transfer to the walls of the chamber.One controller for such a photoelectric control unit includes a switching means provided by a relay and a triac connected in parallel. The triac operates to prevent the relay being subjected to high voltages during switching and hence prevents pitting of the relay contacts.