Leviton's photocells are sensors used to precisely monitor either task or ambient light levels. As part of a Leviton lighting control system, photocells work with other components in the system to automatically adjust light levels to a user defined level. The photocell is most suitable for installation in rooms with windows and open spaces receiving substantial ambient light. Photocells must be hardwired to a compatible Leviton lighting control system. The photocell measures ambient light in a specific area and sends this data to a dimmer or relay that, in turn, adjusts fixtures to a constant lighting level as measured in that specific area. This is called daylight harvesting when lights in a room (with windows or significant, artificial ambient light) will automatically brighten or dim depending on how much light the photocell detects. Either surface mount or ceiling.