Sensor Head Fitted with a conical, UV stable, impact resistant, translucent cover Omni-directional NEMA connection Replacement for sensors using NEMA Rotaloc Socket Daylight Lighting Controllers These controllers automatically turn lights 'ON' and 'OFF' in response to changes in ambient light levels, primarily the transition from day to night and vice-versa. The more advanced types (see note below) have inbuilt logic to minimise false triggering, whereas the remainder have inbuilt time delays or higher 'OFF' thresholds, to prevent on/off cycling. As a general rule, these controllers should be sited such that they are not illuminated, by the light they are controlling. Nominal supply voltage is 230Vac.,Note regarding energy-saving negative-hysteresis controllers,Where figures for the 'OFF' threshold are lower than for the 'ON' threshold, the sensor is designed such that four thresholds are actually monitored. These are: dusk, the middle of the night, dawn and the middle of the day. Monitoring at times other than dusk and dawn enables the sensor to determine what it should be looking for next, minimising false triggering and improving overall controller operation.