Patent ID: 8033686

Claim:
A lighting unit comprising: a power input adapted to receive power via a power supply circuit, wherein the power supply circuit receives a supply of AC power through a switch and includes a source of DC power; at least one light emitting diode (LED) adapted to receive power via the power input; a sensor configured to generate an output indicative of an impedance associated with the power supply circuit; and a controller configured to: determine an operational state of the switch through a plurality of measurements of the sensor output; and cause DC power to be supplied to the at least one LED from the source of DC power when AC power is not present on the power input and the operational state of the switch indicates that the switch is in a closed or partially closed state, wherein the controller is further configured to: determine a first impedance value associated with the power supply circuit corresponding to an open operational state of the switch; determine a second impedance value associated with the power supply circuit corresponding to a closed operational state of the switch; establish a threshold impedance level based on the first and second impedance values; determine a third impedance value associated with the power supply circuit, when AC power is not present on the power input; and cause the DC power to be supplied to the at least one LED from the source of DC power when AC power is not present on the power input and a comparison between the third impedance value and the threshold impedance level indicates that the switch is in a closed state.