1. A DC-powered lighting device for placement in an external light fixture, the DC-powered lighting device comprising:a lighting unit configured to emit light in response to receiving DC power;
a connector configured to mechanically and electrically connect the DC-powered lighting device to the external light fixture;
a probing unit connected to the connector and configured to determine whether electrical power from a first external electrical power source is currently available via the connector and to provide a power-present signal having a signal value that is indicative of whether or not electrical power is currently available via the connector;
a DC-power input unit that is different from the connector and is configured to receive DC power from a second external electrical power source that is different from the first external electrical power source, and to deliver the received DC power to the lighting unit; and
a switching unit configured to allow or prevent the delivery of the DC power from the DC-power input unit to the lighting unit in dependence on the current signal value of the power-present signal,wherein the DC-power input unit comprises a DC connector for connection to the second external electrical power source, and wherein the DC connector is an Ethernet connector or a universal serial bus connector.