In one aspect, a device is adapted to transmitting power to, or receive power from, a remote device over first and second communication lines (DALI+, DALI−) and to communicate with the remote device over the first and second communication lines. A first driver implements a first communications protocol which comprises coupling the first and second communication lines together to encode a first signal level and isolating the first and second communication lines from each other to encode a second signal level. This may be a DALI protocol. A second driver implements a second communications protocol which comprises modulating the first communication line with a signal having a low modulation depth. The second communications protocol means there is always a voltage difference between the two communication lines to enable continuous power harvesting. A second aspect relates to efficient power transfer by disabling a current limiter function, when possible.