Since no make or model of the lights is mentioned, only some generalities:
* consider adding filtering in the supply line - typically a coil in series, and at each side a C to ground; the C's with good HF properties, ceramic might do well. One can buy these as "black boxes", they are sometimes called "pi-filter"s
* Install this/these filter(s) as close as possible to the (rightly!) suspect power switcher(s). It might even be useful to add such a filter at each end of the supply line - that line making a fairly effective transmitter antenna
* the Robin being wood built, check grounding. Ideally, all ground lines go to one central point - some implement that as a strip/bar of brass, others use a bolt that stacks the cable eyes terminating the various ground wires.