Lights

Just out of curiosity, will a Buck driver cope with a change in supply voltage? I'm thinking of alkaline batteries running down over time and also the possibility of replacing alkaline cells with NiMH.

Yes. Buck drivers are often used with Li-ion cells, nominally 3.7v but drive up to from 4.2V at full. The point of the buck is to keep the current constant, as LEDs aren't linear, so the output voltage can vary too.