One day I’ll give up on the illusion that I actually might post something useful here.
Thanks to MonkeySailor. over Christmas I did had an Arduino and some lights.
But there are loads of tutorials for it (like: http://www.instructables.com/id/Arduino-Controlled-LED-Strip-Holiday-Lighting/ ) , so there’s no point in me trying to document it.
Perhaps it’s time for the shed to have some nice lighting. Or to investigate a Raspberry PI.