Alex wrote:

But... if the fuse to the lights blows, you'd be operating said
machinery in the dark at full speed.

Far more likely is that the socket circuit trips for some reason, and
takes supply for lights with it, so you are in the dark as machinery is
slowing down. The design will get more elaborate to achieve full
discrimination. I got the impression this a just a small shed, not a
serious workshop.

--
Andy