Rear lights
I like Indianken's verse. I can relate to that.
A problem with LED lights I became aware of when using LED torches, is that the light seems to be very directional. There's little "scatter". This means that the LED light that is so satisfyingly bright when I squat down to look directly at it, isn't very visible (assuming she is aware that there is anyone else on the road) to the mum on the school run, 12 feet above the road, in her SUV. (SUV: the Transit van of the middle-class)
Overthehill addressed this by packing his "STOP" light with faceted reflectors, and i can testify, having followed him, to the brightness of his LED rear light. Compromises have to be made though, because the Miller shell has very little room.
Even with "the board" of dozens of LED lamps, my lamp, with no scatter except from a scratched lens, is MUCH less visible than the "squarish" Lucas tail lamp fitted to my Sunbeam S7, and to Series D Vincents. Painting the inside of the shell white helps, but what it needs is a faceted lens, instead of the plain one. Goffie please note! Please!
Overthehill also fitted an after-market-intended-for-cars LED strip screwed under the seat as a brake light, so when he braked, man, it got BRIGHT. It was like following a modern Honda. And this was in daylight, or at least the gloom of a wet Scottish summer afternoon.
(There might be a parallel here with super eco lamps that are too dim to read by, with "proper" incandescent lamps, but I don't want to go there. I've got a pot of yoghurt to knit before breakfast.)