On Wed, 11 Dec 2019 22:42:42 +0000, Steve Walker
wrote:

snip

At least a dynamo ensures that you have lighting when you unexpectedly
need it.

Unless you are stopped (without the battery addon). ;-)

You can be sure that rechargeable lights are flat at that point.

Not if you are a responsible road user they aren't.

Just a thought - with the low power requirements of modern LED lighting,
it should be possible to design a dynamo that delivers enough for them,
without much physical load.

They do.

Magnetic points around the wheel-rim and a
coil mounted on the frame would eliminate all mechanical losses -

But turn your bike into a scrap / nail gun. ;-(

I know
they (used to?) do hub mounted dynamos,

Do.

but the faster linear speed of
the wheel-rim would be better.

Given you can easily and quickly wear out the average cyclist by
fitting some higher wattage lamps on a conventional / traditional hub
dynamo (don't ask me how I know g), I'm not sure (ITRW) the
efficiency is a particular issue.

https://www.cyclingabout.com/dynamo-...g-lab-testing/

Cheers, T i m