mike ring writes:

The resultant 50Hz flicker gives a greater apparent brightness, like
strobed bike lamps for half the power dissipation!
I thought we were talking about a supply to a fan here..... not sure
what it will make of half wave DC even if the LED can cope!
Yup, way back we decided it wasn't the way to go, this is just philosophy.

Surprising that no one uses a bidirectional LED (i.e. one containing two
back-to-back diodes), so that the 100 Hz flicker isn't apparent.

They're available with both diodes being of the same colour if desired,
and not expensive.

Just add in series one of those interference-suppressor devices
(actually 0.1 uF / 250VAC with 100 ohms in series) and you've got some
protection against current surges caused by spikes on the line.

A fairly cheap, non-dimming, non-flickering substitute for a neon.

Works for me in the occasional home-built contraption; maybe some
manufacturers actually use this arrangement?

--
Roy Millar, Use m o u l i n e t @