Wasn't it Mark Ayliffe who wrote:
On or about 2007-10-19,
Mike Williams illuminated us with:
Wasn't it Les Hemmings who wrote:

Well, LED's only work with one polarity (all diodes work like a one way
valve, letting current flow one way but not the other) so on alternating
current they will flicker at the same frequency as the mains (50 Hz in the
UK i think) which means there are 25 periods of darkness per second.

I'd guess that they'll probably use flicker-free LED lights for street
lighting. Such things do exist. Some people (e.g. me) find the flicker
from LEDs extremely annoying. I find it painful to look at the new LED
traffic lights that have been installed around here, and would go
bananas if whole streets were lit that way.

By the way: 50Hz would mean 50 periods of darkness per second, not 25.

Errm, sorry to be a paid, but wouldn't it be 100? 2 zero crossings per
cycle, no?

No. All diodes work like a one-way valve, letting current flow one way
but not the other. So they're dark for the whole half cycle where the
current flows in the opposite direction.

I guess one way to make flicker free LED lights would be to use pairs of
LEDs arranged with opposite polarity, so that both half cycles are used.

I also guess that for street lights, they'd be using "white" LEDs. The
way most "white" LEDs work is that the LED itself actually emits blue
light, but it is coated with a phosphor that absorbs some of that blue
light and fluoresces with a broad spectrum yellow light. The blue and
yellow give the appearance of white light, with loss of colour fidelity
in the red and green. The fluorescence effect lags behind the light
emitted from the LED.

--
Mike Williams
Gentleman of Leisure