Light Pollution Filter Experiment

Hi,

Martin Brown recently wrote about light pollution:
It is modulated with the second harmonic whatever frequency your
local
power grid runs at 50/60Hz. But you can't do much using that.

That gave me an idea. In Sweden we have 50 Hz power grid. In my mind I
imagined that the sky was fluctuating like a stroboscope at 100 Hz. If
I could block the light when it was bright then I had made a light
pollution filter. I mounted a rotating shutter on a synchronous motor
with 1500 rpm. The shutter was a circle with a small angle opening at
every 90 degree. (Optimum is 3000 rpm motor with opening at every 180
degree) I tested the device indoors under white fluorescent light. I
saw a yellow cross! That was the light minimas! Then I tried the
device outdoors aiming it at the sky. Negative, I could not visually
detect any minimas on the sky glow or the distant lamps. Maybe it will
work photographically but I'm not going to try.

Roger Persson