Power Grid Blanking Filter

If much of the light pollution is from arc lighting, then there might
be pulsation synchronized with the 60 Hz power grid. It might be
possible to use a synchronized LCD panel as an effective filter.

"Stephen G. Giannoni" wrote in message
...
If much of the light pollution is from arc lighting, then there might
be pulsation synchronized with the 60 Hz power grid. It might be
possible to use a synchronized LCD panel as an effective filter.
Unfortunately, you are unlikely to have much observing time left through
such a filter... The problem is that an arc light on 60Hz, flickers once for
each half cycle (120Hz), and normally is not only 'on' at the peak of the
cycle, but the whole time while the voltage is high enough (normally perhaps
half or more of each half cycle). Then lights along a road, or on industrial
buildings, are not all on one mains phase, but are arranged to keep the
loading on the phases reasonably even. The result, is that there may be a
small amount of flicker in intensity at 360Hz, but there is light more or
less continuously... :-(

Best Wishes

Roger Hamlett wrote:

"Stephen G. Giannoni" wrote in message
...
If much of the light pollution is from arc lighting, then there might
be pulsation synchronized with the 60 Hz power grid. It might be
possible to use a synchronized LCD panel as an effective filter.
Unfortunately, you are unlikely to have much observing time left through
such a filter... The problem is that an arc light on 60Hz, flickers once for
each half cycle (120Hz), and normally is not only 'on' at the peak of the
cycle, but the whole time while the voltage is high enough (normally perhaps
half or more of each half cycle). Then lights along a road, or on industrial
buildings, are not all on one mains phase, but are arranged to keep the
loading on the phases reasonably even. The result, is that there may be a
small amount of flicker in intensity at 360Hz, but there is light more or
less continuously... :-(

Best Wishes

A co-worker told me that he looked through a wheel strobe

Roger Hamlett wrote:

"Stephen G. Giannoni" wrote in message
...
If much of the light pollution is from arc lighting, then there might
be pulsation synchronized with the 60 Hz power grid. It might be
possible to use a synchronized LCD panel as an effective filter.
Unfortunately, you are unlikely to have much observing time left through
such a filter... The problem is that an arc light on 60Hz, flickers once for
each half cycle (120Hz), and normally is not only 'on' at the peak of the
cycle, but the whole time while the voltage is high enough (normally perhaps
half or more of each half cycle). Then lights along a road, or on industrial
buildings, are not all on one mains phase, but are arranged to keep the
loading on the phases reasonably even. The result, is that there may be a
small amount of flicker in intensity at 360Hz, but there is light more or
less continuously... :-(

Best Wishes

ascope from
Mt wilson down across the LA. area at night. His comment was that he
expected to see the 120 hz phase distribution like patch work due
to capacitor networks used to maximize the power transmission.
If I recall, the 120 Hz flicker was not as broken up as he thought it would.
it would be easy to built such device that would allow you to see the sky
flicker. Years ago I participated in a measurement of the crab pulsar
optical spectra with a strobe disk in front of the spectrograph. you could
adjust the frequency and phase and thus see the pulsar on the tv camera
monitor pulse. I commented that we were guiding in 4 dimensions
as we needed to guide in ra, and dec, occasionally focus, and strobe wheel
frequency.

Dan

SG
From: Stephen G. Giannoni
SG
Subject: Power Grid Blanking Filter
SG
Date: Sat, 12 Jul 2003 12:22:31 GMT
SG
Organization: EarthLink Inc. -- http://www.EarthLink.net
SG
SG If much of the light pollution is from arc lighting, then there might
SG be pulsation synchronized with the 60 Hz power grid. It might be
SG possible to use a synchronized LCD panel as an effective filter.

The other chap had most of the reasons this will not work. Two
thers come to mind. First, the arc lighting (the 'vapor lamps' are
tied to different pairs of the three-phase mains. On a particular
street, they may fire in sequence from each pair. Blaming out one
lamp, may simply loet light from other nearby ones come thru.
The other is that, and I think you were joking a bit, an LCD
screen is hardly an optical window at all. Even by direct eye, it is a
diffusing window of no use for stargaxing.
The lad who mentioned a wheel strobe hit on an idea that I heard
of, and reported on, some years ago. A home astronomer was arriving at
an airport on a orioeller plane. Out of his window he saw the twon
beneath him thru the spinning prop baldes. Lo! He noticed that at
certain instants, a lot o the lights seen thru the blades were blanked
out. He sussed out that the baldes intercepted these lamps during
their firing phase.
Hence, he tried to build a chopper filter to fit on front of his
scope to duplicate the propeller effect. He gave up rom the mechanics
of the project.

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