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Re: Frustrating Flicker in Fluorescents (WAS: Season misconceptions innewspaper)



Hi,
The U of AZ campus facilities people have been
replacing almost all of the light fixtures. They
are finding the money to do this by the energy
savings. The new flourescents are smaller in
diameter and called T8. The "ballast" for the T8
drive the tube at something like 20,000 HZ so
there is no noticable flicker. They are suppose
to use only about 50-70% the energy for the same
level of lighting. My twin bulbs were replaced
with singles. Their color is much better as
well. During installation only half of a hallway
was done. The part with the old lights looked
very green.

I have seen limited styles of these new T8 for
sale at Home Depot so they are available to a
homeowner.

Thanks,
Roger Haar


*****************************************************************************************
John Clement wrote:

Many fluorescents apparently now lack the actual fluorescent layer.
They emit extremely strong spectral lines, unlike older tubes which show
weaker lines. Teachers on a budget can use these to demonstrate
spectral lines rather than buying expensive gas tubes. This might
contribute to larger flicker. I wonder if the coating can be devised
which has a long enough persistence to reduce the flicker.

I would assume that movies and TV would also pose some problems, as they
have ~ a 30Hz and 24 Hz refresh rate. The modern monitors with high
refresh rates would probably be a godsend. Are the plasma screens any
better than normal screens? I have heard that there are fluorescents
with doubled frequency supplies. Are they any better?

The flicker from fluorescents should not really be a problem because
they should flicker at a 120 Hz rate on each half cycle of the 60 Hz
line frequency, well above the frequency of most monitors. This is also
well above the normally cited figures for "persistence of vision".
Incidentally, the persistence of vision idea is no longer considered to
be the reason why movies and TV give a good illusion of motion. I have
heard that there are some people who never see motion pictures as fused
continuous motion.

I have essentially a glass wall facing East on the long side of my
class, so often I do not turn on the lights. Students sometimes
complain when I do turn them on, but I have never had a student complain
about the flicker. I wonder if it is possible to be desensitized to the
problem. The mind is extremely good at filtering out unwanted things.
For example, I suffer from some tinnitus which can actually be quite
loud. When I think about it or sometimes when it is quiet or I am
trying to critically listen to certain things I notice it. However when
I am busy, reading, ... I do not notice it. Similarly, patients can
sometimes be trained to mentally block pain. If it is only in the
peripheral vision, a pair of blinders might be useful. You might find
glasses with black side wings helpful.

John M. Clement
Houston, TX

John Clement wrote:

And yes, fluorescents are the way to go, but only if they have been
well
made. One popular brand has a short lifetime and as a result is not
a
bargain according to Consumer Reports.


One other thing to consider - there are many of us whose visual
"flicker
fusion frequency" is significantly higher than average. Fluorescent
lights
that most people see as glowing steadily are constantly oscillating in
brightness in our peripheral vision. Going to a grocery store or the
local
Wal-Mart is sheer torture. I have removed the fluorescent light bulbs
in
my
office and use only incandescent lighting. I teach my classes with the
shades fully up to let in maximum sunlight. I leave only the last row
of
fluorescents on in the room. Students who really want the excess
lighting
can sit there. Surprisingly, the students adapt very quickly to the
use of
predominantly natural lighting - they now protest if someone walks
into
the
room and turns on the lights. We use whiteboards and markers, students
have
no problem seeing the class material.

Bob at PC