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From: jmsulliv@phoenix.Princeton.EDU (John M. Sullivan)
Newsgroups: misc.consumers,sci.electronics
Subject: Re: fluorescent lights and my brain
Message-ID: <2814@phoenix.Princeton.EDU>
Date: 8 May 88 04:21:30 GMT
References: <530@scourge> <1182@ssc.UUCP> <1532@dataio.Data-IO.COM> <1143@neoucom.UUCP> <9890@ism780c.UUCP>
Reply-To: sullivan@fine.Princeton.EDU (John M. Sullivan)
Organization: Princeton University Department of Mathematics
Lines: 49
Keywords: eyes head ache electricity

I am posting this for my brother, Charlie Sullivan, who doesn't have
access to e-mail.  I will, however, make sure that he gets replies you
send to me at sullivan@fine.princeton.edu		John Sullivan
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I work for a company, Lutron Electronics, that makes lighting controls,
including high-frequency fluorescent ballasts and other products that can help
people who are presently unhappy with fluorescent lighting, particularly
near VDTs.

My understanding of the issue of whether or not 120 Hz flicker is visible
is that pure 120 Hz is not visible, at least not to most people, but 
that any small amount of a 60 Hz component in the fluctuation of light
level is very easily visible and annoying.  This can be caused by any
assymetry  between the two halves of the 60 Hz cycle.  60 Hz flicker
is often most visible in the ends of the lamp, as they switch
between being anodes and cathodes.  Miswired fixtures, bad lamp socket 
connections, bad lamps, and combination air conditioning vents/light
fixtures ("air handling fixtures") all contribute to increasing visible
60 Hz flicker.  The filaments in the end of the lamp are normally heated to
make them emit electrons to act as cathodes.  If one end is not heated, it will
not work as well when it is supposed to be a cathode, and the whole lamp
can act somewhat like an old vacuum tube diode, and be brighter in one
half cycle than in the other half cycle.

One product our company makes is a high-frequency fluorescent ballast
called Hi-lume.  It operates above 20 kHz so that it is inaudible.
It is also more efficient than a normal 60 Hz ballast. (The lamp itself
produces more light and less heat than it would at 60 Hz, and a 60 Hz
ballast has considerable losses in the resistance of its windings, and in
the hysteresis of the magnetic material.)  The >40 kHz pulsation of light
is much too fast to be visible.  Hi-lume is also capable of controlling
the light level from 100% to 1/2%, which is good for setting a comfortable
light level for working at VDTs.  It is available in 120 and 277 volt
versions, and for a variety of lamp types. Although there is never any
visible flicker, there is some 120 Hz variation in light level.
(The circuit was designed to do that to improve power factor.)  An
older version, identified by model numbers beginning with PCU
instead of OSPCU, has no light level fluctuation below 20 kHz.

We also have other products for controlling light level of fluorescent
lamps which can be very helpful for reducing eye-strain for VDT users.
Although Hi-lume gives the best dimming performance, other products
include such things as systems that allow using normal 60 Hz ballasts to
to minimize rewiring and installation trouble and cost on retro-fit
instaltions.

For more information you can call our hot-line at 800-523-9466 or
800-222-4509 in PA.