Xref: utzoo misc.consumers:4772 sci.electronics:2898
Path: utzoo!mnetor!uunet!husc6!bloom-beacon!tut.cis.ohio-state.edu!osu-cis!att!att-ih!ihnp4!ihlpf!straka
From: straka@ihlpf.ATT.COM (Straka)
Newsgroups: misc.consumers,sci.electronics
Subject: Re: fluorescent lights and my brain
Message-ID: <4608@ihlpf.ATT.COM>
Date: 2 May 88 18:10:38 GMT
References: <530@scourge> <1182@ssc.UUCP> <1532@dataio.Data-IO.COM> <1143@neoucom.UUCP> <2427@ttidca.TTI.COM>
Reply-To: straka@ihlpf.UUCP (55223-Straka,R.J.)
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 33
Keywords: eyes head ache electricity

In article <2427@ttidca.TTI.COM> hollombe@ttidcb.tti.com (The Polymath) writes:
>In article <1143@neoucom.UUCP> wtm@neoucom.UUCP (Bill Mayhew) writes:
>}to be sure.  It would appear that fluorescent lights flash 120
>
>All of the above is overlooking a rather important physiological point.
>According to my psych. course in Sensation and Perception, under ideal
>circumstances the maximum flicker rate detectable by the typical human eye
>is about 60 hz.  That's why projectors in movie theaters open and close
>
>Therefore, if fluorescent tubes strobe at 120 Hz, they can't be causing
>your headache problems.  Your eyes are physiologically incapable of
>detecting the flicker.

Everyone seems to be missing this one!  To my understanding (and as an EE,
not as a human-factors type), this flicker is caused not by the 60 (or 120)
Hz of the fluorescent lights themselves, or the terminal/computer itself, but
the ALIASING of the two frequencies.

It seems that the human eye keys on the most significant stimulation that it
encounters (sort of like capture ratio, in FM radio terms).  For example,
take a MacIntosh (black on white screen, of course (~66Hz refresh)), and put
it far away from you in an environment rich in fluorescent lighting.  If you
are more than ~10 feet from the Mac, the fluorescent lights seem to dominate
your eyes, and you see some sort of odd flickering.  However, if you get close
to the Mac, say 2-3 feet, the flicker seems to disappear.  I believe that the
"capture ratio" phenomenon is what's at work here.

Since the light on most computers is white on black, one's eyes don't seem to
key on them.  The flicker issues are much different for them.
-- 
Rich Straka     ihnp4!ihlpf!straka

Advice for the day: "MSDOS - just say no."