Path: utzoo!mnetor!uunet!husc6!linus!philabs!prv
From: prv@philabs.Philips.Com (Paul Veldman)
Newsgroups: sci.electronics
Subject: Re: Fluorescent lights and my brain.
Message-ID: <3512@briar.Philips.Com>
Date: 29 Apr 88 15:57:47 GMT
Organization: Philips Laboratories, Briarcliff Manor, NY.
Lines: 40
Keywords: Flickering, fluorescent, light, lamps


I will add my $0.02:

1) There seems to be a general misunderstanding about the
   flickering of fluorescent lamps.
   Although, for mains frequency operated fluorescent lamps, the
   major part of the light ripple consists of the second harmonics
   of the mains frequency, the light ripple that annoys people
   is generally the (small) ripple at the mains frequency itself.
   In ideal lamps that component is zero, but in practice it is not.
   This phenomena is stronger with brand new lamps (that still have
   to get rid of some impurities) and lamps running towards end of life,
   where the emitter substance on the electrodes starts to get exhausted.
   In both cases it is especially noticeable around the electrode area of
   the lamp.
   It is caused by a slightly asymmetrical behavior with respect to 
   re-ignition of the lamp after zero-crossing of the current.

2) It was suggested that using a solid state ballast, which operates
   the lamp(s) in the kHz range (generally between 20 and 60 kHz) 
   eliminates any light ripple. If operated from the mains, this
   statement is only true if a large energy-buffer (generally a large
   electrolytic capacitor) is used as an intermediate stage, between
   mains input and the high frequency converter. 
   Not all solid state ballasts on the market are operated in this way,
   because there are regulations that have to be met with respect to the 
   amount of distortion in the current you draw from the mains.
   Therefore part of the designs presently on the market show a high
   frequency operation of the lamp which is amplitude and/or frequency 
   modulated with (twice) the mains frequency, resulting in a light-ripple
   of twice the mains frequency (and higher harmonics). As explained above,
   this generally does not bother people. You do however get rid of the
   light-ripple component that bothers people (at the mains frequency itself),
   because generally re-ignition of the lamp is prevented by keeping the lamp
   on during zero-crossing of the mains.

Paul Veldman

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