>>Date: Mon, 30 Oct 2000 18:39:47 -0800 (PST)
>>From: Acer V <siddim01@xxxxxxxxxxxxxxx>
>>Subject: [OM] [ot-ish] florescent lights "blanking" at 1/60sec
>>
>>i did a few rolls of indoor office building shots (clinic) this weekend,
>>and looking over the shots, it seems that some of the overhead recessed
>>lighting fixtures seem only "half" on, that is on side lit, one side
>>dark. in shot shots, the whole fixture is dark. could it be that the
>>shutter was open during the "off" cycle of the 60Hz lamps?
>
>yup. Flouescent lights flicker at 120hz. If you set your computer moniter to
>60hz in a room lit by flourescents, it will drive you crazy. This isn't a
>problem with incandescents, since they "burn" and diminish in output only a
>very little amount during zero crossing. Flourescents operate on a different
>principle, which is ionization of a gas. This turns off immediataly and
>completely at zero crossing. You have to use a slow shutter speed of less
>than 1/60th to avoid problems. This is also true of photographing TV
>screens, etc.
>
>
>Be seeing you.
>
>Dirk Wright
Also, I believe that most fluorescent light fixtures operate such that one
bulb is on during the positive half of the voltage cycle, and the other
bulb
is on during the negative half. So each bulb flickers at 60 Hz, but the
total
flickers at 120 Hz, which is fast enough to not be too obvious in most
circumstances (except Dirk's monitor example!). This of course explains
why
some of your pictures show the lights half on.
Mark Marr-Lyon
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|