RE: Connectix QuickCam problem

chuck elliot (C.Elliot@shu.ac.uk)
Thu, 04 Apr 1996 10:57:42 +0000


Actually, although the current flowing through the filament
alternates and therefore reaches a zero value twice in each
a/c cycle, as the light is produced by the temperature of the
filament and not directly by the presence of current, the filament
would have to cool to a temperature at which light is not emitted
in the time it takes to switch polarity of current, to get flicker. This
period is
about 1/200th of a second - if that's enough time to cool then there
will be flicker, if not, light is produced more or less continuously.

You can test this by blinking at a rate of approx 100 times/sec
in sync with the a/c supply thus effectively turning the light out
(if what you said was true). ;o)

Chuck.

At 18:23 04/04/96 +-1000, you wrote:
>Bzzzzt...wrong...thanks for playing.
>
>To be perfectly correct, unless one's incandescent lights are
>connected to a DC power source, they are turning on and off
>at whatever your AC powersource's line frequency is (60 Hz in
>the States, 50 Hz here in Australia).
>
>It only -looks- continuous to the human eye. To the degree that a
>a camera is sensitive to light transitions is the extent to which
>flicker will be faithfully reproduced.
>
>John
>
>
>----------
>From: wcw@bga.com[SMTP:wcw@bga.com]
>Sent: Thursday, 4 April 1996 4:54
>To: CU-SEEME-L@cornell.edu
>Subject: Re:Connectix QuickCam problem
>
>>Date: Wed, 03 Apr 1996 07:56:35 -0500
>>Reply-To: Bill.Robertson@crc.doc.ca
>>Sender: owner-CU-SEEME-L@cornell.edu
>>From: Bill Robertson <Bill.Robertson@crc.doc.ca>
>>To: <CU-SEEME-L@cornell.edu>
>>Subject: Connectix QuickCam problem
>>X-Sender: bill@mars.dgrc.doc.ca
>>X-PH: V4.1@cornell.edu (Cornell Modified)
>>X-Listprocessor-Version: 7.2(a) -- ListProcessor by CREN
>>
>>First off this is a problem with my 2 QuickCams not CUSeeMe.
>>
>>I posted here because I couldn't find another place to post.
>>I'd appreciate it if anyone could suggest a better list or newsgroup
>>to post to.
>>
>>The problem with both my QuickCams is how they behave under fluorescent
>>light vs. incandescent or natural light. Under fluorescent light, with a
>>well lit static scene and brightness set to automatic or manual (under
>>either QuickMovie or CUSeeMe), the captured video continuously fluctuates
>>getting brighter and dimmer about once per second. Under incandescent or
>>natural light the problem disappears and the brightness of the captured
>>video remains constant.
>>
>>Have I got 2 bad cameras? Is there an automatic gain control time
>>constant somewhere that I didn't adjust?
>>
>>Connectix tech support couldn't help me with this one; I hope you can.
>>
>>Thanks in advance.
>>
>
>That's funny...you would think Connectix could explain this to you.
>
>Flourescent lights flicker at 60 hz. This is why you get dimmer/brighter
>pix under it. Incandescent lights are on constantly. This is not a problem
>with your camera. The camera is taking frames every x miliseconds and
>sometimes it happens to take a frame when the flourescent bulb is off.
>
>Bill Woodland (wcw@bga.com)
>Squeek on Undernet IRC
>Channel Manager #CU-SeeMe
>PC only, no MAC questions, please.
>http://www.realtime.com/~wcw/
>
>
>
>
>
Chuck Elliot
Sheffield Hallam University UK
tel. 0114 2533135: fax. 0114 2533161
email C.Elliot@shu.ac.uk
www http://kingfisher.cms.shu.ac.uk/chuck.html