Hello, I am a newbie here and I don't know what this thing is, er..

Oops, wrong server.

Reallyy, what *is* persistence of vision? I know it's some phenomenon
but I don't know what it is (or, more likely I know, but can't match
the name with the thing). I know you guys, 80% of the replies will be
of the nifty smartass type :) but still...


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] usanet
TAG      e-mail : pet### [at] tagpovrayorg

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Peter Popov wrote:
> 
> Hello, I am a newbie here and I don't know what this thing is, er..
> 
> Oops, wrong server.
> 
> Reallyy, what *is* persistence of vision? I know it's some phenomenon
> but I don't know what it is (or, more likely I know, but can't match
> the name with the thing). I know you guys, 80% of the replies will be
> of the nifty smartass type :) but still...

Not really the best question for this group but...

Let us use an example to describe the persistence of vision effect.
As you know it is possible to blink a light bulb or an LED and see
the individual flashes. As we speed up the flash rate it starts
to appear as though it is constantly lit even though we can verify
for ourselves that we are indeed still pulsing the light. This is
known as the persistence of vision effect. It is the same reason
why light bulbs that run on alternating current appear constantly
lit when we know that they are actually turned off and on 60 times
per second. The reason the light appears persistent is because
the light receptors in our eyes cannot react quickly enough to
resolve the individual on off cycles. There are other examples
of the persistence of vision effect but this is the best way
I know of to explain it.


-- 
Ken Tyler - 1400+ POV-Ray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

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> Not really the best question for this group but...

The povray.animations group would technically be o.k. though
because persistance of vision is the reason motion pictures
work...

-- 
Phil
...coffee?...yes please! extra sugar,extra cream...Thank you.

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Ken wrote:
..
> lit when we know that they are actually turned off and on 60 times
> per second. The reason the light appears persistent is because
..

Actually it's 120 times per second.. Ok I'll go away :)

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On Mon, 08 May 2000 23:48:16 -0700, Ken <tyl### [at] pacbellnet> wrote:

>Not really the best question for this group but...

Sure! I started posting it and just before sending it I noticed it was
the wrong group so I manually typed povray.gereral in the proper
header field but I probably hit the wrong button because it defaulted
to p.b.i. Happens.

<snip description>

Thanks, Ken. I know the effect you described, but I had no idea that
was what 'persistence of vision' meant.


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] usanet
TAG      e-mail : pet### [at] tagpovrayorg

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Ken wrote:

> Not really the best question for this group but...
>
> Let us use an example to describe the persistence of vision effect.
> As you know it is possible to blink a light bulb or an LED and see
> the individual flashes. As we speed up the flash rate it starts
> to appear as though it is constantly lit even though we can verify
> for ourselves that we are indeed still pulsing the light. This is
> known as the persistence of vision effect. It is the same reason
> why light bulbs that run on alternating current appear constantly
> lit when we know that they are actually turned off and on 60 times
> per second. The reason the light appears persistent is because
> the light receptors in our eyes cannot react quickly enough to
> resolve the individual on off cycles. There are other examples
> of the persistence of vision effect but this is the best way
> I know of to explain it.

Does the bulb immediately stop emitting light when the power is cut, or does
it "cool down"?
Sigmund's right, it's 120 times a second ;-)

Know what I hate? When I go into MS-DOS mode and the monitor goes to 60Hz.

--
David Fontaine     <dav### [at] faricynet>    ICQ 55354965
Please visit my website: http:/www.faricy.net/~davidf/

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David Fontaine wrote:

> Does the bulb immediately stop emitting light when the power is cut, or does
> it "cool down"?

I used the example for purely illustrative purposes. Obviously is does
take a filament time to cool down and in fact they are specifically
designed not to. But if we were to model the filament to have a perfect
heat discharge that followed the current cycle through it in the form
of a shape edged square wave the example would fit the explaination.
LED's in fact come much closer and that is why I also mentioned them
in my example. I just didn't expect you to come along and nit pick.
If you have a better example to offer I am sure Peter would be happy
to hear it.

> Sigmund's right, it's 120 times a second ;-)

Not on a 30hz system.

-- 
Ken Tyler - 1400+ POV-Ray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

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Not only does an incandescent bulb cool down, it also does a shift toward
orange-red as it cools.

David Fontaine wrote:

> Ken wrote:
> Does the bulb immediately stop emitting light when the power is cut, or does
> it "cool down"?
> Sigmund's right, it's 120 times a second ;-)
>

--
Bryan Valencia
Software Services - Making Windows Scream
http://www.209software.com
mailto:bry### [at] 209softwarecom

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On Tue, 09 May 2000 16:25:15 +0200, Sigmund Kyrre Aas
<as### [at] studntnuno> wrote:

>Actually it's 120 times per second.. Ok I'll go away :)

Actually, a common houshold lamp can't flash that quickly. The
filament won't cool off enough between the rapid pulses of current. So
this isn't purely a simple case of Persistence Of Vision, it's also
partially a case of "Persistence of Illumination" as well.

Later,
Glen Berry

( Remove the "7" from 7no### [at] ezwvcom to email me. )

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Glen Berry wrote:
> 
> Actually, a common houshold lamp can't flash that quickly. The
> filament won't cool off enough between the rapid pulses of current. So
> this isn't purely a simple case of Persistence Of Vision, it's also
> partially a case of "Persistence of Illumination" as well.

Go to the movies for a better effect ;) Actually I had a lab project with a
light sensing thing and an oscilloscope some years ago. We could easily
identify the variation of the light from a light bulb. A gas lamp produced a
very weird noise curve.

sig

(followup to off-topic)

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