On 9/18/12 6:54 AM, Bob Camp wrote:
Hi
The shutter on a conventional movie projector is very much an on / off
device. They run well below 120Hz.
Actually, the typical movie projector uses a rotary shutter which runs
at twice the frame rate (e.g. 48 flashes/second) and is hardly a fast
transition.
The actual waveform is more like a trapezoid (imagine a narrow beam of
light going through a rotating disk with two sectors in it..)
There's also noticeable movement of the film as the shutter is opening
and closing, however, your eye/brain is pretty immune to overall image
shifts, particularly when it fills the field of view: it's not much
different than handling the saccades of your normal eye movements.
24 fps is quite visible to most people (hence interlace on TVs to get 50
or 60 fields/second)
The phosphors in a white LED are at least
as long persistence as those in a TV set. There are a *lot* of TV's out
there that refresh at 60 Hz or less.
Bob
-----Original Message-----
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of Poul-Henning Kamp
Sent: Tuesday, September 18, 2012 9:05 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Hi Power LED Light power supply...
In message <ac9e4c92327746d4a521facd35d9d...@vectron.com>, "Bob Camp"
writes:
I suspect those same 120Hz sensitive people would not be able to watch TV
or
a movie :)....
I suggest you either carry out a couple of experiments yourself, or
go a little easy on the irony.
CRTs, and LCDs go out of their way to avoid flickering using physical
or electronic persistence, whereas a naked LED wil happily flash
up to several hundred kHz if you ask it to.
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