[time-nuts] Hi Power LED Light power supply...

[Jim Lux]

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-bounces at febo.com [mailto:time-nuts-bounces at 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 <AC9E4C92327746D4A521FACD35D9D654 at 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.
>