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Can anyone explain in detail the difference between Refresh rate and Flicker rate in a CRT ?

  • I won't answer because it may be a term of art, but whenever I see "flicker rate" used (and I just did a quick book search on the phrase as well), it appears to refer to refresh rate. Even in technical papers. – horatio Oct 29 '13 at 17:00
  • I've never even heard of flicker rate, so my guess is that @horatio is correct. – AJ Henderson Oct 29 '13 at 19:48
  • Guessing? I take it you both never had the pleasure of quality control testing for medical film recorders. – filzilla Oct 29 '13 at 20:04
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In the context of a CRT vs. flat panel, that is a Cathode Ray (vacuum) Tube, you have to consider the following:

1) Video sync as broken down to Vertical and Horizontal scan rates.

2) Phosphor persistence (the length of time the phosphor coating on the inside of the CRT will glow). "Phosphors are available with persistences ranging from less than one microsecond to several seconds."

http://en.wikipedia.org/wiki/Cathode_ray_tube

These two factors will determine the overall picture quality with regard to time.

Refresh rate would be best explained as vertical frames per second, for NTSC it is 60 fps.

Flicker rate includes the refresh rate plus factoring in the persistence of the phosphor.

Long persistent phosphors were employed in radar screens and O'Scopes as to allow objects to last longer on the screen while shorter persistent phosphors were employed in most consumer TVs to reduce motion blur.

"Flicker occurs on CRTs when they are driven at a low refresh rate, allowing the brightness to drop for time intervals sufficiently long to be noticed by a human eye..."

http://en.wikipedia.org/wiki/Flicker_(screen)

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    I don't believe you are incorrect, but I note that "Flicker Rate" is not a phrase that occurs in the Wikipedia article you linked. Obviously flicker is a function of time as you described, but do you have anything which contains the (jargon phrase) flicker rate? i.e. is this a "term of art"? – horatio Oct 30 '13 at 15:34
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    This behavior could be described using a function of time, such as Flicker Rate = Frame Rate / Persistence of Phosphor. So not art, maybe jargon, but certainly physical fact aka science. – filzilla Oct 30 '13 at 18:30
  • In the wiki link, there is a footnoted paper: persistence affects required brightness, not refresh. In that paper, the closest I could find to a term that resembled the OP's question was "flicker threshold frequency" – horatio Oct 30 '13 at 18:43
  • Good find ! however refresh rate will affect how much flicker one perceives so refresh rate and flicker are related so more science to boot. Thank you. – filzilla Oct 30 '13 at 19:39
  • Horatio, another example would be the pulse rate of a fluorescent light which also uses a phosphor coating. If the phosphor persistence is significantly less than the energizing pulse you would see flicker, or if you took a high speed motion image capture of the average fluorescent light, and then slowed it down you could see the Delta brightness aka flicker. – filzilla Oct 30 '13 at 19:46
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Refresh rate is the frequency at which an image in a moving picture system is redrawn on screen. In modern video systems, for instance, the screen is redrawn 59.97 times per second. The refresh rate is 59.97. Motion picture projections flash a new image at 48 times per second. Film projectors flash each frame of film twice, which is how you get from 24 frames per second to a 48 image per second refresh rate.

Flicker rate refers to how rapidly images must be presented to in order that a human viewer does not perceive a "flicker" between images. It is a threshold number. Presentations above the "flicker rate" appear continuous while those below the flicker rate appear to flicker on and off.

The actual flicker rate varies with circumstances but the "flicker rate" is historically agreed to be 48 presentations per second, plus or minus. This is why projectors flash each frame twice, turning the 24 frames per second into 48 flashes per second to hide the flicker, and why old films, shot at 16-18fps flicker noticeably on screen.

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