Hey...hey, that's a bit too on-topic, don't you think?

Doppler Effect is light as well, that's why it pertains to the red shift of the expanding Universe.

But even if you could detect such a shift in a rotating wheel, presumably it would only affect the color of the bits moving toward you and away. But since you don't see a red shift in the color of a train or jet as it races by & away, this can't be applicable. Though theoretically, I would think there must be some infinitesimally small amount of physical red shifting. There, back off-topic. I knew I could do it.

RBG

I just finished rereading this thread. Kucharek (humming) and extravoice (chattering teeth) illuminated the heart of the matter in re apparent motion of wheels in daylight. When driving down the road in traffic, every little bump moves your eye in random direction. Each little jiggle moves the image to a different place on the retina. Our brain interprets those discrete images as stills and sees them as a strobe effect! you can get a similar still image effect by flicking your vision to and away from the wheel.

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T. Anderson

I'm going to suggest to you that these annoying Christmas lights are made to flicker. Because I don't really think driving an LED without flicker is a difficult task to accomplish. I don't have a lot of experience with Christmas lights though, I'll admit.

I think it's much higher than that on a CCFL. Do you think you can detect this flicker? It has absolutely nothing to do with the refresh rate or the frame rate anyway...

If the frequency of the backlight was 24 Hz, yes, that would probably drive you nuts. But to do that something would have to be broken, and that's not the refresh rate anyway. The refresh rate could be 24 Hz, and it would look splendid with 24 FPS material.

Well, for the backlight, they have to deal with the nature of AC the same way every fluorescent light you come across does. And they do this independent of the refresh rate.

Your ability to find that one sentence and ignore everything else is unique. You really only had to go one sentence further: "Simple potentiometer adjustments can be made to minimize the effect since LCD flicker arises from an offset of the common voltage, not a refresh signal. "

So unfortunately, refreshing an LCD at 120 HZ or even 1200 Hz isn't going to help with the form of flicker being discussed in that article. But fortunately, you can't see it anyway.

I know you can get an acceptable image at 24 Hz with nothing more exotic than the technology that was common several years ago, because I've seen it. And it's better than any 60 Hz TV I've ever seen, because it doesn't have that lopsided judder. But go to an electronics store and look for yourself.

Well, yeah, 24 FPS is choppy... even if you refresh it at 120 Hz on an LCD. In fact, I would say it is precisely as choppy at 120 Hz as 24 Hz. There is no, none, nada, zero difference.

EricM407:

LED lights that flicker 60 times a second are not doing it for effect. Most people can't perceive 60 cycles. But google "LED Christmas light flicker 60 Hz" and you'll find a sample of at least a hundred folks it drives bananas.

Florescent lighting used to similarly really irritate me. "Older fluorescent fittings using a magnetic mains frequency ballast do not give out a steady light; instead, they flicker (fluctuate in intensity) at twice the supply frequency. While this is not easily discernible by the human eye..."
http://en.wikipedia.org/wiki/Fluorescent_lamp

"LCD flat panels do not seem to flicker at all as the backlight of the screen operates at a very high frequency of nearly 200 Hz"
http://en.wikipedia.org/wiki/Flicker_fusion_threshold

I can actually see the high flicker on my own modern HPw2207 LCD as I write this. It's hard to believe this light could be running at 200 Hz. But that is precisely why they needed run them so high. It's related to human Flicker Fusion Threshold, the reason movie projectors, TVs & CRTs had to artificially introduce higher flicker frequencies.

My point re LCD flicker, of course, is that... LCDs flicker. (From more than one source as you acknowledge)... not whether it is related to a refresh signal. In fact my whole premise is that an LCD image has its own flicker problems that must be addressed; similarly film projection, television and CRTs. In each case, the solution involves provision of an acceptable flicker rate.

This thread started with the point that somehow LCDs were immune from flicker. That there was "no light cycling" involved with LCDs. Well of course there is. And your 24fps LCD "acceptable image" is only acceptable because the technology deals with LCD flicker.

That aside, agreed, most computer rendered video at 24 fps with an ultra-high refresh would look just as choppy. You need to up the frame rate itself for an improvement there.

"It is argued that games with extremely high frame rates "feel" better and smoother than those that are just getting by (referred to as "buttery smooth" by devoted gamers)."
http://en.wikipedia.org/wiki/Frame_rate

As I mentioned above, I would describe Doug Trumbull's 60fps Showscan as "buttery smooth" as well.

RBG

Kaptain K:

I too have the "power" to momentarily freeze the rotation of certain objects (ie: fan blades) with the flick of an eye. So I'm almost ready to accept your explanation. The problem remains that those eye flicks whether purposeful or through car bumps, etc. would only produce one freeze frame, so to speak. And to get a rotating object to appear to reverse itself would require a whole long series of precisely timed eyeball-produced freeze frames. I read somewhere (above?) one interesting solution that builds on your idea and that is that some people can cause their eyeballs to vibrate (purposely or unconsciously I presume). The interference between the two frequencies could be responsible for the phenomenon.

But even after all the above, until I see & study the effect again, I have to admit to some creeping skepticism - whether I have ever seen it happen without any of the usual explanations.

RBG

An out of balance wheel, slightly warped brake disk, flat spotted tire or worn CV joint could cause a slight vibration that even when unnoticed could be enough to cause a wheel to appear to slow, stop or reverse.

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T. Anderson

Actually, that wasn't your point at all. Your point was this: "a high screen refresh rate will at least rid the viewer of the irritating strobe effect that can often be seen in bright NTSC sources and, for me, all PAL sources."

Which was wrong with respect to LCDs (or any other modern digital display). And since then you've spammed me with a bunch of increasingly irrelevant links that I don't think you're even bothering to read. I'm going to do what I should have done about five posts back.

I've made a clear case, citing references, for the need and mechanism for ridding the viewer of irritating strobe effects first with film, then TV, and then LCD panels when you brought it up. That should have been enough.

RBG

This seems to be a recurring question. It's been discussed before, here and here.

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That was great, actually. Especially the second one. Thanks.

RBG