I don't think that's true, but I don't want to derail the thread further, so I'll move this to your wall :)

like I said it depends on how good the vision of the person has, I assume the 17'4" is for imperfect 20/20 vision for 20/12 vision (common for teenagers)  yuou need to be ~29 feet away

I had to look up what 20/20 vision means to make the conversion. If I understand it correctly 20/20 vision corresponds to being able to read text where the black lines are seperated by 1 arc minute, which would indeed corresprond to 30 cycles per degree. (60 alternating black and white lines) So 100 cpd corresponds to 20/6 vision. Or instead of being able to read the Snellen chart from the standard 20 ft away, you would be reading the bottom line from 66.6 ft away.

I do not assume anyone can read the bottom line of the Snellen chart from 66.6 ft away. That's not how the upper limit of 100 cpd was determined. That was done by asking people to guess which pictures looks more 'real' by showing 2 pictures at different resolution next to each other. At around 100 cpd it became pure guesswork. Unfortunately it did not specifiy what the visual acuity was of the test group.

With the iPad 4 at 13" away from you, you should be able to read the smallest bitmap font if you have 20/20 vision. Someone with 20/12 vision should be able to read that from 21" away.

For a 40" 1080p tv, at 5ft2" you should be able to read the smallest bitmap font with 20/20 vision, 8ft8" for 20/12 vision. Maybe someone with 20/12 vision indeed needs to go all the way up to 166cpd at 29ft away to get an image completely free of aliasing effects. My eyes definitely aren't that good :)

I was refering to the flicker of the flourecent tubes that was lighting the screen behind the LCDs.  I figured I was seeing that flicker - it does flicker very rapidly right?

The backlight in LCD tv's don't flicker, but the lcd panel can. It depends on the quality and how well calibrated it is.
This is a very technical explanation http://www.intersil.com/content/dam/Intersil/documents/an12/an1208.pdf

LCD monitors do have flicker if brighness is controlled by pulse width modulation. Instead of the backlight dimming, it is rapidly turned on/off to darken the screen. http://www.tftcentral.co.uk/articles/pulse_width_modulation.htm (Darwin award for who came up with that brilliant suggestion)

My 1080p 52" lcd tv has a different problem, horizontal striping. Slightly different bands of brightness going accross the screen. It's not noticeable in normal viewing but when you get smooth gradients it becomes visible. It kinda destroys the easthetic of the darker levels in Journey. The tv is from 2006, so maybe it's age related, the thing is on all the time.


I looked into it a bit further and apparently most new lcd tv's use PWM now :(
I can't find a definite answer about OLED, plenty of complaints of flicker there too though, but no straight answers why.
The only true flicker free option seems to be an LCD projector with a constantly lit bulb (using a mechanical iris for dimming). There's still the possibility of the lcd panel causing flicker. (And expensive bulbs that degrade over time, nothing is perfect)

All fluorescent lights flicker.  Some more perceptibly than others. I was talking about the flicker of the backlight.  Just the backlight on by itself with no picture.  It fast, but it's flickering.

LED’s flicker too.  Some not even as quickly as a fluorescent light and it baffles me it doesn’t annoy other people.  At holiday time, some people but up those flickering lights and it keeps me out of certain places.   And the LED that is on cars and the front of the Xbox really annoy me with their flicking.

But it is fast enough I don’t notice. But it does have to be rather quick.

What is wrong with PWM?

LED tv's and lcd monitors turn the LED's quickly on and off for brightness control with Pulse Width Modulation, introducing flicker.
LED christmas lights are bad, the cheap ones flicker at 60hz, recitified or 'flicker-free' ones still flicker at 120hz. LED lights on a dimmer flicker more as brightness is adjusted by the on/off cycle of current.

Good non PWM CCFL LCD backlights flicker above 5,000hz (unlike the old fluorescent tubes that flicker at 50/60 or 100/120hz).
Yeah it flickers but nothing compared to PWM LED and CCFL lit displays that flicker between 175hz and 220hz.
(PWM controlled CCFL backlights are still superior to LED backlights in regards to flicker as LED turns dark much faster, better response time but also more noticeable flicker)

Projector lamp bulbs don't have any mechanical flickering, however as the bulb ages it can flicker for periods of time as individual filaments inside the bulb start to fail with age. The first 500 hours are golden, bit expensive to replace it every 500 hours though...

I hate those strobing LED lights too, very annoying to look at. LCD data projectors are bad too, I keep getting weird flashes while using them. LCD tv's still good to me, but I find 120hz plasma tv's annoying to look at in stores. I hope OLED will be a good alternative but so far I've only read about a lot of problems with them.