I was reading an article on the new LG display with a refresh rate of 7680Hz and it says:
While a typical refresh rate for a monitor might be 60Hz-240Hz, an outdoor display designed to be viewed from a distance needs to be much higher
The idea that there’s an intrinsic link between refresh rate and viewing distance is new to me and feels unintuitive. I can understand the need for high brighteness for far view distance. I also could understand refresh rate mattering for a non-persistent (CRT) display. But for an Led display surely you can see it far away even if it refreshes once a second?
Refresh rate normally needs to be high enough to avoid pixels “jumping” between refreshes on high resolution displays, so wouldn’t higher view distances allow you to decrease the refresh rate?
Is the article just spouting bullshit? Or is there an actual link between refresh rate and view distance?
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With refresh rates like that, you must be talking about LED billboards.
These are different from consumer monitors, which mostly use constant LED backlights and a liquid crystal layer to determine color.
An LED bilboard is going to have a fuckton of singular LEDs - each of which can emit exactly one color - arranged in groups to form full pixels capable of displaying many colors. There is no extra LCD layer between your eyes and the billboard LEDs.
The reason for the high refresh rates is because each led must be extinguished and and relit to redraw the image, and the eye is very good at picking up this strobe effect.
The difference vs. a consumer display is that the backlight in a typical monitor is constant. Refreshes the screen involves sending updated instructions to the LCD layer, twisting the crystals and possibly changing the color they allow through.
To make a crude concrete example:
Imagine I am shining a white flashlight in your face. In front of the flashlight I put a colored piece of plastic so the light hitting you is colored. Then I change the plastic to one with a (slightly) different color. I do this 120 times per second. That is a typical consumer display.
Now imagine I am shining a colored flashlight directly in your face. Then I turn it off and grab a flashlight of a different color and shine it in your face. Imagine I do that 120 times per second. That is an LED billboard.
Which do you think is more likely to give you a headache?
One final complication - the brightness of the LEDs is variable over time, they received a modulated signal rather than a steady voltage, so at lower refresh rates there will be a noticeable ripple across the image, similar to how early CRT screens could look.
Increasing the refresh rate hides a lot of these problems.
This is really interesting. I work in a casino and I’d say 90% of slot machines are now just video based.
I’ve noticed when looking a far distance across the gaming floor, slot machines that are physically far away from me appear to have “choppy” reel movement when they spin. As I get closer, they smooth out. It’s really jarring at first and it made me think of video games where things in the far distance are rendered with low resolution models that are replaced with higher resolution models as you get closer.
Maybe there is something to how we view refresh rates from distance that our eyes just lose frames or something.
Maybe so it won’t flicker when filmed?
Isn’t that more about the specific number than it just being a high number? Like it needs to be a multiple of the refresh rate of the video recorder.
In theory yes, but as there are many different video recorders, going with a super high refresh rate could be a better catch-all so to speak.
My guess is there’s been a game of telephone with the information.
The refresh rate likely refers to the drivers of the individual LEDS making up the panel.
For those confused, getting a nice linear output from an LED is extremely difficult. They vary significantly based on age, use, and manufacturing tolerances. It’s far easier to just set a max output, and use PWM. By combining 3 (or more) LEDs in a cluster, you can make the full mix of colours and brightnesses available.
Most generic led drivers work at a few khz, so 7.68khz is noticeably higher than normal. This is particularly important at low brightness. If your operation in the bottom 1% already, your available brightness levels go from 20 to 768. This would be particularly important with an outdoor screen. In daylight, you need a lot of output. The same output at night, however, would be blinding.
For an alternative comparison. An HD 50p video signal is 3Gbps. At 7680Hz it would be 460Gbps, an extreme ask of any sort of network. For no significant gain.
