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How does a screen work?

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573 points chkhd | 1 comments | | HN request time: 0.334s | source
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retrac ◴[] No.44551618[source]
CRTs are still slightly magical to me. The image doesn't really exist. It's an illusion. If your eyes operated at electronic speeds, you would see a single incredibly bright dot-point drawing the raster pattern over and over. This YouTube video by "The Slow Mo Guys" shows this in action: https://youtu.be/3BJU2drrtCM?t=190
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hinterlands ◴[] No.44551773[source]
That slo-mo video is somewhat misleading, though. The phosphor glows for a good while, so there is a reasonable chunk of the image that's visible at any given time.

The problem in that video is that the exact location the beam is hitting is momentarily very bright, so they calibrated the exposure to that and everything else looks really dark.

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layer8 ◴[] No.44552411[source]
The phosphor still drops off very quickly [0][1][2], roughly within a millisecond. That’s why you would need a 1000 Hz LCD/OLED screen with really high brightness (and strobing logic) to approximate CRT motion clarity. On a traditional NTSC/PAL CRT, 1 ms is just under 16 lines, but the latest line is already much brighter than the rest. The slow-motion recording showing roughly one line at a time therefore seems accurate.

[0] https://blurbusters.com/wp-content/uploads/2018/01/crt-phosp...

[1] https://www.researchgate.net/figure/Phosphor-persistence-of-...

[2] https://www.researchgate.net/figure/Stimulus-succession-on-C...

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bgnn ◴[] No.44553180[source]
I'm not sure about this calculation though. Phosphor decays exponentially with a time constant of roughly 5ms (according to HP [1]). This means when a new frame comes at 60Hz refresh rate there is still 10-15% of the previous frame related excitation is present. This means there is considerable amount of nonlinearity, hence the performance is even worse than 10ms LCD/OLED displays.

Genuine question: why do you think CRTs are better?

[1] https://hpmemoryproject.org/an/pdf/an_115.pdf

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1. cubefox ◴[] No.44558226[source]
> Genuine question: why do you think CRTs are better?

They have many disadvantages, but an advantage is that CRTs mostly remove the "persistence blur" induced by smooth pursuit eye movements on sample-and-hold displays like LCD and OLED. Here is an explanation:

https://news.ycombinator.com/item?id=42604613