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Old 01-22-2018, 03:42 PM
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How a TV Works in Slow Motion

A fascinating video from one of my favorite channels on Youtube, the Slow Mo Guys. We all understand the concept of building an image on a CRT screen by scanning the electron beam left to right and top to bottom, but in this video they use an ultra high speed camera to see the process as it occurs. At 380,000 fps, the individual scan lines can be seen as they are drawn left to right. They also look at LCD and OLED displays in the video so you can see how these technologies differ. The CRT part is approximately 1:44 - 4:05.

https://www.youtube.com/watch?v=3BJU2drrtCM


Last edited by SpaceAge; 01-22-2018 at 11:41 PM.
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Old 01-22-2018, 08:17 PM
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I saw that the other day and almost posted it myself.
I do not think I have ever seen an actual depiction of the beam scanning the face of the tube. Just representations.
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Old 01-22-2018, 10:45 PM
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Yeah! A friend showed me this yesterday, damn cool vid.
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Old 01-23-2018, 09:37 AM
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Nice video. I was surprised to see how short the phosphor persistence actually is, fading out after 2-3 scan lines. MUCH shorter than I thought compared to the visual persistence of the viewer's eyes.
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Old 01-23-2018, 11:14 AM
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Quote:
Originally Posted by N2IXK View Post
Nice video. I was surprised to see how short the phosphor persistence actually is, fading out after 2-3 scan lines. MUCH shorter than I thought compared to the visual persistence of the viewer's eyes.
Most of the glow is gone within a few microseconds. However, the glow has such a long tail-off (even slower than exponential in most cases) that this short decay is necessary to prevent visible trails following bright objects. Some CRTs did not meet this criterion, and you could see white trails following scrolling white titles on a black background. The first large screen high definition displays available to researchers were Hitachi rear projos, which had notoriously slow decay of the long tail.

Rough calculation: Suppose half the light is gone in one microsecond. This means that during that microsecond the spot is approximately 17 THOUSAND times brighter than the average brightness of the picture (which lasts 1/30 of
second); so, due to the dynamic range of the eye, the afterglow needs to be only about 1/100 of the average to be visible, or about one two-millionth of the peak.
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Old 01-23-2018, 06:30 PM
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I imagined something like that but didn't think of the short persistence.

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