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How a TV Works in Slow Motion - The Slow Mo Guys

The Slow Mo Guys2 HN recommenders · recommended in 2 months, 2022–2026
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explainer · general · evergreen · 2022–2026 on HN

The Slow Mo Guys film a TV and screens with a high-speed camera to show how displays build an image. The footage includes CRT-style scanning and how pixels light up over time.

Frequently linked as visual proof of how a CRT's raster scan and phosphor decay work.

8 comments from Hacker News

@kevincox2026-03 · in “JPEG Compression”

That's not quite true. Only one pixel is being activated at a time but the phosphors continue to emit light for many pixels. In practice you get a handful of lines lit to varying degrees at at time. Maybe 1-2 lines quite brightly lit and then a trail of lines that are fading pretty significantly (but still emitting light). They yes, our persistence of vision fills in the rest to provide the appearance of a fully lit screen. This video has some great slow-mo of CRTs ▶ this video

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@retrac2025-07 · in “How does a screen work?”

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: ▶ this video

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@rcxdude2025-01 · in “Blur Busters Open Source Display Initiative – Refresh Cycle Shaders”

They frequently flicker or are only showing part of an image in video footage or photos, for exactly this reason. They're a right headache to film clearly. (see this youtube video showing one in slow-motion to get an idea: ▶ this video )

@chongli2023-12 · in “Checkmate 19" IPS Retro Monitor”

That's an oversimplification of the physics. CRT televisions have very low persistence phosphors. If you look at high-speed video of a CRT during a raster scan, the line is visible for far less time than the entire frame [1]. This technique relies on persistence of vision [2] to create the illusion of a complete frame. If you want to calculate the response time of a single dot on the phosphor, it is way down into the microseconds. I don't know enough about OLED displays to comment. I do know that LCDs don't even come close to the speed of CRTs at transitioning through high contrast images, the key to producing fast and responsive motion of sprites (which are high contrast against the background by design in most retro games). [1] ▶ this video [2] link

@mortehu2023-11 · in “Simple streetlight hack could protect astronomy from urban light pollution”

If you look at high speed footage of a CRT monitor, you'll see that only a few scan lines are lit at a time. ▶ this video