How a TV Works in Slow Motion - The Slow Mo Guys
Why Hacker News recommends it
Frequently linked as visual proof of how a CRT's raster scan and phosphor decay work.
What it is
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.
Recommended by 2 HN commenters across 2 different months, 2022 to 2026.
What Hacker News said
Recommends retrac · 2025-07 · on “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]
Recommends kevincox · 2026-03 · on “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]
Cites rasz · 2022-06 · on “Video codecs and 4k”
1. As GL1zdA already pointed out in blog comments 1992 Creative Video Blaster CT6000 was a single frame screen grabber and not a video encoding/decoding accelerator. YT "Creative Videoblaster CT6000 in action" [LINK] shows what it does. [LINK] "converts a standard full-motion video image (composite video source) into a format for display on a computer graphics monitor" emphasis on the _image_. "It can position and scale the video image onto the output display and allows the video image to be merged with computer graphics for interactive multimedia applicaiton." means overlay analog video on VGA monitor. The first true video decoding accelerator on PC market came out of David Sarnoff Research
Cites iforgotpassword · 2023-03 · on “Secret Colours of the Commodore 64”
It's said later in the article that you'd need two colors with similar brightness to avoid perceivable flicker. CRTs did have some afterglow but it wasn't even for a full frame, let alone two. [this video]
Cites aimor · 2023-10 · on “How Games Used to Look: Why Retro Gaming on a CRT Looks Different [video]”
"The video makes it seems that there's no temporal bleeding on CRTs. This sounds unlikely to me..." There is, but I don't remember it being noticeable even on cheap TVs. I still miss the lack of motion blur that CRTs gave by default. I found a forum post where someone lists these values: "Phosphors in current use for CRT-applications: Red: phosphor = Y2O2S:Eu3+. Lifetime (1/e time) = 150 us, single exponential. Green: phosphor = Zn2SiO4:Mn2+. Lifetime (1/e time) = 10-15 ms. Clearly, this is quite long and is the limiting factor in increasing frame-frequency. Note: the emission decay has a highly non-single-exponential decay --> at long times (~1 s) still some emission can be observed by the
Cites mortehu · 2023-11 · on “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]
Cites chongli · 2023-12 · on “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 backgro
Cites rcxdude · 2025-01 · on “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] )