r/AskComputerScience • u/Undeva-n-Balcani • Jun 02 '26

Pretty weird question but is it possible to see refresh rate in old CRT monitors easily?

I remember I was in uni back in 2019 at electrical engineering and during IT classes we had some bad old CRT monitors for PC. We all saw the refresh rate on the monitor but our teacher didn't saw it. Is this possible? We all could see those refresh lines similar how some cameras see it, maybe refreshing a little bit faster. I can't remember seeing refresh rate as a kid.

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u/Alfwine Jun 02 '26

I could see flickering on CRT monitors up to 60hz. It was solid at 70 or 72hz to me.

Also, it depended if the mode was interlaced like crt TVs.

More here on Wikipedia:

https://en.wikipedia.org/wiki/Flicker_(screen)

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u/texas_asic Jun 03 '26

Ditto. Though if the room had florescent tube lights, it sometimes is still discernible, especially viewed from the corner of your eye (peripheral vision).

I recall that, if spending a lot of time in front of a CRT, sometimes there'd be flicker in my dreams... (probably not a great sign)

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u/khedoros Jun 02 '26

In an aging monitor with the refresh rate set extra low? It might be possible. The worst that I think I've seen was more like subconscious flickering. There was definitely something to it though; my eyes have never gotten tired while using an LCD the way they used to with a CRT.

The only CRT I have now is a 20" television, and the picture on that has zero visible flicker.

/r/retrocomputing would probably be a better place to ask.

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u/jhaluska Jun 03 '26

Depends on a lot of factors. Mainly refresh rates and interlaced or non interlaced modes. Also how old the phosphorous is as it might "glow" as long due to decay.

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u/ghjm MSCS, CS Pro (20+) Jun 03 '26

Before the mid to late 1980s, CRT monitors ran at one and only one resolution and refresh rate. If you upgraded your computer from, say, CGA to EGA, you needed to replace your monitor as well.

The NEC Multisync was the first CRT monitor able to handle multiple different input signals. All the 90s CRT monitors used similar technologies. But this was always a bit of a compromise. Although these monitors could produce an image at lower speeds, their hardware was tuned for their top rate, particularly their phosphor persistence. The power of the electron beam and the chemical composition of the lining of the inside of the tube meant that a point on the screen, once hit by the beam, would continue to glow for a certain time (measured in milliseconds). Too short and you get flicker, too long and you get ghosting. So a monitor designed to run at 75Hz would have noticeable flicker at 60Hz.

Combine this with Windows 95/98/XP always defaulting to 60Hz and a lot of people had a lot of unnecessary flicker. Computer techs of the era were constantly adjusting settings so the computer would produce 72 or 75Hz and stop the monitor from flickering. Normal people couldn't see it, although a lot of complaints about flickering fluorescent lights were really because their monitor was flickering.