30

In the CRT era, refresh rates ranged from 50 to 160 Hz. Some displays could barely do 65, high-end Mitsubishi and Sony tubes could run 120+; most people used 70-100 Hz. GPU DACs and monitor circuits were hard to scale past ~180 MHz pixel clock, forcing refresh rate vs resolution tradeoffs.

Then, in the mid-late 1990s, as LCD monitors hit the desktop market, they all went 60 Hz, even though power frequency no longer mattered. Some early low-tech ones were 30 Hz, and a 75 Hz option persisted, but wasn't even marketed as faster. LCD panels had very different speeds - color-accurate IPS could have response as slow as 50-70 ms, while TN and fast VA with overdrive hit 10 ms. Yet it took a decade till the first 120 Hz LCDs, and they stayed rare. And nothing at all between 75 and 120.

I imagine the choice of 60 Hz had to do with US TV standards, but not all panels were dual-purpose. 5:4 has never been a TV standard, neither has 16:10, these were only ever made for PC monitors. The circuitry had to support VGA, BNC or DVI, markedly different from composite or S-Video, so it also had little commonality with TVs. For the secondary option of 75 Hz, no idea. And there's been nothing at all between 76 and 119 Hz.

Even TVs weren't all fixed at 60 Hz - they had 50, 60, 100 and 120 Hz refresh rates (even if they couldn't take input above 60 except as 3D-stereo). Game consoles varied by market, whatever local TVs used. While 60 Hz was good enough for most, it's been more common for PCs to offer a range of options from bare-bones to extravagant, as they did with CRTs, and as they do today.

Was there any reason for the ubiquity of 60 Hz refresh, beside being "good enough"? Agreements, standards, or maybe a specific component that display or GPU makers couldn't easily buy or custom-build to support other refresh rates?

1

3 Answers 3

28

To be fair, cost, need, and usefulness of anything above the standardized 60 Hz minimum for different resolutions are the reasons why it took long for LCD monitors to go past 60 Hz.

The LCD panels were slow, compare that to a CRT with long decay phosphors. The settling time of new pixel value was long. But the image still needs refreshing at some rate or it starts to fade. The panels were meant for 60 Hz in every aspect, so they would not work at 30 Hz refresh rate. Also no computer had any standard formats that could go much below 60 Hz and there was no data structure in the monitor EDID that it could advertise support for formats below 60 Hz. So the best option is to make an LCD to look like a 60 Hz CRT as that is all that is needed for it to work without reinventing the whole ecosystem from the ground up.

If 60 Hz is enough so that the screen does not look like it is flickering, why go beyond 60 Hz? People may have used CRTs at higher than 60 Hz if it looks like it flickers at 60 Hz. Which is why even on a legacy IBM VGA, all the resolutions were 70 Hz except for the highest 640x480 which was 60 Hz, so in fact, if you ever used an LCD in DOS, it had to support a couple of 70 Hz formats anyway, I had a LCD which had a menu to select between 720 and 640 pixel modes depending on if you used it for text or graphics.

Also if you use higher rates, the display has to have a more expensive triple video ADC to sample at higher pixel clock. The display panel must also support the higher pixel clock rate on the digital bus.

Also all formats that are not the native panel resolution needs to go through a scaler chip, so again all the data that goes into and out of the scaler must have a sensible data bandwidth limit as it must always output the native panel resolution.

And again, if the pixels are slow anyway and can't change colour quickly enough to be useful beyond 60 Hz, using higher rate than standard minimum of 60 Hz for any resolution will just go to waste.

Only later when technology matured and there was a market for faster displays, they became available. Panels became faster, the analog monitor interfaces were replaced with faster digital interfaces, and other technology such as the interface and scaler chipsets got cheaper, and there was a market (gaming) which benefited from higher refresh rates, and also computers now had powerful graphics accelerators that could deliver 120 FPS content over 120 Hz resolutions.

And for the "Why 60 Hz, why not something else?" part, the general ecosystem with external displays had for a long time been using CRTs that have their history in TV screens and TVs worked at local mains frequency 50 Hz or 60 Hz, so CRT technology cheaply available for consumer products has always been around 60 Hz. During 90s when resolutions improved, and while the bandwidth can be used for higher refresh rates at lower resolutions, the CRT phosphors simply started to cause flicker if less that 60 Hz was used. So for most video cards and monitors, they used standardized formats and the highest supported resolution was only reaching the 60 Hz minimum required for usable operation. Standard video card drivers rarely allowed non-standard refresh rates below 60 Hz, and depending on the hardware, it might not be even possible to select custom pixel clocks or horizontal rates or lines per frame to support lower frame rates. And the highest possible refresh rate at some resolution is set by the pixel clock which can't exceed the limit of the chipset.

Even the EDID standard for PNP displays allows defining supported Established Timings starting from 60 Hz, the Standard Timing flags already being de-facto formats at 60 Hz or above. Custom format support could be defined by picking any within range of indicated Monitor Range Limits descriptor, or the monitor could say one or up to four Detailed Timing Descriptors but it does not mean that all video sources can configure itself to any requested timing format.

1
8

One benefit of high refresh rates on CRTs is to re-energize each phosphor more frequently, so decay between scans is less. And any pulsing of brightness happens at a frequency well above human persistence-of-vision.

(Correction, apparently I was wrong about LCD pixels holding their state on their own; they do need refreshing, so this part of the answer is at least partially wrong.)

This benefit doesn't exist on LCDs which are naturally flicker-free. Each pixel stays at constant brightness for longer, maybe? LCDs work by filtering the backlight, and each pixel can hold its "setting" much(?) longer than the phosphors on a CRT. Changes happen actively, not just by waiting for a phosphor to decay. (Which requires the decay time to be short enough to not smear images.)

Although early LCDs were not fast, especially low-power ones like used in laptops, so high-motion would turn into a smear, but static images and text were fine. That's another reason it wasn't very helpful to have higher refresh rates: if the frame interval is shorter than the settling time for a pixel to change to a new colour, you don't get the full benefit. Different pixels can be in different stages of shifting to a new colour if they started in different frames, and there can be benefits for V-sync and stuff like that. (The early LCD era was over a decade away from adaptive sync (freesync and g-sync) where the monitor can accept a new frame whenever the next one is ready within some min/max interval, instead of at a fixed cadence.)

With the early panels themselves not able to shift colours quickly (but not having any flicker regardless of refresh rate), there was little incentive to accept higher refresh rates from computers. So I assume cost was a major reason manufacturers mostly didn't use more expensive parts capable of operating at higher frequencies in most panels.

With early LCD panels not being good at high-motion regardless of refresh rate, most people who wanted that would simply use CRTs. So a high-refresh-rate LCD probably wouldn't sell well, since it couldn't fully compete with CRTs for use-cases where that mattered. (Unless I'm mistaken and there were some fast panels even back then which could have been used in gaming LCDs.)

8
  • 3
    "Each pixel stays at truly constant brightness regardless of refresh rate" is an overstatement. Try driving an LVDS TFT panel intended for 60 Hz nominal operation forcibly at 24 Hz and see the flicker. The image does start to fade away immediately after it has been refreshed but so slowly that it can't be detected when refreshed at 60 Hz. But it is definitely not constant.
    – Justme
    Commented Aug 29, 2023 at 22:39
  • @Justme: I see, thanks for the correction. Is it still a (much?) slower fade than CRT phosphors, or is my answer based on a false premise? Commented Aug 29, 2023 at 23:55
  • @Justme so this could be a good reason that 60Hz was choosen as the standard refresh rate...
    – UncleBod
    Commented Aug 30, 2023 at 7:04
  • I had few old LCDs that flickered the worst was some lenovo 15" (maybe 15-20 years ago) it had some weird post processing that caused huge response times and flickering (similar to CRT) that was on by default ... after turning it off it was much better but still way too slow (I had mabe 8 years older noname LCD that was simply perfect and fast was still in use last year but the LCD started to leak :) )... older B&W LCDs from old (286/386) laptops I used for MCUs aplications also flickered just like CRT...
    – Spektre
    Commented Aug 30, 2023 at 7:24
  • 1
    @PeterCordes the old B&W even on static (performing black blank frame similar to CRT confirmed with 240fps camera I was very supprised that old LCD flat panels did that too at that time) and the "newer" in some cases also on static images but not always depending on OSD menu settings tweaks and image brightness... however I had many other LCDs (older and newer) that where fine without any flickering too
    – Spektre
    Commented Aug 30, 2023 at 12:40
7

I would say that 1990s LCD displays did not use 60 Hz refresh. At least the one I had on my first laptop in 1997 was a passive matrix display, with 30 Hz refresh rate and very slow response time. Not very good for gaming or watching videos on. Faster LCDs with active matrix TFT technology started to become affordable in early 2000s.

For the later displays, 60 Hz is a balance where tearing and unsynchronized refresh rate issues are tolerable.

V-sync support in PC games and operating systems was still uncommon, and adaptive sync non-existent. This caused frame time jitter and frame tearing.

For example if a game would render frames at 29 Hz and display would independently update at 30 Hz, the actual display period would alternate between 33 ms and 67 ms. With same render rate and 60 Hz display, the alternation would be between 33 ms and 50 ms, a much less noticeable jitter. Any frame tearing would be visible half as long.

Game consoles generally had working V-sync support, and because the hardware was standardized, designing games to match the display rate was easier. This allowed them to get reasonably smooth motion with 30 Hz refresh rate.

5
  • 2
    An LCD integrated to a laptop is wildly different from an LCD monitor that has to work with existing video interface. Even consumer LCD TVs had no way of supporting 30 Hz over extetnal interfaces before 2002 when the standard indicating such formats became available, and it took years to be able to buy an affordable TV with support for 30 or 24 Hz frame rates, mainly used for movies or console gaming.
    – Justme
    Commented Aug 29, 2023 at 10:11
  • TVs are a special case, but VGA (and later DVI) is perfectly capable of supporting refresh rates lower than 60 Hz.
    – jpa
    Commented Aug 29, 2023 at 10:22
  • 3
    They are capable as interfaces for anything but the devices on either end of the cable may not be, due to hardware, software, or there not being a standard for presenting that info. DVI for example requires that you only send formats that the monitor says it supports in the EDID, but the list of possible formats has no formats with less than 60 Hz refresh rates so you can't really advertize them even if you did support them. Same for VGA. Only format less than 60 Hz is 800x600 at 56 Hz.
    – Justme
    Commented Aug 29, 2023 at 10:54
  • Hmm, that's interesting information and could be partial answer to the original question (and I see you added it to your answer :). I have used 50 Hz refresh rates to get higher resolution, but that required manual override on operating system side.
    – jpa
    Commented Aug 29, 2023 at 10:56
  • 2
    @Justme - my first interaction with an LCD display was in late 1993. It was basically an early laptop display turned into a stand alone monitor. The case for laptop LCDs was clear at the time - better battery life. But CRTs were the gold standard for normal displays. Well, except when the display had to be near a giant magnet for an ECR plasma chamber that made a CRT totally unusable. I have no recollection of what the refresh rate of that display was, but it didn't matter - it was better than no display.
    – Jon Custer
    Commented Aug 29, 2023 at 15:30

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .