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LCD Refresh Rate?

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January 17, 2007 11:42:55 AM

Trying to pick out a new LCD monitor for my PC, I'm being told that refresh rates do not matter in LCDs and that response time is all that matters. As in a 5ms response time is all that i should be looking for and that since LCDs dont re-distribute the pixels to the screen but just keep changing their colors (Wich is what response time is for - changing the pixel's color), that the refresh rate dosent matter in LCDs.

But i notice a HUGE difference beetween 60hz and 75hz in my LCD monitor (connected by a VGA cable), so whats up?

Thnx!

More about : lcd refresh rate

January 17, 2007 12:53:56 PM

Quote:
Trying to pick out a new LCD monitor for my PC, I'm being told that refresh rates do not matter in LCDs and that response time is all that matters. As in a 5ms response time is all that i should be looking for and that since LCDs dont re-distribute the pixels to the screen but just keep changing their colors (Wich is what response time is for - changing the pixel's color), that the refresh rate dosent matter in LCDs.

But i notice a HUGE difference beetween 60hz and 75hz in my LCD monitor (connected by a VGA cable), so whats up?

Thnx!


Not refuting your claim, but I can notice no difference between 60hz and 75hz on mine... also on VGA.

Maybe others will pipe in with their perceptions....
January 17, 2007 2:45:04 PM

No, thats impossible. 75Hz feels a LOT smoother. 85Hz on the other hand does nothing.
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January 17, 2007 3:17:56 PM

I didn't know LCDs allowed 85hz.... MANY are limited to 60hz, max, at native resolution.
January 17, 2007 5:44:21 PM

Native only means "biggest". You can set it to any other resolution without losing anything. 85hz is the maximum that LCDs can do so far.
January 17, 2007 7:14:31 PM

Quote:
Native only means "biggest". You can set it to any other resolution without losing anything. 85hz is the maximum that LCDs can do so far.


Pardon? Some settings render the display untelligible. Where did you get the notion "... *any* resolution ... without losing anything"?
January 17, 2007 8:30:58 PM

Quote:
Native only means "biggest". You can set it to any other resolution without losing anything. 85hz is the maximum that LCDs can do so far.


Pardon? Some settings render the display untelligible. Where did you get the notion "... *any* resolution ... without losing anything"?

The word "untelligeble" does not exsist, so excuse me if i discard your argument.
January 17, 2007 11:03:37 PM

Quote:
Native only means "biggest". You can set it to any other resolution without losing anything. 85hz is the maximum that LCDs can do so far.


Pardon? Some settings render the display untelligible. Where did you get the notion "... *any* resolution ... without losing anything"?

The word "untelligeble" does not exsist, so excuse me if i discard your argument.

Pardon, misspelled... meant "unintelligible"... "distorted to the point of being not readable".
January 18, 2007 4:30:08 AM

Quote:
75Hz feels a LOT smoother. 85Hz on the other hand does nothing.


you are fortunate to have found an LCD that refreshes at 75hz. usually when they claim anything over 60hz it just means that higher inputs are accepted but output is still converted to 60hz. this might be whats happening at 85hz (just guessing)

i believe you on the 75hz thing . one big reason pro gamers prefer CRT over LCD (besides ghosting) is the higher refresh rate. when concentration gets down into the milliseconds, they say there is a diff between 60 and 120hz. most people (including myself) probably cant see the difference during casual viewing (which is why i think it is always debated) but i'm fairly sure its a factor during intense aiming.

otherwise, my guess is you have set vsync to 75hz and it looked better.
January 18, 2007 12:24:25 PM

Quote:
75Hz feels a LOT smoother. 85Hz on the other hand does nothing.


you are fortunate to have found an LCD that refreshes at 75hz. usually when they claim anything over 60hz it just means that higher inputs are accepted but output is still converted to 60hz. this might be whats happening at 85hz (just guessing)

i believe you on the 75hz thing . one big reason pro gamers prefer CRT over LCD (besides ghosting) is the higher refresh rate. when concentration gets down into the milliseconds, they say there is a diff between 60 and 120hz. most people (including myself) probably cant see the difference during casual viewing (which is why i think it is always debated) but i'm fairly sure its a factor during intense aiming.


otherwise, my guess is you have set vsync to 75hz and it looked better.

Oh no! Does that mean that im going to have to buy a CRT if i want anything above 60hz?? I hate CRTs; they are big and ugly.. :cry: 

Isnt there ANY LCD that can do 75hz at a resolution higher than 1280x1024?
January 18, 2007 9:26:08 PM

no such thing as refresh rate. unless someone can prove otherwise.

there is no refresh. simple.

also native, means that each pixel out put by the gfx card has its own pixel on the screen at full screen. that is the only resolution the screen can display perfectly at full screen. some screens like mine can do 1:1 pixel scaling which does produce a native image but not at full screen. it only uses the pixels it needs to.

the reason it may feel smoother may be in your mind or perhaps you have v-sync on like th other guy suggesed and the higher amount of frames helps.

regardless there is no refresh rate. one reason i will prove this almost is that their no such thing as a constant latency. if you loo at a toms review of a monitor you will notice that it is all over the shop so since how much images is related to how quickly a screen can change its colours and since their is no constant rate at which it can do this there is no such thing as a constant "refresh" rate. the maimum FPS a LCD can display varies depending on how different each frames colours are.

track, you are beginning to get noobish again, if you ever started to learn anything in the first place which i doubt.
January 18, 2007 9:28:00 PM

120Hz LCDs are coming our way in the next few months. There have been sightings of some those LCDs already.
January 19, 2007 3:56:22 AM

Quote:
no such thing as refresh rate. unless someone can prove otherwise.

there is no refresh. simple.

also native, means that each pixel out put by the gfx card has its own pixel on the screen at full screen. that is the only resolution the screen can display perfectly at full screen. some screens like mine can do 1:1 pixel scaling which does produce a native image but not at full screen. it only uses the pixels it needs to.

the reason it may feel smoother may be in your mind or perhaps you have v-sync on like th other guy suggesed and the higher amount of frames helps.

regardless there is no refresh rate. one reason i will prove this almost is that their no such thing as a constant latency. if you loo at a toms review of a monitor you will notice that it is all over the shop so since how much images is related to how quickly a screen can change its colours and since their is no constant rate at which it can do this there is no such thing as a constant "refresh" rate. the maimum FPS a LCD can display varies depending on how different each frames colours are.

track, you are beginning to get noobish again, if you ever started to learn anything in the first place which i doubt.


You are correct, on there being no such thing as constant latency... Depending on the colors being shifted it always varies. However that does not mean that refresh rate is a useless meaning, or that the refresh rate doesn't matter. In general, the higher the refresh rate, the easier it is on the eyes, and the less image tearing there will be during fast moving images. A higher refresh rate results that all pixels in general will be able to shift faster than at a lower refresh rate. I can most absolutely tell the difference from 60hz and 75hz, it is in no way an effect on the mind or a v-sync problem, in fact 60hz monitors actually strain my eyes relatively quickly. I can actually tell when a monitor is running at 60hz just by using it shortly, because it is obviously bothering my eyes. Furthermore, I also can tell the difference from 75hz and 85hz, though it is not nearly as significant. 85 is slightly smoother, but anything higher than that and it all feels the same. Remember that different people's brains and eyesights work differently, so some people may be more sensitive to a screen's refresh rate than others.
January 19, 2007 7:32:57 AM

Quote:

how much images is related to how quickly a screen can change its colours


edited original post

from wikipedia:
Quote:
In LCDs, each pixel emits light of set intensity for a full period of 20 ms (in this example), plus the time it takes for it to switch to the next state, typically 12 to 25 ms.


so refresh is partially related to response time (confusing). in any case i think LCDs can't go above 60hz. behardware tested 6 LCD monitors (among which was the vx922 current fastest LCD)....

"
Quote:
We found the following:

2 didn´t support 75 Hz and we would have a black or unstable image.

2 said that they supported 75 Hz, but when we measured the time between images we realised that they were in fact at 60 Hz.

Finally, the last two really ran at 75 Hz…partially.....In fact, it really displayed 4 images in 67 ms whether it was at 60 or 75 Hz.

If liquid crystals move faster and blurring is less noticeable, images aren´t displayed faster on the monitor....to be honest manufacturers told us that none of the current LCDs would be able to support 75 Hz. We don’t always believe them, but out of 6 monitors this was actually the case.
January 19, 2007 8:25:03 AM

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track, you are beginning to get noobish again, if you ever started to learn anything in the first place which i doubt.


Maybe you should learn some English before calling me a noob. As if you hold a candle to me at anything else :roll:
Either help, or go away cause i dont need you.

Furthurmore, 75hz DOES seem smoother, but its NOT in games. Im talking about moving my mouse across the desktop or opening up IE and typing this message.
The thing is that i have two 17" monitors - a CRT and an LCD.
They both feel EXACTLY the same at 60hz and at 75hz. Same exact smoothness of the mouse issue.
January 19, 2007 3:58:45 PM

Quote:
no such thing as refresh rate. unless someone can prove otherwise.


I think there is still a frame clock -- the pixels are not updated willy-nilly. The display updates at each period of the refresh clock according to whatever is in the buffer in the display at the time just like with a CRT. The buffer gets updated according to how fast the graphics can be processed (or at the same rate as the display's refresh rate if vsync is on).

The new Sharp Aquos D92 line that should be in customer's hands within a month has 120Hz image refresh rate.

Now, on a CRT, the ray is scanning one pixel at a time, line by line. So most of the time what you see either the "pixel" (which is a combination of red green and blue spots of the phosphor material) glowing from the spot being illuminated for a short time by the electron, or you see a pixel that is not illuminated (I don't know how fast it fades, so I don't know the amount of time it is not illumniated vs illuminated). As a result on a CRT you see the flicker. It is true on an LCD every pixel is always displaying something, and that they change only when told but never go off unless black is being intentionally displayed. That's why you guys are saying the LCD seems "smoother." Yes the pixel does not fade like a CRT for that time between scanning.

If you don't believe that there is a frame clock, consider the bus between the display and the graphics controller. The bus is not large enough to accomodate instantaneous transitions for all pixels -- you would need however many bits for color depth for every single pixel to be able to do that. So there is a clock, and between clocks all the data is translated from a bitmap (I guess) into something that makes sense for the hardware over a grid, and at the clock rate you get the toggling all at once (best case design).

what you could do, thinking about it, is process each pixel in a scan just like with a CRT, and that would maybe eliminate the need for a frame clock? But well, it's up to the designer.. So, who knows what you're getting with any particular technology? Some displays might have some kind of processing going on with an image such that the algorithm relies on multiple pixels, or even say the white balance of the entire image -- you'd definitely see a frame clock for displays like that.

I am just as confused as anyone when it comes to what you're getting with these new displays, and the marketing lingo so far isn't very revealing.
January 19, 2007 4:03:07 PM

btw an interesting take on the word "flicker" -- the fl sound in the english language is really one sound cascading into the other (ffff followed by the l). Similarly, the scanning of a CRT is from top down. The flicker is not a result of a clocked set of images being displayed periodically, but rather from the scanning. So in the future if someone asks you can say LCDs definitely have no flicker like CRTs.
January 19, 2007 5:29:19 PM

yes, but we come to the most interesting part.

refresh rates do not exist on an LCD but they do exist on gfx cards. gfx cards, due to the use of CRT's are still very much an analog device. if CRT's did not exist then they could be solely digital which would make a difference.

images are still output as if they are output to a CRT regardless of whether or not a CRT is used AFAIK. however, a higher refresh rate setting will change the gfx card not the monitor. i have said this so many tyimes it aint funny. a gfx card needs a refresh rate signal from a monitor to work. it won't unless it gets the classic signal.

latency of a pixel cannot go higher than its max.

oh and track and the others, your personal opinon means damn all against the plain facts of how the tech works. facts>opinion.

also, it could be your monitors are crap or faulty and that what you are experiencing is something i have heard described as input lag. true some people say my own monitor is the same but i have never seen any.

that could explain why it seems smoother. i don't know why but maybe because the gfx card is "refreshing" the image more often it somehow reduces the input lag and gives the apparant effect that it is somehow affecting the way the way the monitor works instead of how the comp communicates with the monitor.
January 19, 2007 5:44:56 PM

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images are still output as if they are output to a CRT regardless of whether or not a CRT is used AFAIK


how about those nvidia 88xx cards with the HDMI ?

anyway, the original topic is really about semantics. Refresh rate can mean one of two things to a person -- how quickly the image is updated (moot in the case of LCD's, hence no flicker) or data framerate.

My guess is that the maximum framerate for a given resolution is dictated by the HDMI bandwidth limits. And whether or not an LCD manufacturer uses all the data, or tosses out frames as it has to, is unknown. I would hope that they would max it out... but then most people aren't buying these big HDTV displays for computers (although I'm in that market), so they may design them just fast enough to display 60fps in order to conform to 1080p/60.
January 19, 2007 6:04:54 PM

well, i use my monitor, which for the most part IMO beats any HDtv. you do not need HDMi or dual link DVI for 1080P.

like i say, AFAIk the gfx card still outputs the images as if it goes to a crt. I may be wrong but i think even digital signals through DVI(which is what HDMiI is based on) are still out put as whole images ready for the next "refresh". whether or not they are just converted analog signals i do not know but i don't think so.

HDMI is not anything great IMO and is no better in reality for HD then DVI. sorry i do not like the phrase HD as it is not a pc term but a terrestrial tv term and as such has no place in a pc forum. it should be referred to as WUXGA i think.

still, technically, there is no refresh rate of a LCD monitor and im sticking to that unless proven otherwise. gfx cards are not part of the monitors and so do not count.

i annoys me that they still put refresh are values in and that people use that fact as "evidence" that LCD's do have refresh rates and that higher is better.
January 19, 2007 6:06:59 PM

right, I'm agreeing with you about refresh.

but surely we can also agree that there is a maximum framerate on these units?
January 19, 2007 6:13:50 PM

yes, but that is decided by the latency no?

i understand and am well aware of the bandwidth limits of the interfaces.

i am not sure of HDMI but for dual link DVI it is 60hz @ 25 x 16. after that either the frequnecy or some other values need to drop.

still, you are right that especially at high res with a single link DVI the maximum frame rate would indeed be limited by the interface.
January 19, 2007 6:23:46 PM

yeah it's whatever you calculate from 10.2Gbps devided by color depth and resolution for HDMI 1.3.

you could introduce additional latency in between receiving the data and displaying it through some kind of processing, or even just from converting the data to a bitmap, depending on how much money they wanted to spend in fpga's or more likely some custom ASIC.. I bet for a HDTV that is supposed to conform to a minimum spec, they will deisgn it for the minimum.

Perhaps it will be only the PC monitors that will give us the maximum signal framerate that actually translates to what is displayed in the specs. Which kinda sucks but I guess I will just have to wait for it :)  But still, if you want a HDTV signal over cabletv, how do you display it on a computer monitor? I just want to buy one display, at least while I'm living in a single apartment.
January 19, 2007 6:41:22 PM

you could just get a comp monitor with multiple connections. either that or check to see if there are any tvcards that support HD cable signals.

the only problem i see is that if you get a HDtv how you would switch from tv to PC. i do not have any experience with this other than hooking up my brothers PS2 to my pc monitor using a composite cable.

all i had to do then is switch imput from the monitors options.
January 19, 2007 7:16:38 PM

yes, I think the solution I will be going for is to wait for a nice 2500x1600 monitor over 30", then get one of these Vista cable card tv tuner cards (won't be released until after Vista, because of HDCP) and just make a media PC, then use a KVM-switcher to get to the other PC.
January 19, 2007 8:02:33 PM

do you get 1080P over cable. one of the reason i do not like HD right now is because it is all low res 720P stuff or interlaced 1080i.

also, do you really need all that res :lol:  you do realise once you get a monitor like that you won't be able to go back right. i know that is how it was with me. i have to use a terrible and i mean terrible(you can create circles with just the ghosting on them) 15" LCD's at work and it is torture.
January 19, 2007 8:11:25 PM

no 1080p broadcasts anywhere as far as I know, yet anyway. It does look more and more like I should just not even order cable this year or buy a large display.

as far as the 2500x1600 -- it is quite a bit more than my current 1280x960 :)  but I am a bit of a gamer, and I do expect to have a video card eventually that can handle some nice framerates. Right now it's the 7800gtx, which is pretty good, though no HDMI. Upgrading will mean probably a new machine completely. I will probably use my current one for audio production since the audio hardware maker (Aardvark) is out of business, so no Vista support...

for me, it really is sort of a bad year to want to go all out with the home entertainment! And you know I bet after 1080p there will just be another standard necessitating yet another display.
January 19, 2007 8:17:58 PM

hmm, best put off buying a big monitor until you upgrade you gfx card unless you use old games. in newish games with full details even my x1900 struggled at times and that is at 19 x 12 so that is why i got another i corssfire.

tbh, there is no rush is there. i mean, waiting until all this HDCP and vista nonsense has settled down and new gfx cards are out would be better.

there is just so much confusion around especially if you want to make a media pc that can do home and pc entertainment. for once i recommend waiting for developments as for the last few years nothgin big has really happened in the pc world but now with vista, a new direct x APi and digital TV beginning to show its true promise, it may indeed be better to watch and wait.
January 20, 2007 5:16:28 AM

Just bought a pair of Viewsonic VX2245wm's and I am horrified to see that they only do 60hz at max res 1600/1050. My VX924 would happily do 72/75 at max res of 1280/1024.

You can totally notice a difference between 60 and 72, I'm a little peed off about these monitors, but ill have to get used to it. Was happy to see my 8800GTX running oblivion at up to 60fps outside at max res and full graphics settings with AA at 2x tho!

cheetsy
January 20, 2007 11:06:34 PM

Quote:

how about those nvidia 88xx cards with the HDMI ?


No, of course not. Thats crazy.

Its like making applications that only work on dual-core CPUs - will never happen.. or at least not for a very long time.

Quote:
Quote:

anyway, the original topic is really about semantics. Refresh rate can mean one of two things to a person -- how quickly the image is updated (moot in the case of LCD's, hence no flicker) or data framerate.


Ok, there are still some things i dont get here..

A CRT does have a refresh rate because it refereshes the whole screen at once - turns off every pixel and turns it back on with whatever value or color it may have. The CRT refreshes the screen 60 times per second, so its called 60hz (vertical refresh rate)

An LCD does not have a refresh raite because it refreshes each pixel independently and assings it one color or no color (black). Each pixel can change it's color as fast as the response time, so that is why it is the only thing that matters.

But then, why is refreshing a single pixel (wich is a function of response time) different to refreshing the entire screen of pixels (wich isn't)?

And why dosen't the LCD have a refresh rate? Is it because u cant call it that due to the fact that the whole screen isn't refreshed, but only a single pixel at a time?

Wichever it is, the only difference i see when in 60hz mode in comparison to 75hz, is mouse lag - the mouse being noticably smoother at 75hz on both CRTs and LCDs alike.
January 21, 2007 2:05:56 AM

Refresh rate - video card
Refresh rate refers to how often the picture on the screen is updated. This is independant of whatever monitor you are using (CRT, LCD, DLP, Plasma, OLED, SED, etc...).
Assume you have a 60Hz refresh rate. That means that your video card is sending a new picture 60 times per second. It is sending the entire screen 60 times per second no matter what monitor you have or whether anything has changed on your screen. The monitor then updates the entire screen every refresh rate cycle (in this case 60 times per second). Again, it does not matter what monitor type it is; they all receive an entirely new picture 60 times per second (assuming it has a refresh rate of 60Hz).
Refresh rate - games/updating
Ignoring the specific issues of flickering on CRT monitors, refresh rate does have an effect on other things -- such as games and fast moving objects. As described earlier, refresh rate is simply how often a new (up-to-date) picture is sent to your monitor. If the refresh rate was too slow, then there would be a noticeable difference between what you did on your computer and what you see on your monitor. 60Hz (or 60 frames per second) is usually enough for most tasks. However, some very demanding users may be able to notice (and use) higher refresh rates like 75Hz for things like having that split second extra faster update in a game.
CRT flicker - the connection to refresh rate
It seems that many people perceive refresh rate as controlling the flicker on CRT monitors and assume that refresh rate has no affect on other monitor types like LCD; however this is not the case. Although there isa strong link between refresh rate and flicker, flicker on CRT monitors is a totally different issue from refresh rate. The concept of refresh rate has already been explained... so now on to the topic of CRT flicker.
Flicker on a CRT monitor is the result of how CRT monitors produce a picture. On a CRT, the electron gun fires electrons at the screen that causes the pixels to light up for a split second, after which, the screen immediately starts to fade back to black (no light). On a CRT, the picture goes in a cycle: the screen updates, the picture starts to fade back to black, the screen updates again (restoring the color), it fades back to black, and so on, and so on. A CRT simply cannot hold a constant picture; it must continually update to keep going. The slower this update, the more noticeable the period between updates (where the monitor starts to fade back to black). When the update is too slow, many people can notice the fading of the picture back to black between cycles (whether subjectively by getting a headache or objectively by knowing what they are looking at).
How does this relate to refresh rate? Since, as explained earlier, refresh rate is simply how fast a new picture is sent to the monitor, then that means if you have a lower refresh rate being sent to the CRT monitor, then the flicker (color, black, color transition) will be more noticeable; but if you raise the refresh rate, the CRT monitor will update more often and reduce how much you notice the flicker. So, as you can see, refresh rate is important to using a CRT monitor, but it is not something unique to CRT monitors.
Refresh rate and LCD monitors
On an LCD, things are completely different. The light comes from a constantly lit "white" bulb in the back of the monitor. In front of the bulb is a "screen" with millions of little LCD pixels on it. This is the part you see; it is the part that shows the picture.
Again, refresh rate comes into play. Whatever the refresh rate is, that is how often the LCD screen will change to show whatever the computer looks like now. Between refreshes, nothing happens. The LCD pixels stay the same... the backlight remains turned on... etc.... It is a constant picture that does not fade back to black like on a CRT. Thus, you should not see any flicker effect from this.
However, as described earlier, refresh rate is still how often a new picture is sent to your monitor, and it may have some impact in some rare cases.
Response time
While refresh rate has to do with the computer and how often a picture is sent to the monitor, response time is entirely a monitor issue. All monitors have a response time. Response time is the measure of how long it takes your monitor to change the picture (each time it is told to during each refresh cycle). Unfortunatly, LCD monitors have slow reponse times, causing them to change the picture slowly. For fast motion, this produces a blurring effect instead of sharp, distinct moving objects.
Now... assuming that you used a refresh rate of 60Hz, that means that you need to change the picture every 16.6 milliseconds. Thus, an LCD that is slower than 16.6ms is gonna have blurring in it. On the other hand, if you need the faster frame rate of something like 75Hz/FPS, then that would require updating the picture every 13.3 milliseconds. (Note: it is my guess that monitors actually need much more than these bare minimum numbers being mentioned.) So..., if the monitor's response time is not fast enough, then it doesn't really matter how high you set the refresh rate.
[code:1:4a78c69816]If you are interested, a refresh rate of 60Hz = 60 frames sent to the monitor per second. As you may have noticed, LCD monitors are often rated with a response time of so many milliseconds, or ms for short. One millisecond is 1/1,000th of a second. Doing a little math, we find that to achieve 60 frames per second refresh rate, would require updating the monitor around every 16.6ms (1,000/60=16.6).[/code:1:4a78c69816]
January 21, 2007 6:01:08 PM

Thank You, that was very interesting.

So ur saying that LCD infact DO have a refresh rate, but dont have a flicker because the LCD is always lit unlike the CRT.

So then why cant LCDs do more than 60hz at resolutions above 1280x1024?

It cant be because of the response time, since there are monitors that have 2ms response times, and mine has 8ms wich is more than enough 75, or even 85hz..

Oh and, what is the response time for CRTs, and why is it higher?
January 22, 2007 11:30:49 PM

bump
January 23, 2007 12:12:05 AM

Quote:
Thank You, that was very interesting.

So ur saying that LCD infact DO have a refresh rate, but dont have a flicker because the LCD is always lit unlike the CRT.

In theory, yes; though I don't know if there's any type of flicker when the LCDs attempt to change each refresh cycle. BTW, I have read that the lamps used in LCD monitors do actually flicker, but it is over 1,000x per second. Although you cannot see such flicker, some people have noted having problems with the lamps used in some older LCD monitors, whether it be because of their fast flicker or something else. On the other hand, I have seen LCD monitors in a store that were flickering (perhaps where the lamp was bad)?

Quote:

So then why cant LCDs do more than 60hz at resolutions above 1280x1024?

It cant be because of the response time, since there are monitors that have 2ms response times, and mine has 8ms wich is more than enough 75, or even 85hz..

Actually, you can't really think of it the way I described. Sorry about that. 60Hz means it would change every 16.6 milliseconds, right? But, if the monitor takes 16 milliseconds to change the pixel to the right color, then by the time it has reached the right color, it has to change again.... So for 16 milliseconds you see the pixel go through a gradual transition from the color it was to the new color, and by the time it gets where it's supposed to be it is almost time to start the process of changing to another color again! So, you hardly get to see the right color, just a big blurr. What does this mean? I suspect it means that the response time needs to be much lower than what is needed to match the refresh rate - at least in order for you to see the right color long enough. However, this is only a theory. I do not understand the details enough myself to say for sure.

Quote:
Oh and, what is the response time for CRTs, and why is it higher?

Don't know myself, but it's low enough that you don't see any blurring. CRTs are a different technology.

You might find this interesting:
http://www.xbitlabs.com/articles/other/display/lcd-guid...
Take note of the last paragraph and the two images.
January 23, 2007 2:04:49 AM

Quote:

So then why cant LCDs do more than 60hz at resolutions above 1280x1024?

It cant be because of the response time, since there are monitors that have 2ms response times, and mine has 8ms wich is more than enough 75, or even 85hz..

Actually, you can't really think of it the way I described. Sorry about that. 60Hz means it would change every 16.6 milliseconds, right? But, if the monitor takes 16 milliseconds to change the pixel to the right color, then by the time it has reached the right color, it has to change again.... So for 16 milliseconds you see the pixel go through a gradual transition from the color it was to the new color, and by the time it gets where it's supposed to be it is almost time to start the process of changing to another color again! So, you hardly get to see the right color, just a big blurr. What does this mean? I suspect it means that the response time needs to be much lower than what is needed to match the refresh rate - at least in order for you to see the right color long enough. However, this is only a theory. I do not understand the details enough myself to say for sure.

But the pixel has 60 times to refresh per second, even at 16.6ms.
There is no way that a pixel would need to refresh more than 60 times per second, so i dont get what u mean when u say that it has to be less than 16.6ms for 60hz because the pixel is constantly changing.



And also, why is it that LCD can only do 60hz at a resolution of 1600x1200 or above?
January 23, 2007 2:37:05 AM

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But the pixel has 60 times to refresh per second, even at 16.6ms.
There is no way that a pixel would need to refresh more than 60 times per second, so i dont get what u mean when u say that it has to be less than 16.6ms for 60hz because the pixel is constantly changing.

60Hz means that every 16.6, the screen is supposed to show a new picture. So, it goes like this... (to make things easier, let's round it off to every 17ms)
0ms = Video card sends the picture.
0ms = Monitor tells all the pixels on the screen what the new picture looks like and the pixels start to change.
(At this point, assume that the screen is currently black and the monitor is being told to change to white; also let's assume that the monitor has an exact response time of 16ms. So...)
1ms = all the pixels on the monitor are now 1/16th of the way from changing from black to white; that means the pixels are now currently a very dark grey.
8ms = getting closer to white... the monitor is now a neutral grey color
12ms = much closer... the monitor is now a light grey
16ms = white... the monitor has finally switched to white
17ms = a new picture is sent to the monitor.... this time telling it to change back to black...
18ms = transition is starting back to black.... color is still near white
20ms = transition still going... color is greyish
33ms = transition done... monitor is finally black again

So... what does this mean.... During this time, the monitor was only supposed to show three frames: 1 black frame to start with, then 1 white frame, then 1 black frame. Instead... due to the response time, the monitor showed 1 black frame for 1ms, various shades of grey for 16ms, one white frame for 1ms, various shades of grey for 16ms, then 1 black frame for 1ms.
So... for only a small percentage of the time (less than 10%) did you see the correct picture.... The rest of the time you were seeing shades of grey (the wrong color). In all likelihood this means you are going to see the picture as greyish, blurred, or some other weird effect, and not the correct 1 frame of black, 1 frame of white, and then one frame of black.

Applying this to the real world, this appears to explain exactly what you see on LCD monitors -- the blurring and smearing that you see even on very low response time monitors (even ones lower than the refresh rate match) as shown on the last picture on this page: http://www.xbitlabs.com/articles/other/display/lcd-guid...



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And also, why is it that LCD can only do 60hz at a resolution of 1600x1200 or above?

Don't know.
January 23, 2007 6:48:13 AM

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Thank You, that was very interesting.


Oh and, what is the response time for CRTs, and why is it higher?


The response time for CRT's (cathode ray tube) is higher because the of the way it works. An electron gun shoots, you guessed it, electrons at phosphors inbedded into "pixels", these are the polygons you see when you look closely at a crt, there are red blue and green phosphors in each polygon. When the electron or cathode ray gun hits the phosphors with electrons they glow different colors depending on what the signal tells the ray gun to produce. Once the beam has hit the phospors they almost immediately stop glowing. Therefore the response time of a CRT is basically instantaneous. It takes at least less than 1/1000th (est) of a second for the phosophor to stop glowing (moniters at resolutions of 1280x1024 edit:can have up to 120hz refresh rates, therefore the response time is greater than 120hz). This is good because the ray gun refreshes the screen at >60hz, so if the phosphors did not stop glowing nearly instantly than the CRT would be unable to reach higher refresh rates because you would have to add the time it takes for the phosphor to lose its charge or stop glowing. That is why CRT's have a faster response time than LCD's, because phosphors glow when hit with electrons and stop glowing when they are not hit by electrons, LCD's require the crystals to rotate to refract the color of light it needs to produce at any given moment. Even the fastest LCD's will likley not match the response time of CRT's simple because of the mechanical limitations of LCD's. A 2ms rated LCD only seems to not produce ghosting because its pixels can move a faster rate than our eye's can detect, for most its 60hz, for me its about 85hz. That leave LCD's to produce ms rates less than 1ms so that ghosting is percieved to be equal to CRT's.


So thats why CRT's have a faster response time and no ghosting.
January 23, 2007 7:10:49 AM

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So then why cant LCDs do more than 60hz at resolutions above 1280x1024?



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there are two main reasons:

1. Connection Limitations: A single DVI digital connection has limited bandwidth... not enough to allow higher than 60Hz refresh rate at full 24bpp Color Depth for all resolutions, so typically all resolutions on LCD monitors using DVI are capped at 60Hz. If you use a VGA analog connector instead, you can often select a refresh rate higher than 60Hz on an LCD, though again nowhere near the theoretical refresh rate limit based on your response time, partly because of the reason below...

2. Monitor Limitations: LCD manufacturers want to ensure that their monitors function satisfactorily in all situations, particularly since they often overstate response times. So typically they set the maximum supported refresh rates on their monitors such that they are relatively conservative and can meet the challenge of refreshing the entire screen as often as required in any situation without any ghosting. Furthermore, setting too high a refresh rate on an LCD, even if it's available, can actually result in problems in certain games and applications due to timing issues. So for reliability and compatibility purposes, LCD refresh rates are not as high as they could theoretically be.


TweakGuides.com




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Oh and, what is the response time for CRTs, and why is it higher?


toms hardware measured 860 microseconds = .86ms (thats for all shades?)


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i notice a HUGE difference beetween 60hz and 75hz in my LCD monitor (connected by a VGA cable), so whats up?


just a guess: overdrive errors are reduced at 75hz - at a cost:

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So running at 75Hz causes the RTC [overdrive] control to function incorrectly, reducing responsiveness, but having the positive effect that RTC errors / overshoot are reduced. Benoit Dupont over at Tom's Hardware also noticed that the artefacts and overshoot on some RTC enabled monitors was reduced by moving away from the 60Hz recommended refresh rate:



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On displays with which the overdrive is poorly controlled, some people can see visual artefacts in FPS games during lateral movements. A halo of colour appears temporarily around the moving object. This phenomenon is due to the overdrive technology used on this type of monitor. In the worst cases, the colour displayed is not the right one for 3 whole frames, which can be visible in the form of unwanted colours. (If you have this problem, one trick that works fairly well is to increase your display's refresh rate to 70 Hz instead of 60 Hz.)


TFT Central


so you'll get no more than 60hz on an LCD (and usually much less because of something called LCD image delay...a whole nother topic you can read here)
January 23, 2007 7:33:39 AM

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I suspect that the response time needs to be much lower than what is needed to match the refresh rate - at least in order for you to see the right color long enough. However, this is only a theory.



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In LCDs, each pixel emits light of set intensity for a full period of 20 ms (in this example), plus the time it takes for it to switch to the next state, typically 12 to 25 ms.


so to get 60hz on the LCD they tested you need a response time around minus 3.4 ms (16.6 - 20 = - 3.4 ms), which is of course impossible. link
January 23, 2007 12:37:55 PM

Alright, but its still somewhat confusing..

You say that it takes 16ms for the whole screen to turn from black to white, but what abt each individual pixel? I thought that LCDs refresh each individual pixel at a time, unlike CRTs. I was thinking of "response time" to have to do with LCDs and single pixels, while "refresh rate" to do with CRTs and the entire screen.

And you say that it takes 16ms for that pixel to turn from black to white, but i did not realize that it has to turn into dark gray, then light gray, etc. I thought it was just black - white.
That is not what happens with CRTs, right? They can get from black to white in 1ms or so.

And then ur saying that since it takes so long to get from black to white, and that it has to go through shades of gray, that u see blurring because of this? So a CRT that has a response time of 0.86ms would be changing to white so quickly, that there would be much less shades of gray, and that would somehow reduce blurring? And if so, then how?


I dont know abt the 75hz being being smoother because of overdrive error reduction.. i cannot see a difference beetween my CRT and my LCD at both 60hz and 75hz.. not to mention 85hz in wich i can see no difference.


And lastly, if an LCD had a refresh rate of 30hz or less, would it hurt my eyes or would it not because it has no flicker?
January 23, 2007 4:13:32 PM

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Alright, but its still somewhat confusing..

You say that it takes 16ms for the whole screen to turn from black to white, but what abt each individual pixel? I thought that LCDs refresh each individual pixel at a time, unlike CRTs. I was thinking of "response time" to have to do with LCDs and single pixels, while "refresh rate" to do with CRTs and the entire screen.

Just simplifying it. Technically, it is subpixels that are changing (the red, green, or blue subpixel). If the entire screen is black and is changing to white, that means every single sub-pixel on the screen is changing from darkest to brightest.

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And you say that it takes 16ms for that pixel to turn from black to white, but i did not realize that it has to turn into dark gray, then light gray, etc. I thought it was just black - white.
That is not what happens with CRTs, right? They can get from black to white in 1ms or so.

The electron gun sends the right color imediately.... There is no transition period. It is the right color right away. However, afterwards, there is a fade off time, but it is very fast.

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And then ur saying that since it takes so long to get from black to white, and that it has to go through shades of gray, that u see blurring because of this? So a CRT that has a response time of 0.86ms would be changing to white so quickly, that there would be much less shades of gray, and that would somehow reduce blurring? And if so, then how?

I have no idea what the real response time on CRT monitors is. According to some, it appears that the real issue with LCDs is the fact that the picture does not immediately fade away between refresh cycles like on LCD monitors:
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Even for the current fastest LCDs, images displayed are complete and without transition between each of them. Even if the crystals are very fast, our eye keeps the previous image in memory. In consequence it adds an afterglow that the monitor doesn't actually produces. This point, added to other factors, disturbs response time measures. This is the reason why they are so less representative of the monitor real reaction time.
http://www.behardware.com/news/lire/09-03-2006/


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I dont know abt the 75hz being being smoother because of overdrive error reduction.. i cannot see a difference beetween my CRT and my LCD at both 60hz and 75hz.. not to mention 85hz in wich i can see no difference.
Not all monitors have overdrive; and for those that do, not all of them have overdrive errors that are very noticeable. So, this statement cannot apply to all monitors.


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And lastly, if an LCD had a refresh rate of 30hz or less, would it hurt my eyes or would it not because it has no flicker?
Not because of refresh rate flicker. It could be 1Hz, and you would see no refresh rate flicker.
January 24, 2007 12:11:38 AM

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Alright, but its still somewhat confusing..

You say that it takes 16ms for the whole screen to turn from black to white, but what abt each individual pixel? I thought that LCDs refresh each individual pixel at a time, unlike CRTs. I was thinking of "response time" to have to do with LCDs and single pixels, while "refresh rate" to do with CRTs and the entire screen.

Just simplifying it. Technically, it is subpixels that are changing (the red, green, or blue subpixel). If the entire screen is black and is changing to white, that means every single sub-pixel on the screen is changing from darkest to brightest.

So is it one pixel per time, or the whole screen, on LCDs?

How can red, blue and green subpixels make a white pixel? u need more than 3 colors, or they would need to be the 3 main colors, where yellow would be instead of green.
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And you saying that it takes 16ms for that pixel to turn from black to white, but i did not realize that it has to turn into dark gray, then light gray, etc. I thought it was just black - white.
That is not what happens with CRTs, right? They can get from black to white in 1ms or so.

The electron gun sends the right color imediately.... There is no transition period. It is the right color right away. However, afterwards, there is a fade off time, but it is very fast.

Alright, but on LCDs, how come it changes from black to grey and only then to white? Why cant it change from black to white without turning into shades?
Is it because the pixels do not turn off, and need to change in order to become something different, other than a CRT where they are turned off and then on in lightning speed?

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I dont know abt the 75hz being being smoother because of overdrive error reduction.. i cannot see a difference beetween my CRT and my LCD at both 60hz and 75hz.. not to mention 85hz in wich i can see no difference.
Not all monitors have overdrive; and for those that do, not all of them have overdrive errors that are very noticeable. So, this statement cannot apply to all monitors.

So why DOES it feel smoother?

I went back to my CRT and noticed that it was actually a lot smoother than the LCD.. Would the LCD feel as smooth with a lower response time?
January 24, 2007 1:24:34 AM

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So is it one pixel per time, or the whole screen, on LCDs?

How can red, blue and green subpixels make a white pixel? u need more than 3 colors, or they would need to be the 3 main colors, where yellow would be instead of green.
...
Alright, but on LCDs, how come it changes from black to grey and only then to white? Why cant it change from black to white without turning into shades?
Is it because the pixels do not turn off, and need to change in order to become something different, other than a CRT where they are turned off and then on in lightning speed?

Ignore the example given above for right now. An LCD monitor is made up of millions of pixels. These are the individual "dots" that make up the picture you see on the screen. However, each "pixel" is actually made up of 3 separate pixels (or sub-pixels): 1 red, 1 blue, and 1 green. The human eye can produce most of the colors you see by combining various shades of red, green, and blue (though not all colors like neon and stuff like chrome or gold). So, a computer monitor simply displays various intensities of red, green, and blue to produce a single color for 1 pixel. For example, full bright red, green, and blue, become white; whereas, full bright red and green, but no blue produces yellow.
Technically, response time is the measure of approximately how it long it takes one of these subpixels LCDs to change from one state to another.
Now, to explain why the process is not instantaneous, you have to understand how LCDs work. LCDs work by filtering light. In other words, there is a backlight behind the LCD display that provides a constant light source. Then light then shines through the LCD screen where it is filtered through the millions of red, green, and blue subpixels to produce an image. It is the LCD subpixels that change to produce a picture. These LCD subpixels must physically change their shape in order to block or allow more light through. (By blocking or allowing more light, they can produce various shades or intensities of color.) However, like any object that must physically move, LCDs take time to move or change their shape. This is where the response time comes in. It is a measure of how long it takes the LCD subpixels to physically change their shape. However, if a pixel wants to change from white to black it must physically twist itself all the way from white to black, thus passing by all the other shades along the way.





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So why DOES it feel smoother?

I went back to my CRT and noticed that it was actually a lot smoother than the LCD.. Would the LCD feel as smooth with a lower response time?

I can't really say for sure. Some manufacturers and reviewers are starting to claim that the reason for this is image persistance as perceived by you brain that occurs only on LCD monitors; in other words, it is not response time anymore. It has also been shown on one model that raising the refresh rate to something like 100Hz helps solve the problem. However, I still am not satisfied with the explanations that I have read on this topic to know what the real answer is or whether this is 100% accurate.
January 24, 2007 11:34:06 AM

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no 1080p broadcasts anywhere as far as I know, yet anyway. It does look more and more like I should just not even order cable this year or buy a large display.

And you know I bet after 1080p there will just be another standard necessitating yet another display.


There won't be 1080p broadcast any time soon... the bandwidth requirement is simply too great. HD @ 720p is still terrific.
February 9, 2007 4:44:38 PM

Track,

Can I ask for more information on how you feel, please? At the start, you say it makes a "HUGE" difference, but later on your reporting of the impact seems, in your writing, to be not as drastic.

I ask, as I have an issue at work with someone who is reporting trouble viewing a Dell LCD at 60Hz, but not 75 ... the result is that it has started me on a mini-crusade. Although I have five different "manufacturers" of screen, it doesn't help that I would have to take them apart to find out the true manufacturers.

I am noticing the effect (on some of the monitors) of the smoother mouse, but larger operations like scrolling text or dragging windows seem the same to me in either rate. Also, a variety of other people I know who have various eye conditions and whos lives were made a misery by CRT's, are totally fine with the LCD's.

So ... Track ... as someone who is sensitive to this refresh rate on LCD's, may I ask you how deeply you are affected?

All the feedback from Dell, the HSE and others, say that this is the first time they have heard of discomfort caused by LCD's and although Dell have given me a statement to the effect that there is no difference, I have asked them to go back to the designers who built the things.

However, from what other, obviously educated, people have said here, this is starting to look like being a situation which is individual to the true manufacturer of the monitor and possibly the control mechanisms employed (I used to repair laptops very often and saw some differences in control circuitry, I also spent some time in Sony and Telewest, quizzing the senior engineers; although it would take a component level technician to be able to explain the mechanisms.) Slight hint ... never touch the voltage inverter :-)
March 1, 2007 8:55:48 PM

Lots of text here and I think I read everything.

My question: If a LCD has a maximum refresh fate of 60MHz at a particular resolution, and if you are getting a frame rate from your FPS of say 75FPS, really you are only seeing 60FPS?

Is VSYNC used to help situations where the FPS > Refresh rate?

-Deuce-
March 1, 2007 11:51:48 PM

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Lots of text here and I think I read everything.

My question: If a LCD has a maximum refresh fate of 60MHz at a particular resolution, and if you are getting a frame rate from your FPS of say 75FPS, really you are only seeing 60FPS?

Is VSYNC used to help situations where the FPS > Refresh rate?

-Deuce-

Yes, you will still only get 60FPS.
Turning off Vsync can help a little if the frame rate is note quite as fast as your monitor's refresh rate (so that it will send part of the data instead of waiting for the next refresh cycle). It does nothing it your FPS is always above the refresh rate (which as you know, in real life, the FPS can go up and down across the course of a game).
November 1, 2007 3:17:44 PM

Okay, I want everyone to understand how an LCD really works. I haven't read everyone's comments, but I did see that there were some comments that talked about how it worked, but not in great detail.

To start off, refresh rate does not apply to LCDs. I know this has been stated already, but it doesn't. It doesn't apply at all. LCDs work completely different in all ways than CRTs do. CRTs (Cathode ray tubes) scan the screen with a ray that causes the phosphors to glow (definition of phosphors from www.mtw.pwp.blueyonder.co.uk/weddell/guide/gloss1.html: Chemicals which glow when struck by a beam of electrons.) So the ray (beam of electrons) scans across the screen, from the top to the bottom, and from left to right, causing each pixel to light up, and it continues to do this over and over so that you see a constant picture.

Now an LCD works like this. There is actually an electrode grid that powers electricity (a very minimal amount of electricity) to each pixel on the screen. However, power is only sent to a specific pixel if you want the pixel to be black, or dimmer. With no power sent to it, you will see light. Now this makes no sense unless you understand how an LCD works.

How an LCD works
First of all, LCD stands for Liquid Crystal Display. Each Liquid crystal either allows light to pass through it or it doesn't. It's not "On or off" it's more like open or closed. But it's not even that (but that's where things get more complicated and if you want a full understanding, then go to this site http://www.howstuffworks.com/lcd.htm).

Second, LCDs have two light bulbs, or light tubes, on the sides of the screen. In the small area on the sides of your screen, these two light tubes are placed, and they supply light to the back of the LCD panel. From there, they reflect outward to you. However, they only do this if the Liquid crystal is "open" (it's actually twisted, but you'll have to read the site that I showed above to understand that, so we'll just say open or closed to make it simple) Now, if you want to make a pixel black, you apply electricity to it, and it closes (or untwists) the liquid crystal (or pixel).

Third, since each pixel is independently controlled by the electrode grid, they aren't "refreshed." This is where "response time" comes in. Response time isn't quite related to "refresh rate." Many people think that, but what it really is is how fast the monitor can register the movement of something on the screen, and actually tell those pixels to change to reflect the movement. So, if you move your mouse, it tells the pixels to change to show your mouse movement. If you have a slow response time, then the mouse will act as if it is lagging behind. (definition of response time from www.acuityresearch.com/Resources/glossary.shtml: The delay between the time of a change in the target position and the time the sensor's output changes.) The lower the response time, the faster the monitor outputs the movement of something on your screen.

Conclusion
So, in summary, refresh rate doesn't have anything to do with LCDs because they are always either allowing the light to pass, or not. It would be like looking at a florescent light bulb and saying that it is refreshing. It's just sending out light all the time, not refreshing. And your lcd monitor isn't sending pulses to the pixels telling them to close, then open, then close, then open. So you will never see "flickering" on an LCD. (And I do understand flickering. To me it looks more like "glaring" though. 60hz on a CRT is very noticeable to me. I can even somewhat tell the difference between 75hz and 85hz.)

Any questions? Please ask and I will answer them.

As for gaming? I haven't researched it, so I can't refute this, but I guess it may be possible that the game will only send through the amount of fps as your hz is set on your computer. However, 60fps is tons faster than most people can register anyway (in my opinion, maybe I'm wrong. I haven't done research yet). Movies are only at 30fps.
November 2, 2007 1:19:48 PM

I'm confused by what I read here. Too many people are contradicting too many things. I have a 24" Acer AL2423W LCD monitor that hurts my eyes. I tried to increase the refresh rate (which I'm learning might mean ziltch), but found it can only be 60 Hz. Should I be looking for a 75-85 Hz LCD monitor to replace my Acer, or will that not mean a thing in aiding my sore eyes?

Because the strange thing is..why do monitor manufacturers even mention the amount of Hz the refresh rate of the LCD monitor is capable of, if it doesn't mean anything? When I e-mailed Acer about my 60 Hz monitor, they said they do have some 75 Hz monitors, if I'd like to look through those. Why would Acer even suggest that, then, if it doesn't mean anything?

Thank you
November 2, 2007 2:16:59 PM

That's a good question. I'll have to research that. Sounds to me, though, that you may have a cheap monitor. I have seen many LCD monitors, all on 60hz, and none of them flicker or anything. My eyes are very sensitive to CRT 60hz. I can tell the difference easily between 60 and 75hz. So, it may just be that you have a cheap LCD that for some reason flickers. But it would be flickering for a different reason than hz, in my opinion. I'd really like to see your LCD monitor though.

As for Acer suggesting an LCD monitor with higher hz, it may just be a marketing scheme. They may be playing off of people's lack of knowledge of how LCDs work in order to sell higher priced LCDs. Sounds strange to me. Maybe I'll call them up and ask them myself.

I called Acer, this is what they said
So I did call up Acer right after I wrote the above statements. I asked the guy about whether or not they sold monitors with higher refresh rates. He at first said they didn't, but he checked and found out they did, but he didn't understand why it would matter, because he also knew that refresh rate doesn't apply to LCDs (so maybe it was just for the gaming issue - that you can't get a higher fps than your video card sets the refresh rate to).

However, he did say that your monitor may be hurting your eyes because either your resolution isn't set to it's native resolution, or your brightness is too high. If the resolution isn't set right, then it will make your monitor a little blurry, and that could hurt your eyes. Also, a low viewing angle may do it. It may have just come a little blurry because of a manufacturing defect.

These are all just assumptions though, because we don't know what is actually causing your eyes to hurt. Let me know that and maybe I can assist further. Does it look like the monitor is flickering? Does it look a little blurry? What's up?.


Latest I've learned is smoothness
The latest I've learned about lcds and refresh rates is that it is possible that a higher refresh rate could result in smoother motion. This means that when you move your mouse, it may move smoother, or something like that. But, it would not cause your monitor to flicker at a lower refresh rate. As for the smoother motion, I have an LCD that supports up to 75 hz, and I can't tell a difference between them when moving things on my screen. But perhaps I'm not accustomed to it. I don't know.
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