can someone explain refresh rates to me

[w00t]

Can someone please explain lcd and crt refresh rates? does it have anything to do with frames per a second if the Hz is higher do you see more frames per second?

edit: googling right now.

"The refresh rate is the number of times a display's image is repainted or refreshed per second. The refresh rate is expressed in hertz so a refresh rate of 75 means the image is refreshed 75 times in a second. The refresh rate for each display depends on the video card used. You can change the refresh rate in the display properties. However, if you change the refresh rate to a setting that the display or video card cannot support, the display goes blank or the image becomes distorted. It is recommended to consult the display and video card manuals before changing the settings to determine the supported refresh rates."

so if you have your monitor at 100Hz you can see 100frames per a second correct? so why do people get lcd's that have a max of like 85 and some res only support 60Hz?

edit: update

"Note: Do not confuse the refresh rate with the term "frame rate", often used for games. The frame rate of a program refers to how many times per second the graphics engine can calculate a new image and put it into the video memory. The refresh rate is how often the contents of video memory are sent to the monitor. Frame rate is much more a function of the type of software being used and how well it works with the acceleration capabilities of the video card. It has nothing at all to do with the monitor.

The refresh rate is important because it directly impacts the viewability of the screen image. Refresh rates that are too low cause annoying flicker that can be distracting to the viewer and can cause fatigue and eye strain. The refresh rate necessary to avoid this varies with the individual, because it is based on the eye's ability to notice the repainting of the image many times per second. My experience has generally been as follows: "

ok its starting to make since. what about ms times? for lcds

 

[ChuckHsiao]

CRTs work by firing electrons at a phosphorescent screen. The screen then glows, producing the image, then very quickly (< 1 ms) fades. The refresh rate is how many times per second this occurs.

LCDs work by placing an electronic shutter (the LCD part itself) over a constantly-on fluorescent light (often called the backlight). The shutter controls what percentage of the light gets through at every pixel, hence producing the image. The refresh rate for LCDs specifies how often the shutter is given new instructions for changing how much light is let through.

So the refresh rate has the same meaning for both CRTs and LCDs. In either case, it's specifying how many images the monitor can display per second (measured in hertz or Hz, which means "how many times per second"). However, because of how they work, its consequences are different. For a CRT, most of the time is spent in the "off" (i.e. black) state, since the screen loses its glow very quickly. Thus, at a low refresh rate, the fact that it's actually flashing becomes noticeable; not only that, but each flash has to be brighter in order to maintain the same overall (time-averaged) brightness, which from my understanding is what causes eye-strain. Thus you need it to run at say 75 to 100 Hz or so, depending on how much your individual eyes are affected by this. For LCDs, however, the backlight is always on, so there are no flicker issues, and hence a 60 Hz refresh rate is sufficient.

For LCDs however what's important is response time. The refresh rate is how many times per second instructions are given to the shutters to change the brightness; however, the shutters don't react instantly, but need some time to change to their new amount. This is the response time. It is measured in milliseconds, or ms. Keep in mind that 60 Hz is 16.7 ms. Unfortunately, as with any new industry, there's a glut of manufacturers making all sorts of claims about response times in order to get more customers. In theory, a monitor that's *true* 16 ms (i.e. takes 16 ms or less to get from one state to any other state for all states) is good enough*, since that's below the refresh rate (60 Hz). In practice, a claim of 16 ms can mean up to 50 ms or more for some transitions, etc., which becomes very quickly noticeable, since the figure can mean black-to-white-to-black (the standard definition), which isn't particularly practical because we usually use our monitors in shades not black/white; or gray-to-gray, which has no standard definition so manufacturers are free to make up their own way of measuring it, and unsurprisingly, choosing whichever measurement allows them to justify the lowest numbers possible. Compounding the problem further, the actual response time varies (greatly) depending on what initial and final brightnesses you're testing, so it's not really true to simplify all that down to a single number, hence manufacturers choose whichever one they can get away with. Ahh well.

* There's some qualifications with this statement (since there's also issues like image retention in the eye) but addressing them quickly makes this a lot more complicated, heh.

 

[w00t]

Originally posted by: ChuckHsiao
CRTs work by firing electrons at a phosphorescent screen. The screen then glows, producing the image, then very quickly (< 1 ms) fades. The refresh rate is how many times per second this occurs.

LCDs work by placing an electronic shutter (the LCD part itself) over a constantly-on fluorescent light (often called the backlight). The shutter controls what percentage of the light gets through at every pixel, hence producing the image. The refresh rate for LCDs specifies how often the shutter is given new instructions for changing how much light is let through.

So the refresh rate has the same meaning for both CRTs and LCDs. In either case, it's specifying how many images the monitor can display per second (measured in hertz or Hz, which means "how many times per second"). However, because of how they work, its consequences are different. For a CRT, most of the time is spent in the "off" (i.e. black) state, since the screen loses its glow very quickly. Thus, at a low refresh rate, the fact that it's actually flashing becomes noticeable; not only that, but each flash has to be brighter in order to maintain the same overall (time-averaged) brightness, which from my understanding is what causes eye-strain. Thus you need it to run at say 75 to 100 Hz or so, depending on how much your individual eyes are affected by this. For LCDs, however, the backlight is always on, so there are no flicker issues, and hence a 60 Hz refresh rate is sufficient.

For LCDs however what's important is response time. The refresh rate is how many times per second instructions are given to the shutters to change the brightness; however, the shutters don't react instantly, but need some time to change to their new amount. This is the response time. It is measured in milliseconds, or ms. Keep in mind that 60 Hz is 16.7 ms. Unfortunately, as with any new industry, there's a glut of manufacturers making all sorts of claims about response times in order to get more customers. In theory, a monitor that's *true* 16 ms (i.e. takes 16 ms or less to get from one state to any other state for all states) is good enough*, since that's below the refresh rate (60 Hz). In practice, a claim of 16 ms can mean up to 50 ms or more for some transitions, etc., which becomes very quickly noticeable, since the figure can mean black-to-white-to-black (the standard definition), which isn't particularly practical because we usually use our monitors in shades not black/white; or gray-to-gray, which has no standard definition so manufacturers are free to make up their own way of measuring it, and unsurprisingly, choosing whichever measurement allows them to justify the lowest numbers possible. Compounding the problem further, the actual response time varies (greatly) depending on what initial and final brightnesses you're testing, so it's not really true to simplify all that down to a single number, hence manufacturers choose whichever one they can get away with. Ahh well.

* There's some qualifications with this statement (since there's also issues like image retention in the eye) but addressing them quickly makes this a lot more complicated, heh.

thanks.

 

[w00t]

Can having an lcd affect your gaming response time? if it has a 25ms response time that is 1/4 of a second if it was to stay at 25ms response time which it wouldnt. so you could be up to a half a second off? right that could be life or death

 

[dsj]

Does the refresh rate affect the frame rates in games?

 

[w00t]

Originally posted by: dsj
Does the refresh rate affect the frame rates in games?

read the post.

 

[ChuckHsiao]

Yes it can affect your gaming reflexes; people buy the fast LCDs specifically for this purpose. On the other hand, it just fuels manufacturers' incentives to find any way to deflate (heh) their response time numbers. Also, having a fast response time tends to mean sacrifices in color quality, viewing angle, etc. So it's clear there's still work to be done.

On the other hand, 25 ms is 1/40 of a second (not 1/4), and the refresh rate is usually 16 ms (1/60 of a second). So if your reflexes are affected by that, then you should look for something better. The problem with this is that a 25 ms rated monitor is rarely actually 25 ms. So to get a gaming monitor, you do have to go with something lower, like say 12 ms or 8 ms.

A monitor's refresh rate does somewhat affect a game's frame rate, in that there's no point in having more frames than what the monitor can display -- they simply get skipped. So if your game has a frame rate of 85 frames a second, but your monitor is running at 75 Hz, then ten frames per second are simply getting skipped by the monitor (more accurately, I think the video card simply skips ten frames from being passed to the monitor, since it knows that your monitor is set to run at 75 Hz). Otherwise though as mentioned in the article, a game's frame rate is simply how many times a second the game's internal state is being calculated, regardless of how often that information is actually being passed to the monitor for display.