I've been researching LCDs to buy one and there's something that has been bothering me. Everywhere I've read, it says LCDs are better for your eyes because they have better refresh rates. I made a comparison the LCD I ordered (Imagequest L90D+) which has a max refresh rate of 75hz. My 21" Cornerstone CRT is able to do up to 85hz. So since my CRT can write faster to the screen, is it not better for my eyes?
LCD vs CRT refresh rates
- Thread starter DPolishSensation
- Start date
I believe it's because LCDs don't actually refresh. A CRT redraws the entire screen with a new frame, hence the term framerate/refresh rate. Thus, if you run at 60 Hz refresh rate, your eye sees 60 new frames every second. LCDs don't refresh in this way - they simply change the color of the pixel as it needs updated. If an LCD has a 16 ms response time, then it checks for pixel updates every 16 ms, meaning it can effectively render 62.5 frames per second.
In other words, a CRT has many frames flipping by that your eye considers as a stationary image, but this is not the case. An LCD actually maintains the image so your eyes don't have to worry about the constant motion from a CRT. Not the best explanation, but hopefully you get the idea.
In other words, a CRT has many frames flipping by that your eye considers as a stationary image, but this is not the case. An LCD actually maintains the image so your eyes don't have to worry about the constant motion from a CRT. Not the best explanation, but hopefully you get the idea.
I think CRTs are easier on the eyes than LCDs though. LCDs have a fluorescent backlight, and fluorescent lights ALWAYS have that annoying 60Hz flicker. It's noticible around your peripheral vision especially.
Cyclowizard has it.
Let's assume a 75 Hz refresh rate.
What physically happens for each pixel on a CRT is a stream of electrons is pointed at it, which causes phosphors just behind the glass to glow. These phosphors don't glow forever; much like the glow-in-the-dark toys you had as a kid, they're brightest just after they're charged, and they dim as time goes by. There are orders of magnitude differences, of course - Toys are designed to glow as long as possible (minutes), while the phosphors on the CRT are designed to glow for a very short time (tens of milliseconds).
On a CRT, it takes about 1/75th of a second to draw the whole screen. When the CRT is refreshing the bottom line of the screen, the phosphors on the top line are starting to get dim, because it's been awhile since they were charged by the electron beam. As long as the refresh rate is fast enough, your eyes integrate the brightness, and you don't consciously see the dim-bright-dim-bright cycles that each pixel is going through.
What physically happens on an LCD is different. Each pixel on the screen is controlled by a multiple Transistors (one for each color). When it's time to refresh a pixel, the individual transistors are turned on/off to adjust the brightness/color of the pixel, and they stay in that state until they are refreshed again. Thus, you don't have the same dim-bright-dim-bright cycle. That's why you can run an LCD at a 60 Hz refresh rate and not see any flashing, where doing that with a CRT generally gives a very obvious and annoying flash.
/frank
Let's assume a 75 Hz refresh rate.
What physically happens for each pixel on a CRT is a stream of electrons is pointed at it, which causes phosphors just behind the glass to glow. These phosphors don't glow forever; much like the glow-in-the-dark toys you had as a kid, they're brightest just after they're charged, and they dim as time goes by. There are orders of magnitude differences, of course - Toys are designed to glow as long as possible (minutes), while the phosphors on the CRT are designed to glow for a very short time (tens of milliseconds).
On a CRT, it takes about 1/75th of a second to draw the whole screen. When the CRT is refreshing the bottom line of the screen, the phosphors on the top line are starting to get dim, because it's been awhile since they were charged by the electron beam. As long as the refresh rate is fast enough, your eyes integrate the brightness, and you don't consciously see the dim-bright-dim-bright cycles that each pixel is going through.
What physically happens on an LCD is different. Each pixel on the screen is controlled by a multiple Transistors (one for each color). When it's time to refresh a pixel, the individual transistors are turned on/off to adjust the brightness/color of the pixel, and they stay in that state until they are refreshed again. Thus, you don't have the same dim-bright-dim-bright cycle. That's why you can run an LCD at a 60 Hz refresh rate and not see any flashing, where doing that with a CRT generally gives a very obvious and annoying flash.
/frank
Only transformer powered fluroescent lights flicker - and they flicker at 120 Hz (not 60 Hz). All LCD backlights, and most modern, good quality, fluorescent strip-lighting/compact fluorescent lamps are inverter powered. Inverter powered fluorescents do not flicker.
To be HT, those two statements aren't quite right. First off, LCDs are constantly refreshing -- as state above, the advantage they have over CRTs is that there isn't an off state between refreshes.
Secondly, the response rate is how long it takes for a pixel to go from one state to another (the ISO standard being for black to white). This is independent of how often it checks for pixel updates. Though the two combine to affect image quality, each one has a different effect on image performance.
If an LCD is driven at a refresh rate of 60Hz, then it checks for pixel updates 60 times a second (or every 16.67 ms). If the response rate of that pixel is fast enough to complete the update in that time frame, you'll see it completely rendered. If you're at a bad point in the response curve, say at some grey-grey point where it only has a response time of 34ms, that pixel may only be half way through switching before being told to switch to a different state. In that case, you'll only see the change half rendered before the next frame.
Oh, they flicker; mine does at least, but maybe it's just crappy.... (1920x1200 WUXGA) ?? How do you find out what kind of screens are in a laptop (Sager 3790) ?
Are you sure? My 21" Cornerstone CRT could do up to 120hz at low resolutions, and 100hz at most, and 85hz at 1600x1200, and then I think 75hz at 1836x1492 or whatever the highest res is.
BTW, since LCDs don't have a physical refresh, couldn't the whole "screen refresh" thing be done away with and graphics could just be updated as they change? Like no reason to use vsync, just draw the parts of the frame as they change. I think I've heard that the nintendo ds does something like this.
That explains why I find the light eminating from my LCD to be a bit hard on the eyes.
I'm not sure if mine does(besides, it could be internal), but I have a hyundai L90D+.
i've got a camera phone, and if i take a photo of a crt, then you dont get the whole screen (some is black as it is flickering) however on my laptop the whole screen is on, as said above, no tyechnical stuff just a method of showing the difference between how the two put the image on the screen
Still I find myself have to squint more when using an LCD as they contrast ratio is still not good enough so I think for my use it gives the CRT a very large advantage.
Also on nellienelson's point if you watch TV and there is a monitor in the background you can see lines rolling up and down the screen showing the dim-bright cycle but not with LCD's in the background.
Also on nellienelson's point if you watch TV and there is a monitor in the background you can see lines rolling up and down the screen showing the dim-bright cycle but not with LCD's in the background.
no flicker then at all. the backlight stays on continuously u see. but then you'd only be able to see the screen change once a second tooTRENDING THREADS
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