Do LCD monitors affect vision?

By AudioDope
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bdpmax

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A major difference between CRTs and LCDs is that LCDs don't flicker like CRTs do.  CRTs flicker 120 times per second (in north america, 100 times per second in the uk) due to the AC power cycle.  It's faster than our eyes can see, although if you record a CRT on video camera you'll see lines through it due to the flickering.  This doesn't happen on LCDs, as it's light is provided by DC power instead of an AC power.  As a result they are easier on your eyes.

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Flickering has nothing to do with the AC Frequency. They are resulted from the refresh rate. In fact the internal circuitry of a CRT converts AC current to DC.

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Fog Dogg

Posted
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LCD has a few advantages over CRT but if you stare at the screen 1-2 hrs at a time, you're going to cause some harm to your eye. You need take a break every 20 - 30 mins whether you have LCD or crt

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Really, I stare at my old cruddy CRT usually for more then 1-2 hours at a time; what harm can come from staring at an object for a few hours?

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Sticktron

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A major difference between CRTs and LCDs is that LCDs don't flicker like CRTs do.  CRTs flicker 120 times per second (in north america, 100 times per second in the uk) due to the AC power cycle.  It's faster than our eyes can see, although if you record a CRT on video camera you'll see lines through it due to the flickering.  This doesn't happen on LCDs, as it's light is provided by DC power instead of an AC power.  As a result they are easier on your eyes.

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Heh.. close, but wrong. Monitors do not flicker because of the type of electrical current they take. They flicker because that's the way they were designed to draw images. And the AC power cycle in North America is 60 cycles per second, not 120--It's 120 VOLTS.

A CRT fires an electron beam at a grid of phosphors, starting at the top-left of the screen, going left-to-right, until it hits the bottom. The number of times the CRT can "re-paint" the screen in a second is called it's REFRESH RATE. The NTSC standard for televisions is to re-draw the screen 60 times per second, partly because that's fast enough to make static images look like they're actually moving, but mostly because electrical current in North America is supplied at the rate of 60Hz, so it was the logical choice to use when they invented TV.

The higher the refresh rate of a CRT display, the more fluid the image it displays, the less noticeable flicker due to the constant re-drawing, and the less strain on your eyes. You should set your refresh rate to the highest rate your monitor can support for each resolution without over-stressing it. If you use your monitor at it's threshold (making it redraw as fast as it can), it will slightly blur the image and shorthen it's lifespan. So if your monitor can support 120Hz at 800x600, then feel free to use 100Hz. If it can support 90Hz at 1280x960, then try 85Hz. Typically, you should aim for 75Hz or higher. 85Hz is a great point to aim for.

The reason LCDs don't "flicker", per se, is because they use a different technique than CRTs to display an image. LCDs don't heat up phosphors, instead they use two thin polarizing films with a layer of "liquid crystals" in between. The screen is broken up into a grid of tiny pixels with red/blue/green filters above them. A light shines continuously at the screen, and tiny transistors control the alignment of the liquid crystals in order to let light through or not.

LCDs don't flicker, because the images are always on the screen. They use a 60Hz refresh rate to simplify the electronics (ie. update once per cycle of electric input). HOWEVER you DO still have to take into account the response time of the particular LCD screen and it's effect on the update speed. This is similar to refresh rate, but has no effect on flicker because, again, the LCD screen is always on, no matter the refresh rate. Response time is important for quick-moving images, like in games, because although the electronics producing the display are using power at 60Hz, it cannot change the alignment of the crystals--thus changing the color of the output--faster than it's response time. 25ms per update = 40 updates per second, which is too slow for playing games. 16ms and 12ms response times better suited for that task.

Grand Master

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REMEMBER if you stare at brick wall from same distance as you monitor and for the same period of time it will be bad for the eyes. Radiation and flickering are some concerns - but your eyes need movement too. Look at far distance once in a while for them to refocus.

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za3zoo3

Posted
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thx Sticktron very good acknowledge :)

but i have 2 q:

1- its matter if you change the refresh rate for LCD through windows properties as its use tiny transistors to control the pixels ?

2- i love LCDs screen cause they have wonderful color, at least you can distinguish between the CRT and LCD it looks like natural colour and some people consider this as a good advantage over CRT

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KHaKi-

Posted
Posted (edited)
Heavy computer use is tied to Glaucoma...

Also, when you stare at a monitor you tend to blink less because of refresh rates and such, thus drying out your eyes, etc. That is also proven.

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Atleast I get to smoke more :laugh:

I use my LCD for about 6 hours everyday, except weekends where its about 12 hours straight since we have LAN Parties every weekend.. :wacko:

Edited by Khaki72nd
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AudioDope

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Same here, 60hz kills my eyes and gives me a massive headache.

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wow u know alot about this stuff, anyways, i changed it to 70hz, iwas at 60 in the beginning :| can u believe it? i was used to it from so long anyways, now im on 70 Hz...on 800x600 res...i also heard about the color quality? i heard u shoulden't have it on 32 bit if u dont play games, etc and it hurts ur eyes? does it?

edit: i gotta get a lcd now ;( any recommendations for a cheap one? i have only about $300 :(]

Grand Master

Raa

Posted
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Hi all

So.... its about LCD vs CRT eh? heh heh, thats a fun topic :)

I love both, for different reasons.. I think my 21" Sony's better than a LCD screen lol

The refresh rate on a LCD screen does nothing - that i've ever noticed. Anyone feel free to correct this one, but i'm sure it has no effect (??)

The refresh on a CRT should be set as high as it can go without your monitor screwing up true - If you're going to tape it, I found that 75hz is the best rate for PAL users.. NTSC is different, so I couldn't tell you there.

(why tell you that? well uhhm.... taping drunken quake players is one excuse :D lol)

Also : If you're going to get an LCD - dont use it.

Seriously! *MANY* are rated between 10,000 -> 30,000 hours of use... Thats not a lot when you start to think about it.... I mean, I use my monitor a lot.... I've never noticed a CRT "Wearing out" in 3 years heh heh ;)

Anyway, my 20 cents worth!

Veteran

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and i cant say i've seen a tft ever wear out either. i mean by the time my tft does die i'll prob have another 2 of them sitting here and i dont even have a source of income atm.

Seriously I've been sitting here with a tft for 2 years now running 12 hrs a day and it's still as good as the day i got it - well bar 1 dead unnoticable pixel

And as for gaming - i've never once seen bluring in any fast moving games and this is a 25ms rated monitor

and yeh there so much easier on the eyes - i find it difficcult / distracting using machines with crt's these days - especially at school - it just really annoys me

Veteran

tagerd0g

Posted
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i thikn my eye sight is getting worse and worse, and i want it to stop..but i cant really avoid computers because i do all my work on them (hmwk, etc) and stuff..I dont have $400+ but i think i have around $300 so any decent lCd/crt monitors for that much in canada? [ont]

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if your eyesight is getting worse, then you need to see an eye doctor. if you have an underlying issue, then the doctor will help you on that.

search this site for some deals.

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MEMO.INC

Posted
Posted
A major difference between CRTs and LCDs is that LCDs don't flicker like CRTs do.  CRTs flicker 120 times per second (in north america, 100 times per second in the uk) due to the AC power cycle.  It's faster than our eyes can see, although if you record a CRT on video camera you'll see lines through it due to the flickering.  This doesn't happen on LCDs, as it's light is provided by DC power instead of an AC power.  As a result they are easier on your eyes.

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The "flickering" is not caused by the frequency of the Power source, Ity is caused because the electron gun doesn't paint 5the whole screen at one time, instead it goes pixel by pixel scanning the whole screen in some sort of "zig-zag" way, you can adjust the frequency of that "refresh" in WinXP in the Monitor settinfgs on advanced tab, the more the frequency the best. My CRT can run @ 1280*720 but it locks me at 60 hz, and when i am at 60hz i get headaches thats why i do 1024*768@85hz. so if you are getting headaches by using CRT, just cranck up the refresh rate or get a better one refresh-rate wise

Grand Master

+Random Stranger Subscriber¹

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And as for gaming - i've never once seen bluring in any fast moving games and

this is  a 25ms rated monitor

somehow i dont belive it. playing on a samsung 25ms lcd after my crt was horrible the first few minutes. all blurry. you do however adjust very quickly and dont seem to notice it anymore - which is what happend to you

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tkyoshi

Posted
Posted

Normally windows defaults to 60Hz for compatability with most types of monitors however i makes my eyes go all O_o just staring at it.

Most average people's computer systems i've used are set to 60Hz which drives me crazy, even computer labs at school are all set to 60Hz.

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