Is an LED monitor better for eyes than an LCD monitor?
EDIT: And if you are allergic to fluorescent light, is LED going to be better? I heard that LED doesn't uses fluorescent light.
there are two things which are casually referred to as "LED" monitor
OLED monitors - these are relatively small, as of the current moment, each pixel is lit by a small OLED, usually used on mobile devices only. there are desktop implementation (read: the sony OLED monitor which cost thousands of dollars). these looks better. they have great contrast ratio, good color rendition but are expensive & had a relatively short lifespan (due to the blue OLEDs - these had relatively low efficiency and die off early)
see http://en.wikipedia.org/wiki/Organic_LED#Disadvantages for details.
LED-backlight LCDs. there are still two kinds of these things on the market. The cheap kind is white-LED based. The color rendition is not yet on par with good CCFL backlights (e.g. iMac 27" vs dell U2711, the imac uses the white LED backlight and dell U2711 uses CCFL backlight but the dell had a larger gamut (color range)). the RGB LED backlight is very advanced and can give a very large gamut.
in general, looking at monitors does nothing to the health of your eyes, and more importantly, the contrast and brightness settings matters more than the nature of the lighting efficiency. In selecting monitor. First choose LCD panel (if you needed it - IPS panel vs TN panels vs VA panels) then choose backlight (colour range, power use).
To make everything easier to your eye, adjust the brightness of your monitor according to your ambient light level.
Ok, firstly there aren't any truely LED monitors. What you can buy nowadays is a LED backlight LCD monitor.
On that basis, I don't think there is any difference at all. LED backlight monitors do have a better contrast ratio, but I don't think that they're yet good enough to have a real difference to eyestrain.
As far as flicker goes, it depends on how the backlight driver works. When I was at a computer store several months ago (late 2010), I examined many of the LED-backlit LCD monitors, and found that almost all of them flickered noticeably when the brightness was turned down to a comfortable level, while my CCFL-backlit LCD has no flicker, even at minimum brightness.
You can easily test a monitor's flicker by waving your finger back and forth in front of the screen while showing a bright image, like solid white. If you see a smooth blur of an afterimage, it's not flickering; if you see lots of distinct after-images of your finger, it's flickering at a low rate and can cause eyestrain.
It's pathetic that LED backlight drivers don't set the flicker rate much higher so it's not visible, since LEDs impose virtually no constraints on the rate. But LED backlighting is still in its growing stages, so give it a few years.
It's easier on my eyes when I turn up the brightness on my 22" LED monitor to 100% in order to eliminate all the flicker and use polarized reading glass covers to knock down the brightness. LED monitors control brightness by causing a flickering effect. LEDs use very little current so to turn down voltage isn't an option. The slower the flicker the dimmer the screen because of longer off times in the flicker therefore 100% brightness has no flicker. The brightness was causing eye stain, but the flickering was causing eye strain and brain strain, so the combination of 100% brightness and sunglasses works best for me.
Current OLED monitors are tiny (as in mobile phone screens), so no - you'll probably get eye strain trying to see anything in a monitor that small ;-)
The general rule with monitors is that you should get a monitor that is large enough to display the resolution you want without the pixels being too small, and with a refresh frequency that you're comfortable with (I'm OK with 60Hz, but many people need a higher rate).
Monitors can be too bright for long term use. Monitor brightnesses are designed to look good on display in a brightly lit store etc, and of course people tend to see those brightness and contrast figures and assume bigger numbers are always better. Burning out your retina with your absurdly bright monitor is not a good thing, so make sure you adjust the brightness and contrast settings to be suitable for where you are working.
Using a TV as a monitor can be a bad idea because of the image processing that TVs tend to do, like sharpening, which can cause some discomfort with long periods of close-up viewing.
Beyond that, it's mostly common sense stuff - your monitor shouldn't be too close (causes focal-distance eye strain) or too far from your eyes, and you should take regular rests. And it's worthwhile investigating settings for default font sizes in your operating system, web browser etc.
LCD vs. CRT, plasma, etc... AFAIK it doesn't make a lot of difference.
Whether one can perceive flicker doesn't only depend on the flicker frequency. It also depends on the brightness difference between 'on' and 'off' and on the duty cycle, i.e. the fraction of the period the LED is 'on', and on the attenuation speed. LED luminiscence is like a block wave, whereas CCFL is like a sine wave. Furthermore the direct field of view of ones eyes (done with the 'cone' cells) are less sensitive than the surrounding field of view (with 'rods'). So, you may not consciously perceive flicker, but your eyes/brain still perceive it.
LED backlit screens indeed flicker at a higher frequenncy than the refresh rate. I tested this by filming a pencil swinging in front of the screen. The flicker frequency proved about 90 to 120Hz.
At highest brightness the duty cycle is 1: the LEDs are always 'on', never 'off'. Instead of wearing sunglasses, you can slide one or more pieces of window foil or car foil under the frame of your monitor. Such foils exist in many different degrees of light transmission.
There is, unfortunately, another effect playing a role. 'Edge-lit' monitors (most LED-backlit monitors) contain a plate with tiny raised bumps that reflect the light under an angle of 90 degrees. With lower quality monitors these bumps may yield 'hot spotting' (lighter areas), which looks like light scattered from a water surface at a small breeze (like a pond).
Full-lit monitors don't have these bumps, but they have a diffuser. If the diffuser doesn't exactly match with the matrix of LEDs, it may cause 'blooming', which looks something like light scattering through raindrops on the front pane of a car.
I wonder whether 'allergy' for CCFL exists. No doubt some CCFL users experienced problems, but that may also be due to low quality or other hardware causes. TL tubes, the ones used two illuminate rooms, indeed flicker visibly, but for most people only at a close distance (e.g. when used as a desk light). This is because the brightness difference of a TL is much much bigger than that of a CCFL tube, and because there is no diffuser screen in front of it (like with CCFL).
CCFL had another advantage, that of a completely matte screen. Very comfortable for the eyes. CCFL monitors haven't disappeared completely yet, but are hard to find. I sincerely hope CCFL will make a come back soon.