Refresh rates and eye strain?

[aaroncgi]

I'll be purchasing a new monitor to go with a G400 of some flavor in a month or two, and am curious how refresh rates affect image quality and eye strain. I see lots of articles saying how anything below 80 or 85 Hz horizontal refresh rate is torture on your eyes, but little explanation why!

For reference, I looked up the rates on my current 15" monitor, and the highest one I use is refreshing at 60Hz! Never noticed any problems looking at it for long periods of time, nor the ones at my work which are similar and I look at all day. Does the situation change when you go to a 19" ?

The monitor I plan on getting will do 85Hz refresh to 1024 x 768, 80Hz at 1280 x 1024, and 65Hz at 1600 x 1200. It's a shame there isn't somewhere you can go and actually see a decent selection of monitors, numbers don't really tell me much about how they look!

Aaron

[WarFlail]

I don't know what the scientific argument for a higher refresh rate would be, but I find that refresh rates below 75Hz are a little blurry. Low refresh rates also seem to affect the framerate of games, although I'm not sure if this is true or not - it just looks that way to me, especially in 1st person shooters when spinning around corners, etc.

I had my monitor set at the default 85Hz for well over a year before I discovered just recently that I can crank the sucker up. The optimum settings for my monitor seem to be as high as 160Hz on 640x480, 147Hz on 800x600, 117Hz on 1024x768, etc. Now I find everything looks just a fraction sharper and smoother than before.

I think the sharper the image, the less eye fatigue you suffer.

-=W=-

------------------
My system specs:
Intel Pentium III 650MHz
Asus P2B motherboard
128MB PC-100 SDRAM
Matrox G400 32MB SH @ 141/188/141MHz (no additional cooling), ParaKnowYa's driver pack v1.5 installed
Creative Sound Blaster Live! Value with latest drivers
Quantum Fireball ST 6.4GB & 4.3GB
I/O Magic 8X DVD-ROM (region-free)
Kenwood 42X TrueX CD-ROM
CTX PR711 17" Monitor, currently running 1024x768x32@117Hz
Microsoft Intellimouse with IntelliEye
Logitech SoundMan X1 speakers and subwoofer
Windows 98 (not SE)
3DMark2000 default benchmark score: 3024

[RAB]

The biggest problem with low refresh rates is flicker. That's the apparent pulsing of screen brightness that is very bothersome to some people (me included) and not bothersome to others. It is much more apparent when you look at your monitor out of the "corner of your eye". Look just to the side of your monitor, instead of straight at it, and see if the picture is flickering.

The problem is much worse when your room lighting is flourescent rather than incandesant (regular light bulbs). Most people will notice it at work more than at home for this reason. The flickering is caused by a wave phenomena called beats. Whenever two sources of light (or sound) are in close proximity to each other and are pulsing at frequencies very near each other there is a peak and a valley in the brightness of the two sources added together. It is mathematically the difference in frequency between the two sources.

In the case of flourescent lights and your monitor, both are running close to, but not exactly 60hz here in the U.S., you get a fluctuation in apparent brightness of your monitor of one to three hertz - the difference in their actual "refresh" frequencies. This is very apparent and very bothersome. If, however, your monitor is using an 85hz refresh rate, the difference or flicker rate, is about 25hz. This is not as detectable by the human eye which has a hard time distinguishing separate pictures at anything over about 16 times a second. This is also why a 75hz refresh is considered the absolute minimum (75-60=15hz).

The reason you get more apparent flickering with flouresent lights is because they turn off completely 60 times a second, just like your monitor. Their intensity therefore varies 100% between off and on. This makes the beat phenomena very appparent. Incandescent lights do not turn off completely since their filaments do not have time to cool between current cycles and therefore their light output never goes off. They do vary a small amount in brightness during each cycle, so there is still some flicker on your monitor even there.

I hope this explains why refresh rates are important. But also why it affects some people more than others.

RAB

[This message has been edited by RAB (edited 25 June 2000).]

[xortam]

Very good explanation RAB. I understood the minimal acceptable level was 72Hz, and that is what the VESA standards are speced for. Close enough. The most sensitive color to refresh rates is a solid grey. Set up a field of grey and watch the flickering as you lower the refresh rates. Eyes will fatigue over time and younger eyes can tolerate more abuse but it effects us all and the idea is to minimize the damage to maintain your eyesight for the long run.

[aaroncgi]

Thanks for the info everyone, very informative! I think my monitor choice will probably be good enough for me even though it doesn't have super high refresh rates. (getting a Samsung 955DF). The 0.20mm dot pitch and flat screen should help.

As for looking at a monitor out of the corner of my eyes, that doesn't work because I wear glasses. Thus looking at anything out of the corner of my eye makes it blurry. Like I said, I can't see any flicker at 60Hz, even at work, where all flourescent lighting is used. At home I don't have any lighting source on near the monitor, flourescent or otherwise.

In regards to lighting, halogen bulbs with a AC-DC transformer are on full time, correct? However it appears most of the torchiere type 300w dimmable halogens run off AC directly..

Aaron

[MadCat]

Its hard deciding on the refresh rate to run at mainly because the higher your refresh rate, the blurrier your picture is. I am extremely sensitive to flicker, and though I can stand 75Hz for a little while, I find 80Hz to be the optimal balance between image quality and flicker.

As for not noticing flicker, youre not alone. Many people I work with also dont notice.

For those of you with flicker sensitivity, Flat-Panel TFT screeens are the ultimate way to eliminate flicker (this can be a bad thing). I spend all day working on a laptop and when I use my monitor at home, even higher refresh rates seem flickery to my desensitized eyes for the first few minutes.

------------------
This Signature Space FOR SALE / RENT

[GBates31]

the higher the refresh rate, the less strain on your eyes. Use the tool that comes with PD to adjust your refresh rate to around 110. My monitors original rate is 85Hz but ive overclocked it to 119Hz.

[xortam]

There are limits to how high you should push your monitor ... check your manufacturer specs. Traditionally, one could permanently damage the monitor by overdriving. The first complaint from mine is that I'll start to hear a faint whine, which also can be fatiguing over time.

[MadCat]

And lets not forget,

Higher refersh rates = blurry picture.

Just try reading text at say 80hz vs 100hz at any higher resolution, youll notice the difference.

------------------
This Signature Space FOR SALE / RENT

[bongo]

completley personal decision imho, my eyes strain at HIGHER refresh rates because the blur on txt is too much...flicker is no big deal for me..I have my monitors at 60hz...but it is very important that you have a good card/monitor combo

------------------
"The path of excess leads to the temple of knowledge"

ABit BE6 II UDMA 66 w/ PentiumIII 500mhz
Matrox G400 DH 32 meg MAX
Maxtor 13gig UDMA66 7200 Seagate 9gig UDMA33 7200
SBlaster Live Mp3+ (with gold connectors and robot voice
Aureal Vortex SuperQuad2500
19" PF790 Viewsonic (superb flat screen)
19" Samsung 950p (amazing quality for the price)
Panasonic 7585 CD RW 32x8x4
Pioneer DVD 114 10x40x
USR V90 ISA everything modem
3COM ADSL HOME CONNECT WarpMODEM
One big case fan and standard retail CPU/HS cooling
MicroSofty Optical IntelliMouse Explorer (sheesh, who would have thought a mouse could make such a difference)
ACK 580 crdless k/b

[kjliew]

Sensitivity of one's eyes towards refresh rate can be different. Some people don't seem to be able to differentiate between 60Hz and 75Hz. I am not sure about you people out there, but for me, I am particular sensitive to refresh rates lower than 75Hz. And, my eyes tend to strain if I work for long hours in front of 60Hz screen, which I used to be in the early days. VESA official vision ergonimics recommendation is 85Hz.

Most 14" monitors are not capable of 75Hz at 800x600, but most 15" digital flat screen monitors do. Some good brands 15" can even do 85Hz at 800x600.
In my opinion, for 15" and below, 75Hz is good enough. For 17" and above, you'd better go with 85Hz or 100Hz, especially on real big monitors such as 19" and 21". The 75Hz on 21" monitor looks like 60Hz for me. I am working on 21" monitor at 1024x768 at 85Hz in office. This is barely enough for me, but this is the best I can get from my laptop external port. It doesn't look as comfortable as 1024x768 at 85Hz on a 17" monitor.

Next,
*higher refresh rate != blurry picture*

Most monitors have a set of factory recommended refresh rates. As long as you stay within that limits, there will be no picture degradation as you go for higher refresh rates. I have tried this on high-end Sony 19" and 21" monitors. The text looked as crisp as it is in 1280x1024 85Hz and 1280x1024 100Hz. It would be a different story if you try to force the poor 15" monitor into 800x600 100Hz. However, most monitors are capable of more than that. For eg. if the factory recommended highest refresh rates for 800x600 is 75Hz, in most cases the monitor can actually do somewhere in 83-85Hz. You will only get picture degradation if you use it at out-of-factory specs. Software like SciTech Display Doctor, Matrox Powerdesk, PowerStrip etc. allow you to do such things. If you use Linux, you should know that Xfree86 will give you even more video-timing tweaks. Having monitors operate at out-of-factory recommended refresh rates will shorten the lifespan of the monitor, and more seriously, may post some health hazards issues cause by EMF emission. All the health/emission ergonomics compliancies can be void with out-of-specs refresh rates.



[This message has been edited by kjliew (edited 29 June 2000).]