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What Font Color Is Best For Eyes?
juraj writes "What font color and what background is best for the eyes, when you work for a long time? I have found various contradictory recommendations and I wonder if you know about any medical studies on this topic."
Brightness is the best control for eye strain. I usually lower the brightness to it's minimum and adjust the contrast accordingly. Less light lowers the strain to me.
Fly me to the moon Let me sing among those stars Let me see what spring is like On jupiter and mars
Like here.
Vivin Suresh Paliath
http://vivin.net
I like
There are so many variables to this.
- What medium are we referring to? CRT monitor, LCD monitor, printed matt page, Hi-gloss paper?
- How much ambient light is there?
- What type of ambient light is there? Incandescent, fluorescent, halogen...?
- What is 'a long time'?
- Who are we talking about? A 7 year old child, a 30 year old office worker, a 50 year old proof reader...?
Answer those questions and we won't all be shooting in the dark.The Mothership
Ok, that post was for fun.
For my shells, that I stare at for hours, I use:
green on black
yellow on black
white on black
It's usually green on black. I use yellow on black for special shells (like when I'm using a lot of shells with cssh). Putty defaults to white on black, so when I'm stuck in Windows land, that's it.
Any shells that default to black on white, I switch immediately. It's not so bad in a web browser, but there's something about a shell and typing in it that hurts my eyes. It could be that I'm concentrating that much more on the text on the screen, since it's usually fast data. Like, tail logs on a busy server, or run top with a refresh of 1 or 0. I catch details that other people don't even notice on their machines.
Serious? Seriousness is well above my pay grade.
Black is, of course, easy on the eyes, and Red does not effect your night vision, so I imagine this is the best combination. I have tried it, and I really like it.
I'm using Zenburn-like themes for quite sometime now and I find it pleasant to look at. (on the screen and not on paper, I just apply another theme if I want to print preview it)
http://slinky.imukuppi.org/zenburn/
http://en.wikipedia.org/wiki/Zenburn
The human eye is naturally lazy, and likes to look at things that do not cause it to send strong signals. To that end, a black background is essential for "easy on the eyes" formatting. From there, pretty much any light colour can be use for the text.
When I was in uni, I used to buy special black paper "visual arts diaries" and write my class notes using a gold, silver, bronze, or plain white ink pen. This had the effect of making my pretty poor handwriting easier to read for most people, and also reducing the effects of my dyslexia; I would make less errors like inverting a series of numbers as I wrote them down and the like.
For different working environment, e.g. with different "general background" color/brightness, you may need different color combination.
Well, nothing could prevent the eyes' fatigue if you keep on looking at the screen too long.
Colorless green Cthulhu waits dreaming furiously.
Nah...Bsckground: FF00FF Text: 7FFF00. Blink helps, too.
Some mornings it's hardly worth chewing through the restraints to get out of bed.
...because none of us have RTFA - as there isn't one.
I have found various contradictory recommendations...Err, that's nice. Where's the links?
The Mothership
I'll chime in as a physician.
:p
I always wondered in medical school what causes eyestrain -- your mom probably told you "don't read in poor light," but since the photons are easily sufficient to give an image on your retina, this didn't make sense to me.
It turns out that your eye muscles have a difficult time obtaining a rapid and precise focus with poor light, which gives less contrasts on the edges that are detected for sharp focus. In low light conditions, the eye muscles are rapidly focusing back and forth, and these micro-contractions can fatigue them similar to the other large muscles of your body. As an analogy, imagine walking on level ground versus on a balance beam. You are constantly contracting different adjustment muscles to walk on a balance beam, using more energy and promoting fatigue.
So, in answer to your question, you would want a high-contrast color scheme to make it easy for your eyes to focus on the letters. "Duh," I hear you say.
Next, I would recommend minimizing the difference in brightness between your monitor and the outside environment and its background. That is, in a dark office have a dark monitor, and in a bright office, a bright one. Why? Well, same reason -- your eye muscles have to dilate your pupil every time you look away from a bright monitor to a dark monitor. More contractions / adjustments -> more fatigue. Not only that, but the high brightness contrast will give ineffective normalization of light across the eye receptors and could cause headache.
Regarding your study question -- difficult to fund, and difficult to accomplish. I guess you would have to divide several hundred office workers, and try to have them work the same hours under same conditions with different fonts, and then ask a subjective question regarding symptoms. It could be done, but I am not sure of any well-performed efforts that have addressed this question.
In summary, I would just choose contrasting colors that you like or find subjectively pleasing, and then keep the brightness on your monitor appropriate for ambient lighting. Also, don't forget to focus on the numerous other ergonomic factors on your workstation. I see a *lot* of people with bad backs from the workplace, but there are a lot of 80 year old secretaries that are not blind.
Cue the contempt for expertise from the anti-intellectual crowd now.
Slashdotter, ID #101. UIDs are in binary, right?
There is no best set of "colors" for foreground/background, as evidenced by conflicting studies which tried to determine what that set was. Rather, what's important is contrast between the colors so that you can easily distinguish what you're seeing. So long as you maintain contrast, the choice of the specific colors is entirely subjective and up to you.
ColorBrewer http://www.colorbrewer.org/ has some of the answers. It will tell you about how well human eyes will be able to discern a colour scheme on various devices. It won't say much about the effect of staring at a particular colour scheme for hours.
I loved my 21" Eizo greyscale monitor. As a monochrome monitor, it had no colour gun registration issues and the text was razor sharp. It also supported 1600 x 1200 at a time when most people aspired to own a 1024 x 768 17" CRT. That is, the design and quality of the output device is also important for long term eye friendliness.
"Everything is adjustable, provided you have the right tools"
Call me old, but I've always preferred Grey lettering on a Navy background ala Word Perfect 5.1. At least when working on documents where graphics and colors are unimportant. I still keep Word configured that way to today. People accustomed to Black on White think I'm weird(er) for using it that way.
Or when I'm using a terminal, I usually setup a Green on Black color scheme, but Amber text would also be nostalgic. Even a shade of Grey on Black for an alternate nostalgia. SunOS was Black on Grey
My question(s) to you, what are you working on? Is it code? In an IDE or xterm? Do you have multi-color themes, like in an IDE? Or graphic design with lots of colors at once, in which a medium grey is usually standard? Working in a brightly lit, fluorescent bulb cubicle, an office with natural light, a basement with incandescent lights, or a dark room lit only by the neon/led/ccd bulbs of your case mods? These variables could effect your decision as much as anything else.
I think the best way for you to figure it out 'scientifically' is to come up with 5-10 combinations, try them each day at work for 1-2 weeks, and record your thoughts in a journal every hour or so. "Is this comfortable to look at? How's my eye strain? Can I reliably read what I'm doing? etc." Then pick your 2 favorites and try them each for a week straight, again making notes. Then decide on one. You can find what works for you over the long hours. I'm certain that my preference is different from yours. Obviously, you'll need to pick colors with higher contrast to each other, as Lime Green text on a Lemon Yellow background would probably be a difficult setting to get much done in.
"The quality of life is determined by its activites."--Aristotle
Yellow, becuase your eye is built to see the light of the sun
This will evidently come as a surprise to you, but the light of the sun is WHITE. That's why we call it "white light".
I seriously I always thought, Word Perfect's old combination white on blue was the result of such sort of study, and was included in Word for several years.
I normally try to set my windows to either white (or gray) on blue (or black). I increase the bright of the foreground depending of how light is the background (i.e. if I use light blue for background, I put white as foreground, but I use gray if the background is dark blue or black, the reason to pick each, depends on the flexibility of the editor for modifying colors when they have sintax highlight).
For xterms,
green on black
black on wheat
white on navy
cyan on black
orange on black
I use white on navy for emacs.
Wansu, th' chinese sailor
Well, it's better than this.
If you disagree with me on social issues, then it's pretty clear that you are a narrow-minded bigot.
I find that the contrast ratio of pure white on pure black is still too high, I favor white on grey rather like the way slashdot's "Reply to This" button looks. However having seen a friend's Kindle which uses reflected light, I find that the tradition black text on white background to be the most comfortable. I look forward to the day when there are full color, 60 FPS, reflected light monitors.
We are all just people.
indeed. it's insane how many CRT monitors are still operating at 60Hz when almost ALL of the hardware being used today is capable of higher rates.
For some of us with sensitive vision, looking at a 60Hz screen is like reading text written on a strobe light. Even if it doesn't subjectively bother you, it does cause increased eye strain. Apparently even OSHA cautions against 60Hz.
A good document on this issue ( show it to your librarian, IT pro, or whoever has locked you out of the control panel) is available here: http://www.nhpa.org/docs/ComputerMonitorFlicker.doc
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You are on the right track but there is more. Yes, higher contrast is better than lower contrast. But how this works with color is complicated.
One big issue is that the eye is not perfect optically. It cannot focus all colors at the same focal plane. Just how well it does varies by individual and the optical conditions of their eyes, and the quality of corrective lenses (which usually make it worse with respect to the ability to simultaneously focus all colors).
An important factor to consider here is which color or colors the difference is at the edge being focused on. For example in the "hot dog" pattern that has been mentioned in a reply here, the difference is actually in green. If the red level of the yellow part is exactly the same as the level of the pure red part, then all the difference is in green and this is an issue of green contrast. Yellow on red like this is essentially the same as green on black ... except that the extra red light with yellow on red causes the iris to close down more than the darker green on black would.
I find blue to be the worst to focus with. That may be because my sources of blue light are not sufficiently narrow band in the spectrum. Being spread out over the spectrum, it basically comes in fuzzy. Blue is also lower in contrast.
Green (be it green on black or yellow on red or even cyan on blue) is better.
Red seems to be the best in terms of focusing a sharp defining edge. You get red contrast with red on black or yellow on green or magenta on blue.
Unfortunately, effective contrast goes down when extra light is added in other colors. So you have to find a balance trading off the sharpness of the edge vs. the contrast. I've found a good compromise in orange on dark green (the level of green in the orange is the same value as the green background). Think of the orange in a neon sign on the green felt of a pool table. Then when I need to highlight something, I shift over to pink on cyan ... basically add the same level of some blue to both the orange and the dark green.
A related issue is light quality when reading a book or newspaper. Usually we are stuck with black letters on white paper. The consideration is then what type of light. I find that incandescent light, or sunlight, works nearly best for me for long term reading. Fluorescent lighting is worse. Ironically, I find high pressure sodium vapor light is about as good as, and sometimes somewhat better than, incandescent light.
To understand this, look at the spectrum. Incandescent light has a fairly even level through all light wavelengths. This makes those black on white edges a bit fuzzy. But fluorescent light has two narrowband peaks at a red and green wavelength (the blue is broader). This can make the text edge sharper ... twice. The eye ends up with two contrast edges. I believe this increases the eyestrain by causing the focus to be constantly jumping in and out to alternate the focus on the two different edges. It's a very small adjustment, but it is there at least for me. With incandescent light, it just settles in the middle of the fuzzy range and doesn't change much. And this is affected by how much light there is, which dictates how small the iris becomes. Higher light levels with a smaller iris won't change the effect from fluorescent as much as for incandescent, since with fluorescent the two contrast edges are already rather sharp due to the two narrowband spectral peaks. But for incandescent, the high light level helps (up to the point that intensity is too stressful).
This is why I believe we still need to keep some incandescent lighting around for reading and other close/fine work for long periods of time. I get a headache when working on things I need to look at closely when doing so under fluorescent light. The onset is about 25 to 45 minutes. I don't get the headaches under incandescent. And I have verified that the flicker is not the cause. White LEDs
now we need to go OSS in diesel cars
Yellow on Dark Blue. Especially for terminals and editors.
Legge, G.E. (2007). Psychophysics of Reading in Normal and Low Vision . Mahwah , NJ & London : Lawrence Erlbaum Associates. ISBN 0-8058-4328-0
http://vision.psych.umn.edu/groups/gellab/Categories.htm
http://www.lighthouse.org/accessibility/ for accessibility issues
There is quite a bit of literature on this question. However, badly crafted studies often turn out to be measuring preference not performance. You won't find badly crafted studies in the work of Legge, those who cite him, and those who publish in the same venues.
I usually use a dark grey on a medium or dark grey. Maybe something like #222222 on #777777. Enough contrast to read easily, easy on the eyes, and easy to focus on something else quickly.
White on black makes my eyes bleed, especially when trying to refocus quickly off-screen.
"He may be mad, but there's method in his madness. [...] It's what drives men mad, being methodical." G.K.Chesterton
The fonts in mac Leopard have gone from being pure shades of grey or pigment to polychomatic blends. Your eye reads them as a single color but the blend has a much less jagged appearance.
You can see an example here
Standing across the room and looking at the blow ups on that page I linked to two things are apparent. 1) you can't see the colors and 2) the color one looks more uniform (look at the upper part of the C) and more bold (look at the leg and curve of the R).
My guess is this. You can have more bold if you use colors because if two letters are adjacent in grey then a dark grey bold would bleed together but on these letters red is on the left and blue on the right so dark red and dark blue still have a contrast.
In the eye the ganglia are set up to sharpen edges of contrasting regions. So my guess is that this principle works for the cones as well as the rods meaning that the contrast between the red and blue separation is enhanced even if they have the same grey level.
Some drink at the fountain of knowledge. Others just gargle.
I was under the impression that there were two leading models of human color vision: opponent-process and trichromatic. Trichromatic stipulates that the there are three types of cones that register light at three different wavelengths corresponding to red, green, and blue. This theory is pretty well-supported in general. However, this theory does nothing to predict or explain afterimages (i.e. seeing a blob of purple in the shape of a bright [yellow] light after looking away from it, or seeing blue when looking away from a yellow image after staring at it for a long period of time). That's where opponent-process theory comes in. It claims that there are three types of cones specialized to receive "channels": Black/White, Red/Green, and Blue/Yellow. I don't really have anything to add as far as which color scheme minimizes eye strain, but thought I'd chip in on color vision in general.
...In fact, I still use yellow text on blue background for my IDEs ;-)
Yeah. That's also why unless you are colorblind, light yellow on a very dark blue will probably be about as readable as it gets because it has both luma contrast (difference in rod response) and chroma contrast (the yellow hits the red and green cones hard with just a little on the blue cones, the blue hits the blue cones and barely registers on the others). Even if you're colorblind, the huge difference in contrast should be sufficient to make it reasonably readable.
The absolute worst, IMHO, is white on medium green... you know... road sign colors. Unreadable until you get right up to the things, by which time you end up cutting off the guy in the next lane to slam your car into the exit lane that should have been marked 200 feet earlier.... :-D
Check out my sci-fi/humor trilogy at PatriotsBooks.
The retina doesn't get tired... it doesn't move.
The rest of the eye does as it tries to focus and refocus on a dark-but-not-dark environment, and the iris goes between contracting and expanding because it can't get a read whether it should be letting in more light because the background is too dark or contracting because the letters glow too bright, and the part of the brain running the ocular show will often make its displeasure felt in the form of splitting headaches.
For similar reasons, white text on a black background, while not as bad, isn't exactly good. This is why legal pads are pale yellow, and ledgers are pale green. Contrast is good, but too much contrast hurts.
I'm also used to green on black. And green is better than yellow or white on CRT monitors which have convergence problems, because you don't have red and blue that need to converge to green. It's probably better even on LCD monitors when you need small fonts. Also, out of the three primary colors, green appears the brightest (human eye perceiving).
Anyway, I seem to be very confortable with black on white used by web browsers if no convergence problems exist (no old CRT).
I know a lot of geeks like dark working environments. However, it is well established that this is bad for your eyes in the longer run (especially if you also need to read printed documents in the same environment, even occasionally!). When we still had CRTs, there was a really good reason for working in the dark - the curved screen meant that you'd get a specular highlight somewhere on your screen as soon as you switched on a light. That problem simply doesn't exist for LCD panels (and modern flat CRTs): you can always position those to NOT see a specular reflection from where you sit.
So: switch on your office lights, play around with the positioning of screen and lights until you don't see specularities, and then switch to dark on light background. Your eyes will thank you for it!
Actually, green on black is reported as the only combination that leads to permanent damage of color perception. It might not be too big a deal, but prolonged exposure is reported to make white fences in the distance look pink. This happens when the spatial frequency of the fence posts match that of the vertical strokes in the letters on your screen, as you normally see them.
Mid-white on black, e.g. #C0C0C0 on #000000 is surely the safest combination. First, you're not staring at a lightbulb for 8 hours a day. I really hate white backgrounds. It's only natural for the background to be black; if we're used to the white one it's because of retards who like to think of computers as paper (this is why I say using a computer, like any complex industrial machinery, should require a licence). Second, it has the most contrast for the lowest possibly light intensity, as you use your three light sensors more or less equally, not just one as in the case of green on black.
I was about to say 13256278887989457651018865901401704640, but it appears this number is private property.
Sub-pixel antialiasing might look sharper, but it'll always feel a bit out of place. I don't think it's easier to read. If you want bolder fonts, make them bolder, it's just that simple. If anything, sub-pixel precision is going to make them thinner. And not that it's an iFeature for iDigital iStylists only; FreeType and even Windows also support that.
Most font designers enjoy looking at bug legs on a screen, but I don't, so my fonts are personal modifications of popular fonts to make them bolder. (And yes, OMG, I have modified them which may be a violation of font designers' licenses! Fuck them!)
I was about to say 13256278887989457651018865901401704640, but it appears this number is private property.
Bullshit.
Double bullshit.
First, what is more tiring, some glow, when most of the retina remains inactive picking 'dark', or a full blast from a CRT tube against your eyes?
There are these who prefer bright background with dark letters over the opposite, but I assure you you'll find few of these amongst CRT screen users, and the choice of white on black for office applications was to make it all resemble paper, the old known metaphor for 'surface for writing'. Not because it's easier on eyes.
Then - did you ever use a monochrome monitor? Do you maybe remember why it took so long to get them replaced with color, even when color monitors were getting cheaper? It's because monochromatic monitors - green and amber especially, had far superior sharpness and contrast. I DID use them quite a bit, and I use one to this day, for long, long reading where normal screen would make my eyes water. It still beats LCD in means of eye comfort (black is REALLY black, as dark as the room, not backlight filtered through dimmed liquid crystal, and the brightness is widely tunable, so I can make the pixels just bright enough to be VERY visible without hurting my eyes.
Cost aside, green monitors give the sweetest reading experience out there.
45 5F E1 04 22 CA 29 C4 93 3F 95 05 2B 79 2A B2
But sure, if you use a dim green on black theme and for some reason a black-on-white application window pops up, it will burn right through your retina. Sai-aku!
A World in a Grain of Sand / Heaven in a Wild Flower,
Infinity in the Palm of your Hand / And Eternity in an Hour.
I'm amazed no one here actually sees this guy's point (yeah, yeah, I know - it's under his hat - ha ha ha - we're all amused). Attributing the human eye's color vision characteristics to survival of the fittest selections along with explanations is nothing but speculation.
It assumes that the vision spectrum capable is unbiased across all frequencies and selectable. It assumes that the selection conditions favorable to our particular spectrum were in place long enough to set them to this level. And that the eye hasn't changed since those conditions changed. And, finally, it implies that every property of our biology has to somehow be explained in Darwinistic terms.
Imagine if cats had infrared vision. Then, obviously, its because that was a characteristic that helped them hunt at night. But what about the fact that cats don't have infrared vision? Do we then say that natural selection screwed up? Oh - no - of course not. Its because that trait was never amongst the selectable options, darn the luck.
Now, before some zealot goes all Spaghetti Monster on me, I'm not arguing for ID or disputing evolution. I'm just pointing out that everything doesn't have to be forced into some universal theory. Maybe our eyes are the way they are just because they are. Nothing more. Stating anything else is purely speculative and should be phrased as such.
Honestly, what a load of hogwash.
... Black on White hurts more - I have a *MUCH* lower tolerance working with an IDE with a white paper colour than a black one. Of course, being a proper programmer, I use vi from a shell :)
:)
Green-on-black is perhaps the nicest thing to my eyes ever, though I am partial to Amber-on-black.
White on black hurts after a while
Yes I actually used serial terminals for years, usually in the higher column mode - just because I could read more
I kinda miss hacking on the old CP/M boxes from HP, and 68K unix boxes, not to mention AS/400s with their page-mode displays - boy that came in use when "the web" came out. Heh.
Red, being the longest wavelength of visible light (that lines up with a color receptor), carries farther especially in foggy, snowy, rainy, or other inclement conditions. This is why stop lights, stop signs, and tail lights are all red.
Blue, being the shortest wavelength of visible light (that lines up with a color receptor), is seen more vividly and in greater detail than other colors. "Ultra white" paper is actually tinted blue because of this, and many whitening laundry soaps are reactive on ultraviolet (which tickles the blue receptors without being visibly blue).
If you use a color calibration sensor, such as professional printers use, you will find that paper which is truly white in the scientific sense (equal strength responsiveness across the spectrum) seems kind of yellowish and bland compared to this ultra white stuff with it's big blue and ultraviolet spike.
I think this is why police lights are red and blue, red to carry in inclement conditions, blue to get your attention.
Slay a dragon... over lunch!
It's worth noting that the Compiz offers a plugin called Color Filter, which enables you to convert your whole screen to green on black in real time (among other themes).
Slay a dragon... over lunch!
thanks for the cute history lesson, but besides the use of "green" for nostalgic purposes, the question is really about sustained use of dark on light or viceversa. And for that let us travel further back into history - to ask a more essential question. Why do we type on white (light) paper using dark ink? Because is better for our eyes, or cheaper/easier? Hmmm...i think the latter. Eyes are actually better suited to spot light among its absence, than dark among overall light. And tho we may be well suited to see silhouettes on light planes, we truly excel at focusing our attention at lit objects and ignoring a darkened plane. Since only those receptors that see light are activated, minor shifts in viewing angles, give fresh receptors a "peak" of that light...and only trigger nerve responses momentarily, while the rest remain at "rest". If the process of ancient writing had enabled as efficient "light on dark" surfaces as a computer display, i'm sure that its qualities vis a vis ATTENTION would have been preferred and utilized. So the resulting technology was not because of it being better, simply more practical.
Also, the question is about not contrast - consider this...could you type for even a fraction of the usual time on a green display with black text? or amber display? Clearly the contrast ratio is the same as in the terminals you poo poo. If you really consider this point, and apply it to the argument you will come to the realization that we are more tolerant to faint light for the target (type) if the background is sufficiently dark (low contrast), and less tolerant to how bright the target has to be before we loose our target - if our target is a shadow (high contrast). What does the difference in contrast requirements tell us? Which scenario makes best use of our hardware (eyes). Because in dark-on-light our brain has to work in reverse - and register non-electrical triggers to spot the target, it needs more info to get a clearer picture, that simply processing "most active" triggers.
Of course it may be negligible to the optic nerve and cerebral cortex in the very short term, but - in the over all scheme - when it comes to attention, we tend light up our targets, so they stand out, not shade them..."well you can't control shadows as easily so its not practical" - you may say...well true, that's why our eyes developed to spot stand-outs and not the reverse! So exploit the way nature evolved our eyes to excell. Shine the target (type), and darken the non-target (background)...and in computers, that is now really possible and practical, if in the paper world that still isn't.
I'm red/green colorblind...
I noticed this recently when whiteboarding at work: I can see the bright yellow marker on the whiteboard clearly as can be (it really stands out) but my co-workers can barely see it unless they're within a few feet and even then, they're squinting. I can read it from across the room.
I was trying to figure out why this was and had no idea. Any thoughts?
I should also mention that any CRT with a refresh below 72 Hz gives me eyestrain within minutes, provided I can avoid watching the beam scan the screen (especially noticeable at 60Hz on any CRT).
The cesspool just got a check and balance.
Anyway, I seem to be very confortable with black on white used by web browsers if no convergence problems exist (no old CRT). In fact, given a good LCD monitor, black on white should be the best.
cleartype (or whatever subpixel rendering is named in your platform) is very good for providing nice easy to read letters. Full color works better with that rendering, so black on white whould be the best. Contrast should be high, and brightness should be adjusted to the lighting of the room. More light, more brightness.
The more it can look like paper, the better. Paper works great.
Readability and eyestrain are always at odds with each other. For readability purposes you want very high contrast between your foreground (text) and background colors. Obviously, white-on-black or black-on-white are the best choices for readability. The problem is over long periods of time high contrast viewing creates eye strain. This is why legal pads are yellow, for instance. The slightly lower contrast between a yellow background and a dark foreground reduces, but does not eliminate eye strain. The problem recurs at the other end of the spectrum if you have too low a contrast between your foreground and background. Your eyes strain to read the text and it makes things harder to read, period.
As far as colors go, the bottom line depends on the individual. We all see things a little differently, literally! Our visual acuity and duration to eye strain are metrics that do not necessarily apply to everyone and you really have to experiment to find out what contrast level works best for you.
The font issue is a little more defined. Proportional serif fonts (Times, Garamond, etc.) are good for print applications and are the most commonly used in printed publications. Proportional sans-serif fonts (Verdana, Arial, etc.) are best read on computer screens because of the dithering that often occurs to serif fonts. They are also easier to read on computer screens because the characters are more easily recognizable in the simpler, sans-serif form.
That's about all I can share on the subject. There are some well established guidelines, but because every human being is a little different there aren't any real hard and fast rules.