While working on my latest website, I started actually wondering if what I learned in grade school was true. I've been taught that programs like Word default to use a white background with black text because it's easier on the eyes than the old phosphorous displays which were always light-on-dark. However, I find more and more that it hurts much less for me to read light text on a dark background; my lenses feel like they're straining less, and irises can relax more due to the lower overall light level.
So is it true that dark-on-light is easier to read? Have we just been told this to make us believe that these programs are advanced or something like that? Was the change to dark-on-light made more to simulate ink-on-paper moreso than for visual comfort?
The science of readability is by no means new, and some of the best research comes from advertising works in the early 80s. This information is still relevant today.
First up is this quote from a paper titled “Improving the legibility of visual display units through contrast reversal”. In present time we think of contrast reversal meaning black-on-white, but remember this paper is from 1980 when VDUs (monitors) where green-on-black. This paper formed part of the research that drove the push for this to change to the screen formats we use today.
However, most studies have shown that dark characters on a light
background are superior to light characters on a dark background (when
the refresh rate is fairly high). For example, Bauer and Cavonius
(1980) found that participants were 26% more accurate in reading text
when they read it with dark characters on a light background.
Reference: Bauer, D., & Cavonius, C., R. (1980). Improving the
legibility of visual display units through contrast reversal. In E.
Grandjean, E. Vigliani (Eds.), Ergonomic Aspects of Visual Display
Terminals (pp. 137-142). London: Taylor & Francis
Ok, 26% improvement – but why?
People with astigmatism (aproximately 50% of the population) find it
harder to read white text on black than black text on white. Part of
this has to do with light levels: with a bright display (white
background) the iris closes a bit more, decreasing the effect of the
"deformed" lens; with a dark display (black background) the iris opens
to receive more light and the deformation of the lens creates a much
fuzzier focus at the eye.
Jason Harrison – Post Doctoral Fellow, Imager Lab Manager – Sensory
Perception and Interaction Research Group, University of British
The "fuzzing” effect that Jason refers to is known as halation.
It might feel strange pushing your primary design goals based on the vision impaired, but when 50% of the population of have this “impairment” it’s actually closer to being the norm than an impairment.
The web is rife with research on the topic, but I think these two quotes provide a succinct justification for why light text on a dark background is a bad idea.
I do hours and hours of editing and translating in front of a computer all day, and my experience is that for such text-heavy work, light text on a dark background (for me, either white or a very light green on a black background) leaves me less fatigued, noticing far less strain on the eyes. Doing such intensive, long editing and translating with dark text on a white background is like staring into a fluorescent light bulb all day. Of course, if you're just browsing around the Internet for briefer periods, it's enjoyable to see all the various design choices web besigners have made, and some of them are worthy of being called works of art, but for plain old drudgery, simple, retro light-on-dark seems superior to me.