Which is easier on the eyes: dark-on-light or light-on-dark?

Question

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.

I've tested both on http://BHStudios.org/about and you can see the results of these tests by switching between "Dark" and "Light" themes under the "Modern" category in the dropdown in the sidebar. (This feature does not yet work in Internet Explorer)

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?

Answer 1

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 Columbia

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.