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) (EDIT 2015-03-02 This feature has been modified such that all themes are dark-on-light)
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?