You must have perfect eyes, then.
Generally speaking, black-on-white is easier to read than white-on-black. Theory behind that is simple: the more light comes in to your eye, the smaller the pupil, thus sharper image.
This is only true to a certain point, as neither extreme is particularly appropriate for long-term use. The trick is managing contrast in your color selection--high enough for readability, but not so high as to cause problems.
In the case of light-on-dark, it means not using solid black, because it causes bleeding. In the case of dark-on-light, it means not using very bright whites, because it causes eye strain unless brightness is considerably reduced.
The "more light" entering your eye theory you advance has more to do with ambient lighting than the properties of the display. If you are working in an appropriately-lit space, the color scheme of the monitor contents is relatively unimportant to pupil dilation, since ambient light is the largest component of total light in that case. On the other hand, the color scheme
is important to eye strain, caused by too-bright light sources, like massive fields of pure white on a monitor.
On the other hand, eye strain on light-on-dark color schemes is a factor only in rooms with far too little ambient light.
So, in conlcusion -generally- it is easier on the eye if black text is on white surface. The more light the better (for the eye).
These two statements are largely independent--the correlation you imply doesn't exist. More
total ambient light (to a point) is better for the eye;
less direct light (again to a point) is better for the eye. These are competing forces, and why books and emissive displays have different optimal values. Dark-on-light provides better responses in reflected light media; light-on-dark manages direct light source media better. Either one can be used in either kind of display/media, so long as it is properly executed. Extremes of either are a bad idea.
