Dimly lit room + brightly lit cube means that whenever your vision tracks outside of the cube it will have to adjust the opening of the iris. Doing this a lot will tire your eyes out. My interpretation of this is that we should try to have about the same light level across our work spaces and that this should be a mean between long term comfort and readability. I think most of us could probably benefit from larger font sizes as well which feel easier to read in lower light to me.