why wouldn't a private office have natural light?
edit: longer answer - I work in Mountain View, where there is huge competition for buildings thanks to Google. Small companies get the leftovers, and beggers can't be choosers.
The the extreme example of this is seasonal depression, which is the reasons Scandinavian countries have very high rates of suicide.
But good scientific studies show most people are effected by lack of sunlight, and it impacts mood and alertness.
Windows in offices is an expensive problem to solve, but as sunlight frequency strip lighting is the same price as the yellow stuff normally seen in offices, I'm surprised we don't use it.