Consider a couple of very small, high "windows" on the walls with best light exposure. Typically this type of celestory [upper] window just under the roof eaves is too small to be an entry point, too high to allow passersby to look in, easier to install without creating leak potential than skylights, and do not interfere with other uses of roof real estate - like solar or water collection. Even putting in a couple small rows of glass blocks will do the trick.