All of these "algae will grow like crazy" replies are completely incorrect. Lighting is never the limiting factor in algae growth, dissolved nutrients are. NSL (natural sunlight) will not cause more algal growth than artificial light with the same given PAR (photosynthetically active radiation).
Natural sunlight is infinitely superior to artificial light, and I have a nano that gets direct sunlight from a large window. I have seen entire coral propagation greenhouses lit by nothing but natural sunlight, and believe me, they wouldn't use the sun if it wasn't the best option out there!
People often forget that there is huge, diverse ecosystem thriving in the ocean that has been around a lot longer than our species has, lit by the sun!