I would say that if sunlight is causing algae, then its because ofthe nutrients in the tank, not the light itself. I once had a tank that recieved lots of sun in the morning. I had a 250w Iwaski bulb that was drowned out by the sun.
Aside from a bit more algae film on the glass, not many other problems.
My corals use to love it and they always seemd to expand even more. I would suppose tank size has something to do it also. Over heating in a smaller tank is easily possible from sunlight, so that must be watched.
Its also like putting 400w halides over a tank that been running on low lighting with no algae. If nutrient levels are high, they stay in check with lower lighting but increase the lighting and instant green.