Im unable to vote. None of these options seem appropriate. Light is just another nutrient. Granted, making light the limiting nutrient seems the most important factor in algae control to me, it is not alone in controlling algae. All of the options other than lighting spectrum seem like they would work for controlling algae under the right circumstances. IMO its all about creating a situation in which the plants are able to monopolize the available light. So, "none of the above".