Not sure there is a definitive answer. I grow mostly Phals and Paphs under lights and have since 1989. As far as I can recall, I have never altered light with the seasons and the plants do just fine. I run lights about 16 hours a day and also have some natural light from a sliding glass door. I suppose it is possible some plants may be more finicky about the amount of light, but I don't know of any specifics in that regard.