Since I do not grow under lights, I will leave your main question to someone who does. That said, orchids, like all plants, need a rest period and a growth period. Light for day and dark for night. I *think* there are several factors to consider. How close is the light to the plant? Is the plant blooming size or seedling? What type of orchid plants are you growing under the light? For instance a phal will require much less light than a cattleya, etc...
I look forward to the scientific answer to your question. LOL.