Metal halide light is as close to sunlight as possible; I would move from sun to halide at full strength and leave it there... or turn it down gradually, if the bills are too high. Sorta like what the trainer told his jockey of Secretariat at Belmont.... "Take him to the front and keep him there; the horse that can beat him has not been born" I was/am a great lover of "Big Red"; after 40 years I still cannot watch the movie without crying.

I've used MH for citrus, I start the light 6 to 8 inches above the top of the tree on full strength, then move it down a little each night until the light is 2 or 3 inches above the tree. Normally I also put reflectors around the tree that I trying to light.