How Long to leave the lights on?

[Pokey49]

I have about 20 orchids in the northwest corner of my sun room which has windows on the north, east, west and two sky lights, but the light is low this time of year. we live in Oregon. I have decided to give them supplemental light during winter and have 5 grow lights shining on them starting today. I am still cogitating over which kind of bulb I should be using. Right now I have 5 50w incandescent grow lights going. Still researching if they of CFLs would be better, but my next questionis: how long to leave the lights on? My wife thinks I should turn them on mid day about noon and shut them off about 8pm. I was thinking to turn them on asbout 8am and off about 5-6pm? I have no idea how long these lights should be on and the best time of day to have them on. Any advice out there??

Paul