When you say "other one", I assume you mean that you're running a Metal Halide bulb now and you can switch to a High Pressure Sodium when you switch to flower. you're leaves are still pretty light green. I'd say it's a nitrogen deficiency but it's hard to tell from a pucture. Have you checked the PH of your soil or of the runoff water yet? I'd also say that you're ready to go into flower whenever you're comfortable with it. I like to have mine vigorously healthy before flipping but it's rarely past maybe 8 weeks with 5 or 6 weeks from seed being more common. Other people may prefer to do it differently, just my 2 cents.