When to go HPS from CFl

I have 4 fem seedlings almost 2 weeks old. Im going to move them to their forever home in a few days, I have some nice root systems going and don't want to damage the growth if it gets to long. Anyway they are under CFLs now and will go to 400w HPS, I was never good at this part. When do I make the switch, how do I transition them, ie;how far from the seedlings do I hang the light when do u lower it more etc. Like I said Ive grown b4 but this was always the hardest part for me to figure out. Help appreciated

They would do fine under the HID but you will probably need to back the light off a little for a couple days to let them transition to the new and brighter light. You could probably start them off at 2 feet or so from the bulb (from canopy of plants to bulb) and then close the gap after a couple of days. The gap you chose will depend on coverage and temperatures.. but generally the closer the better for later in flowering... i like to keep my 400 about 14" away from the canopy until week 4 of flowering and then probably about 8-10" depending on temps. you should be able to cover a 2'x3' very well during late flower with the 400 but if you have a 2x4 you might want to supplement light a little.

As for transplanting and transitioning. If I were you i would give them a short veg (4-6 weeks). Xplant into final containers. 2 days later (3rd day) put them under 6 hour HID 18 hours CFL. 4th day put them under 10 hours HID 14 hours CFL. 5th day put them under 12 hours HID. I like to supplement my 400w with about 100 watts of Cree White household LED 5000k a19 standard bulbs. I'm finding that 6-8 plants in 3 or 5 gallon containers would be the best route for the 400w. LST'd mostly with about 4 week veg.

Buy one of these to run while in veg http://www.thehydrosource.com/lighting/lamps/philips-mh-conversion-lamp-400w.html then switch over to your HPS bulb once you go into bloom.