I have 5 plants growing in a 3X8 growroom with an exhaust fan in the ceiling and a fan pushing fresh air into the grow room. All of the plants are still seedlings only 5 days old. Right now I have each of them under there own set of two CFL bulbs. I have a 600W HPS light that is just waiting to get turned on but am not sure if it's too soon yet or not. When can I turn on the HPS and at what height should I set it at? I was going to mount it at the height that it was not too hot on my hand at the level of the plants. Thoughts?
Roughly 18 inches, potentially a couple of inches more or less depending on your exhaust set up. If it is encased in clase you can go closer maybe to around 10 inches, but if you just have it normal. stick with 18" You should switch to 12/12 at around 3-4 week mark.
For now you can stick with those CFLs or use the HPS, but keep the HPS backed off a good way from the sprouts. For a 600w I would start at about 3 feet away and lower a couple of inches a day, in another week or so you should have it at a good height. The right height might be around 18" but go by the back-of-the-hand test rather than any set number of inches. Best of all is to get a thermometer with a remote probe/sensor and mount it directly under the light at plant-top height, then use the temp readings as your guide.