Just an FYI for HID people with digital ballasts. Don't dim your bulbs. They're meant to operate at a certain voltage/temperature and by dimming, you lose the full spectrum the bulb is capable of. You're better off raising your lights.
Also, just remember, seedlings in nature don't get the benefit of low light to start. They get blasted by the sun, wind, rain, cold just like everything else. While I think you should be gentle, at the same time if you coddle your plants too much, they won't be as tough IMO.
Personally, I harden them off by keeping my light 3 to 4 times higher than normal and drop the light gradually every day for a week. By the end of the week I'm at optimal height. Works for me anyway.