What I do.... I run 2 x 450w Spider farmers.....

When I start them and they are under 2 weeks old, I keep the light dimmed down all the way.... The lights are hung about 3-4 feet from the tops of the grow medium.. The object is to let the plants "grow into the light".. as you slowly turn the dimmer up to 100% over a week or 2...

As they approach 2 weeks old, I start just bump it up a little notch, like 10%..

What you will notice if you have the lights on to bright, is that they will look like they are "puckering", IE: (I know this will sound weird but.. I always think of them as "clinching their butt cheeks together"... cause the look they have reminds me of someone doing just that...)

They just won't be vibrant.. They won't look like they WANT to grow, and will look like they are getting TOO much "goodness".

So then when that happens, I just turn them down 10%, until they start popping again, then I will turn it back up half way.. then the next day another "half way".

By the time I finish flowering though, the lights are about a foot away from the plants.