I've been growing kale, chard, tatsoi and Chinese cabbage in a greenhouse attached to my house during the last 4 winters. Spring and fall production id quite good, but during the darkest part of the winter the plants recover fairly slowly. (I'm in upstate NY in a Lake Effect area where winter tends to be fairly cloudy.) I'd like to try enhancing production with grow lights next year. I have some shop light fixtures and full-spectrum CF plant bulbs. I have a few questions:

How far above the plant tops should I keep the grow lights?

Is it OK to rotate a couple of grow lights among several boxes of plants (For instance, each box might be under lights for 4 hours/day...)?

Has anyone grown lettuce under lights? Our attempts to grow lettuce in the winter greenhouse have failed so far; I'm guessing it's light not temp. that's the limiting factor.

Does adding white reflectors around the sides substantially enhance the amount of light plants receive?

Any suggestions would be greatly appreciated.