like to encourage leaf growth
 

Ron,

For plants that I would like to encourage leaf growth, I was planning on using a metal halide light, as learned from your site, to promote leaf growth on certain plants. As long as I keep the environment stable, can I keep the MH light on 24 hours a day without harming the plants? Will this actually increase growth? Thanks Ron, great web site dude!

Yes 24 hours is OK. Plants only need a dark period if you want them to flower unless they are like tomato plants which are indeterminate which means they grow and produce fruits continually.