There's a lot of 'more light is better' going on in this thread... which I just need to contest...
Optimal light output is optimal and optimal light output is generally between 30-35 true watts per square foot.
Now... more with a dimmer...? That might be better. But only arguably... in the scenario in which you intend to increase your footprint.
I think coverage is better, catching as much of what ever light u have is certainly beneficial. I have a 3 way multimeter that test light, soil and ph. I turn it on the light selection and although I dont know how to read it accurately, I just wave it all over my grow and am satisfied when it is 3/4ths to all the way pegged everywere I put it, seems to work pretty goodI mean it'll do until I get a par meter.