This section is Newbie Central and it's a good question. Being a newb also, I don't have your answer, but am interested in what the more experienced growers think.
I added a small humidifier set on a medium setting. My humidity was at ~15% before, and is about 30% now with lights on. The humidifier goes off with the lights, and with the cooling, my humidity gets up to about %50 with lights off.
I would be interested to know if I am in the "healthy" range.