Good way to raise humidity is ...wait for it...

plants.
If you have a grow area with just clones or seedlings you may want to introduce some houseplants. Water them as needed and return them to their regular window or shelf when the grow area fills up. Another option, an aquarium. But even easier, you will need a fan to move air around, take a wet towel as a wick and hang it from a rack (DIY) into a pail of water and put this arrangement off to the side of the fan. This will add humidity to a small area.

ADR, post your own thread and you'll get answers. Like, 7" from a 400 watt MH is close enough to fry a mature plant, let alone a small young one. Average would be 18", more or less. Unless you have an enclosed, cooled, hood.

Good luck, guys.