12-18 inches is standard hanging height. I have a 1000 watt equivelent LED that does well at 50% for germ and seedling, 75% for veg and 100% for flower.
This thread will teach you about DLI and how to measure it using a free ap for your phone called photone (was called corona just prior to the pandemic) its an excellent read, one of the most informational and popular threads here on the boards. Ots an indepth explanation of what @BigCat420 is talking about.