Jeff zone 8 N.C.

As you lower the light it will give a much smaller light footprint and so you will not be giving light to as many plants or as strong light to the ones at the outer edges. I burned the white part of my AeAe banana leaf at about 35 cm. It was not burned badly just small spots. I noticed that the leaf felt warm. Feeling the leaf to see if it is too warm after the light has been on for a while might be a good way to check for a safe distance. My 1500 watt light, set to 75% output is now about 42 to 60cm from my bananas (different height bananas) and they are growing fast with no burning.