m0useanswered grow question 3 years ago snip it from an article.
315W is the most popular size for LECs/CMH grow lights. Both the 315 LEC and 315 CMH grow lights should be kept at least 18″ from the top of your plants, with some models needing to be kept as far as 3 feet away.
https://www.growweedeasy.com/how-far-grow-lights#lec-cmh-grow-lights-distance-plants
I would suggest consulting the manual for your unit.
See if their are any generalized PAR light maps for your model as that will give you a good idea for the height it needs to be hung.
If this info does not exist ask the company for technical data on it, they should be able to provide something.
best of luck