Lighting 315W CMH distance from plants

[SHRED]

I love this light.
As the plants get older I drop the light closer to the plants ending with about 18" from them.

I'm wondering if this is that beneficial?
I'm looking for ways to keep it cooler in my tent and raising this light would help.

Any thoughts?

 

[dennis000]

For one 315w bulb
10cm 1567PPFD
20cm 841PPFD
30cm 628PPFD
40cm 422PPFD
50cm 278PPFD
60cm 212PPFD
70cm 161PPFD

It is better for you to keep the PPFD higher than 200 for growth, but too close the heat will hurt the plants.