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Yes, that sounds a lot. Theres a whole mathematical formula for Lux drop off, but I don't know it off by heart. Something like the drop off difference between 12" and 24" is 4 times or something. I suspect that at 2 ½' you may get more lux with a 250HPS at 12".

I have my 400 HPS at 35cm, or 12 ½".

I'd like to get it even closer but 27-28C is as high as I want to go.

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