Donny Burger 1st

trial and errorr. 16-20" is usually a good range...when other factors jive well together, hanging distance is best choosen by resulting area of coverage -- how much difference is the central readigns from the readings along the edges - a simple klux app can do this, or you can use an app that converts it to ppf/ppe, but for this endeavour there is no benefit and there is a +/-10% error on that conversion due to variances in LED grow lights. any light measurement can give you proportional intensity differences from center to edges.. is it 50% of the central reading? is it 66%? are you sacrificing overall average to even out the light? Their "PAR" maps can help choose hanging distance too. umol/s of PAR and hours of operation are proportional to resulting DLI. DLI is what matters. "35" DLI is 35 dli regardless of how big the garden is or how many hours the lights operate. Learn about Daily Light Integral and avoid a tone of bad advice, lol. Many people look at one factor without considering the other. This is like miles per hour without duration of travel time.. the distance traveled being an analog to DLI. Rate x time = something useful. One alone is mostly useless. These are just good starting points. No matter what, your local climate will cause variance. You will always need to observe and react to the plant for fine-tuning adjustments. The developing distance between growth nodes is your guide to adjust the light. Too tight = need less light. Too lanky = need more light. That's how you find "Your" goldielocks zone. if not intimidated my math, read the DLI wiki page. Check out your umol/s production of the light, assume it's focused on the proper area (hanging distance) and shoot for 35-40 DLI to start. The percent dim should nearly 1:1 correlate with umol/s output. FC4000 of course mars is now limiting useful information. they don't give umol/s tech details or diode count to verify if they are lying about efficacy... Let's assume they are not lying. 2.85 * 320 watts = 912 umol/s PAR output from the diode. 8ft^2 / 10.764 m^2 = .74 m^2 coverage 912 / .74 = about 1200 PPFD maximum in 8sq ft tent -- actual is less than this due to missing plant or absorbed into walls. That's baked into the suggestion already given typical hanging distances. This is a shit ton at 100% for 8sq ft (about 52 DLI). Refer to any DLI table to shoot for 35-40 DLI 12h @ 900 ppfd = 38.9 DLI 900 /1200 = 75% -- with ambient co2 conditions, 75% in a 4x2 over 12 hours is as much as you need. 18 hours @ 675 PPFD = 38.9 DLI (1:1 inversely proportional to hours of operation) 600/1200 = 50% -- with ambient co2 conditions, 50% in a 4x2 over 18 hours is as much as you need. These are starting points... May need slight adjustmennt from there. Also, unlike their suggestion of 12", i'd go to 15-16" hanging distance, minimum. If you have a poor climate, you may want it even higher or slightly more dimmed. The plant growth will scream it at you eventually. for 12 hour operation and ambient co2, the max coverage of this light is closer to 11 sq ft as opposed to 8 sq ft. This might be better in a 3x4 space and some room leftover for equipment or avoid contact with walls. heh, usually mars has better starting suggestions. Their suggestion seems to be based upon 1200-1300ppm of CO2 and not ambient co2. plus, an improper vpd (temp and rh) will result in less potential photosynthesis per day (i.e. lower DLI maximum before damaging/stunting). If you were supplementing CO2 it's well-tailored for a 4x2 area. more is not better. the right amount is better.