315 CMH distances

8 inches is too close.

I have foxtailing tips in the center of a bush, I dropped her too low and it shows.

Penetration is key at this point so I will probably defoliate.... However I have raised it to 11ish inches.

Before I can say I've truly researched this light I'm going to have to use multiple in my application.

Update on 315w distance to the canopy. If you have two in a relatively small area (mine is 4ft x 3ft) you have the combined light from both bulbs hitting each bud. In this case the intensity and heat is considerably more and so the distance needs to be greater. Regarding overall heat, the two 315's puts out equivalent heat to a 600w hps.

Its recommended to run a minimum of 37w Sq/Ft in Veg, and Minimum of 43 in flowering.

Having said that.

If 1 uses a 1000w Hortilux HPS in a 4 x 4 area at 24 inches youre getting 62+w Sq/ft, and 1600umol, and 145,000 lumens.

By comparison, the Sun, at the Equator, at the brightest part of the day is 10,763w Sq/Ft.

Theres really no such thing as to bright, but theres such things as to much Infra Red/Heat, UVA/UVB, Not Enough Air Flow.. BIGGIE THERE. Gotta have lotsa air.

I use a 1000w Hortilux HPS for seedlings at a height of no more than 24 inches, and have never had 1 problem.

I run a 1000w Hortilux at 18 inches from the top of the canopy, and cover right around a 4 x 4. Really really intense in a 3.5 x 3.5 but is stretchable to 4 x 4 at 18 inches with 2 big plants per light, each getting a 20 gallon container with Promix BX. Or 1 huge plant in a 30 gallon. Get 2lbs+/1000w Hortilux.
NO CO2, only good airflow, and many fans running 24 hours a day, in flowering, and veg.
I also train the plants to run horizontally, and train all side branching. Theyre like huge indoor Forsythia bushes in 20 gallon containers.

I can easily see where 12 inches should be no problem for the 315, and like some say, maybe closer.

In a 2.5ft x 2.5ft area, and 315w CMH will be right at 50w Sq/Ft. 12 Inches would probably be a good distance.
315 divided by 6.25sq/ft is 50.4w Sq/ft. Good enough to grow most any strain. But with 315w, you have to watch how tall. I would bend them/it over, and grow a nice plant, or 2, horizontally, letting the side branching become mains, a 10-15 gallon container. I myself would grow 1 good female. And Maximize it, in the biggest container I could fit in there.

I would experiment, and get the bulb as close as possible.

While I dont recommend this to beginners.

I try and find the burn distance, and then back the light off far enough so its not burning it anymore.

I just figured out Gavita means what they say when they say not to put their 1000w any closer than 36 inches. And they mean it. My buddy experimented, and was running them just fine at 38 inches, and put it down to 35 inches, and within a day and a half, they showed light stress, which was more Infra Red. Gavita has 2x IR vs a 1000w anything else single ended HID. But he expected this, and was waiting for it. Didn't hurt them, but they mean no closer than 36 inches. Even 38 may be better.

But then again I can get a 1000w Hortilux 18 inches from the top, and in reality am getting as much PAR vs what the Gavita can deliver at 38 inches, but the Gavita at 36 - 40 inches covers 30sq/ft vs 16 for the Hortilux at 2 feet and 1600umol, but at 18 inches the umole goes up bigly. Gavita at 36-40 inches puts out 2100umol. Hortilux at 18 inches, is probably similar, but only half of the IR.

Remember, the Sun is 1000w Sq/ft at noon at the equator.

these gorilla bubble, bx2 were at 32 inches most of the time , did lower for last three days but there out now under 1000 watt gavita, mostly I just leave the 315 full height,

4 315
About 16" canopy distance
Week 7 of a 68 day run
1400ppm co2
Another killer run.

I'm on my 10 run with the 315