Distance from 400w HPS and plants?

This is a very simple answer and a very, very common question. Hopefully, the next person will find your thread when they search for the answer:

The height of your lights, whether CFL, HPS, MH, MV, fluro tube, incandescent, LED, or Christmas, is not a question of how much light is too much. There is no such thing, get the damn things as close as possible. The only problem you run into with putting the light right on top of the plant is the temperature the light gives off. This is why HPS and MH are the best. HID (High Intensity Discharge) lights give off mostly light and relatively low temperature, so the plants are happiest. Incandescent lights (regular light bulbs) give off a mix of light and heat, so you can't put them as close and the plants end up stretching or burning.

So find the minimum height by putting the back side of your hand about 12" from the light for about a minute. If it feels hot, try 15", if it's still hot, 18", etc... until the back of your hand is just warm.

Most people use fans to circulate air, which is good for letting the plants give off their O2 and pick up new CO2 and to thicken up stems. The other good thing about moving air is it will keep the plants cooler, meaning you can get the light closer. If you have an indoor/outdoor thermometer (or even better hygrometer), put the outdoor sensor at plant level and use it as an even better way to keep track of how hot the plants are. Keep temps between 72-80.

So the answer is keep the lights as close as possible while keeping their temperature (not room temperature) between 72-80F.

 

Mine is about 20 inches

 

Rule of thumb

16'' for 400w
24'' for 600w
40'' for 1000w

Good luck with grow man!!!

 

Oh yeah, one more thing, HPS is for flower, MH is for veg... Do you have a switchable ballast? Get an MH bulb if you do. If you don't, get an MH conversion bulb for an HPS ballast. You're in the wrong spectrum of light for vegetative growth.

PS- my 400W MH is about 12" from my youngest plant (10 days) and about 15" from my oldest (25 days), got some catching up to do.

 

I have a 400w hps and I say keep it about 25-30" away. I just got a new bulb and I had it about 15-18" away and my leaves started wilting. I moved it up to exactly 2 feet and they popped right back. Like everyone says, it's a heat issue. Even with 2 fans blowing on them, they were still way too hot.

 

I think you see such a discrepancy in light height mainly from the type of reflector people use. I have a Yield Master II 6" Supreme, which basically has two 6" adapters to connect to cooling ducts... I have my bathroom fan connected to the socket side to create some suction and another duct going out the bathroom door through the hole in the door where the door knob used to be... This allows my fan to draw in 71F (central air thermostat controlled) air from an unused bedroom into the light reflector up and out of the grow room. Since the reflector has a glass cover, most of the heat is drawn away out of the room before the plants get a chance to feel it. The resulting temp in the room is about 75F on average with 77F at plant level. The more you can isolate your heat sources, the more control you'll have over heat and the closer you can have your lights, and the better your plants can grow (assuming water, nutes and pH are properly maintained.)

SexyStaci (damn, not a better thought than a hot girl growing dank!!), what kind of reflector are you using? 400w of HPS at 2 feet away seems like there's going to be some serious stretching since the spectrum is off and your lumens will be lower (distance related). One strategy might be to get one of your fans blowing straight up to the light bulb if it's open to the rest of the room. At least you'll be sure to get the heat to go straight up to the ceiling instead of being trapped between the plants and reflector...

 

It's easier to just show you a picture. it was from HTG, it's a hammered aluminum 6" non-cooled. As for stretching, not even a little, these plants are bushes. Although this grow is a mystery since my clones weren't even clipped yet. I had 4 mixed plants from really decent seeds, but when my friend gave them to me they were all mixed up! When these are done, the good, identified clones will be put in place.

Maybe it's because the bulb is brand new, because I've had the light lower before. But I assure you they were wilting, 1 day after I raised it they made a 100% come back.

 

I stand corrected, those are gorgeous!!!! Do you have a journal? What day are you on? LST, topping, fimming?? Quite a nice bush there SexyStaci if I do say so myself, mmmmm.

I'm a believe of if it ain't broke, don't fix it, but I wonder what they would look like with MH and the lights closer. I know not everyone can go out and buy all the shit for a "perfect" grow, but I think it's pretty much agreed through all the experiments that more experienced people have done over the years that the ideal spectrum is MH... Fuck it, all this shit we're growing is better than the vast majority of what you could buy on the street, so I guess it doesn't matter.

Moral of the story: It's all about max light, controlled temp and RH, good pH, nutrient availability and letting mother nature do the rest. The details are just that...

 

I have a brand mh conversion bulb, but I didn't want to use it on this grow. Once again, I have no idea of what these are. They could all be boys for what I know. I have two rooms, a vegging room, and a flowering room (10x10). I did the vegging room first and it is very nice, clean and workable. This room is around 80% finished, but those plants were taking up too much space in the vegging room, so I figured I'd just let em go and hope for the best. They have only been in there for 5 days. I'm gonna go 12/12 on April 1'st. It's easier for me to remember that way. When they are finished, I have 6 beautiful clones to go right in. All sexy girls They will have the mh conversion to veg, and the hps to flower.
See, pretty girls can grow too

 

Which is a piece of crap btw. Not even similar to the one they had advertised. The one in the ad picture looked like a mirror, just thick and solid. This weighs about an ounce and my fans can actually make it sway! I was going to complain about it, but that's what you get when you go for the special deal.

 

I have a similar question except im using a 250 watt HPS with the ballast built into the lamp with tempered glass, right now its about 12 inches from the canopy sinced I lower it down from 20 inches after reading I had it too high, However I read a max temp of 86,2 degrees F and 82 avg with the lamp on and 75-76 with lamp off. Is this ok or should I raise it up to say 16 inches? With the lamp higher at 20 inches it normally doesnt climb past 80 for the reading of max temp and is 78 avg with lamp on. I have both a vent fan as well as an oscillating fan.

 

What was your bottom temperature with the light at 20"?

If it was lower, then yes, raise it up. If it was the same, then it's your fan/vent setup that isn't getting enough air moving around.

Where are you pulling your fresh air from? What's its temp?

Out of curiosity, what light schedule are you running? I've decided to go with the 24/0 just because the plants seem to have been doing really well under it and I had a failed try at 18/6 (heat related though)

 

Bottom temp was like 75 on a hot day, I have no a/c and am pulling air from outside in and ventilating into another room where it gets expelled. I was running a 16/8 schedule but I'm in flowering now at 12/12. When its a cold day (which is almost never) it can drop pretty low like 55 or 60 but on average was at 78.

 

I don't think there is any perfect, specific height. Sometimes people make so much of a big deal about things. It's pretty simple. Start at 15-18", if the leaves start to look wilted, move it up a little, if not, leave it alone. I was never the type to be strategic about a plant. If it's thirsty, water it. If the lights are too low, raise them. I can honestly say that once I knew what I was doing, I have never had a failed grow. And I do not sit there with meters and rulers trying to get the perfect crop. The only time I use a ph meter is when things aren't right. I personally don't think it's that complicated, unless you want it to be.

 

HEY I HAVE THE SAME HOOD TOO! 400W HPS FOR VEG AND BLOOM. cAN I ASK IS IT BAD TO PUT MYLAR UNDERNEATH THE POTS FOR MORE REFLECTION, AND ALSO WHAT SHOULD MY WATERING BE LIKE? RIGHT NOW I GVE THEM REALLY DILUTED NUTE WATER EVERY 1-2 DAYS.
IN VERY SMALL AMOUNTS. SHOULD I GIVE THEM PLAIN WATER IN BETWEEN OR WHAT? THANK YOU VERY MUCH, IM GROWING INDICA/SATIVA FAMILY LOVE.

 

yes there should be plain water every other feeding