How Far away from Plants to put my HPS?

Discussion in 'Growing Marijuana Indoors' started by 1r0n1ungs, May 9, 2006.

  1. Got me a nifty little 400w HPS from inside sun recently, and they're presently about 1.5 feet away from the plants, too close? too far? temperature seems to be ok for now too. Any Insights?
  2. Good rule of thumb in my experience out your hand on the top of your plants too hot? if its to hot for your hand its to hot for your children I go about 24-36 inches from the tops. You might also hold a thermometer over them for a minute and see how hot it is keep it between 70-85 deg. F. Let us know how it goes.

  3. i got a 400 hps,, and id say the same thing this fellow did....
  4. No no no. You with good ventilation you can get that light much closer than 24 inches.

    I have my light 10" from my plants with average temperatures between 82-85 and maxes out at 90 for an hour or so a day.

    The hand rule is a good guide to go by. And a temperature with a probe works great. Just make sure to shield the sensor from direct sunlight as it will give you a false, really high, reading.
  5. true , my lights about 16'' away, but all my plants are different heights, got some sitting on blocks to hit the light evenlly, with the tall ones... check em out...there down below..... click it!!
  6. if they are still young seedlings I'd start off around 3 feet just to be safe. I had mine closer and they started to burn and one of them died from it... with two others looking a little ragged. Right now I'm playing it safe keeping them far away and as they get older I will slowly raise them up closer to the light (I have my light in a fixed position and put things under the plants to raise them closer to the light)... even at 3 feet, they aren't stretching at all. really shows you how much more powerful these are than flourescents.
  7. With a 400 hps, 8 inches from the bulb to the nearest vegetation will equal the intensity of noon time sun at the equator.
    Plants will always need to be introduced to intense light gradually. And excess heat will harm them.
  8. I live by the "hand rule". My 400W HPS is about 5" from my canopy in one of my cabs (but I use a SunTube to cool the bulb). So there is no hard and fast "distance" rule. It depends on your situation and conditions.

    If you have a nice crossflow fan running between your lamp and plants, you can get a lot closer. If you use a SunTube (like me - or a CoolTube), you can get your lamp right on top of them. The only reason my lamp isn't closer, is because I wouldn't be illuminating some of my plants on the perimeter.

    On the converse, if you have poor ventilation or if you're growing somehwere hot, like in an attic, you might have to have those lamps 4 feet from your plants. It just depends.

    That's why I use the hand rule. I even have a laser temp gauge, but come on. Use the hand rule.

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