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Metal halide, how far from the plants to out my light?

Justosmo

Justosmo

I have a rather nice and expensive metal halide grow light I borrowed from my father about 7 years ago and I'm just using it finally. I set it up with some plants but I'm unsure how high to keep the light from the plants.

It seems dark in the picture but I took this before the light warmed up.

Currently have it about 2 feet. Going to keep good air circulation to avoid heat.

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How many watts is your light? And what is the [average] temp at the plant level?
 
Fact is that you can have it as close as the plants can handle (this changes with acclimation) as long as it doesn't get too hot. The closer the light, the more intensity the plants will receive = more growth. Just don't burn your plants!!
 
Main factor, imo, is heat. The plants can handle sunlight (if acclimated properly) which is way more intense than any bulb.
 
mrgrowguy said:
How many watts is your light? And what is the [average] temp at the plant level?
 
Fact is that you can have it as close as the plants can handle (this changes with acclimation) as long as it doesn't get too hot. The closer the light, the more intensity the plants will receive.
 
Main factor, imo, is heat. The plants can handle sunlight (if acclimated properly) which is way more intense than any bulb.
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Thanks for the input. I'm unsure of the wattage off the top of my head but 400 sounds right if I remember correctly.
 
If it's 400, in general, the way you have it set up looks just about perfect. Just don't let them get too hot and watch for any leaves getting too light (sometimes leaves bleach if they aren't used to that much light) or edges getting crispy.
 
The plants will tell you how they like it, they just take a while to get their point across sometimes. Although, that's a good thing. Sudden changes are usually the worst.
 
mrgrowguy said:
If it's 400, in general, the way you have it set up looks just about perfect. Just don't let them get too hot and watch for any leaves getting too light (sometimes leaves bleach if they aren't used to that much light) or edges getting crispy.
 
The plants will tell you how they like it, they just take a while to get their point across sometimes. Although, that's a good thing. Sudden changes are usually the worst.
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Thanks. At this stage if growth how much light should I let them have.
 
If you mean hours per day... That's up for debate and I'll let others answer that. For my seedlings, they get 24 hours light. But I use T5 bulbs which are much more energy efficient. Some people say 24 hours is good, some say the plants need to 'sleep' for x amount of hours...
 
Which is correct? I dunno.
 
One thing I do know is that my plants do just fine.
 
My indoor vegging plants get 20 hours on 4 off. Mostly for $$ and heat reasons. My indoor is in my garage, so it still warms up in the late afternoon.
 
.
 
mrgrowguy said:
If you mean hours per day... That's up for debate and I'll let others answer that. For my seedlings, they get 24 hours light. But I use T5 bulbs which are much more energy efficient. Some people say 24 hours is good, some say the plants need to 'sleep' for x amount of hours...
 
Which is correct? I dunno.
 
One thing I do know is that my plants do just fine.
 
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So anywhere from 18-24 hours is good. Thanks alot for your input.
 
get a lux meter app on your smartphone (not super accurate but whatever) and measure it at different distances to find best height. 
 
hid lights dont need to be that close.
 
True, but 4-6 feet from a 400 watt MH will very likely be far less than 20k lumens.
 
My 600 watt hps can sit at 18-24 inches from (mature plants, not seedlings) plant tops and I get anywhere from 30k-50k lumens. My target for mature plants is around 40k. - personal preference I guess. I like my seedlings to be around 20k lumens until they get about 4-8 inches tall, then I like to increase. (I do this under 2x 4' T5 bulbs that are about 9 inches from brand new seedling tops - plants that just broke ground)
 
4-6' is definitely safe for seedlings, maybe even overly safe. I think you would be perfectly fine being closer to 2-3 feet, but that is as long as you don't over heat the plants and the plants can handle the intensity. Your plants look to be right at the cusp of being able to take on real lighting (well most of them). If you just put them under a 400 watt mh after being under a fluoro their whole life, they may not like the drastic change, but if you acclimate them (lower the MH light slowly) you could in theory almost touch the plant tops as long as it doesn't get too hot (which it would be super hot, thus people never get that close).
 
And juanitos is correct, they don't need to be that close, but they can be that close and the chances of hurting your plants at 2-3 feet are slim, as long as 1) it's not a drastic change and 2) the temps stay regulated.
 
You will get more out of your plant with higher lumens, but I'm used to pushing canna plants to get the most out of them. People don't usually need to push pepper plants too hard though.
 
edit: I'd suggest to put the biggest plants in the center, that is where you get the most lumens (the bigger ones can handle more), that way the ones that can utilize the light the best get the most and the smaller ones that may not like that much light can be at ease. Put the smaller seedlings on the outside until they get a little bigger. Once they're all bigger, I would move the bigger ones to the outside and the smaller ones in the center to get a nice bowl-shaped canopy to even out the amount of lumens they all get.
 
 
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Read the plants - if they start to wilt at any point under the new light, they may be too close (or, too hot).
 
This should be posted in "Grow Tech" where:  Discuss lights, heaters, irrigation systems, greenhouses, and DIY solutions. Show off your inventions!
 
I think it goes well here. He isn't talking about a model of light, or the vendor or performance of such, just how far he needs to put the light to grow his peppers...
 
willard3 said:
This should be posted in "Grow Tech" where:  Discuss lights, heaters, irrigation systems, greenhouses, and DIY solutions. Show off your inventions!
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Sorry but I didn't think it did. Not asking g for advice on lighting options. Just how far plants like the light.
 
I run my 400W metal halide between 12" and 18" with a small fan that pushes the heat away from under the hood. the room is ventilated with an exhaust fan to maintain approx 22 degrees C average as well. I have no issues with this other than some "edema" once and a while which is caused from my pot size being to big and retaining too much water in the early stages. hope that helps a bit. 
 
Edit: I just measured at 12" for 3 healthy plants. There's no need for me to raise more than that with the fan blowing on the plants.
 
My current grow setup indoors is an interchangeable ballast to run 600w hps or MH I usually start the seedlings out for the first week or two with the MH and than change to the Hps, as the Hps puts off more lumens and more heat. I hold my lamp around 24-30 inches above my plants tips and in general I hold a temperature of 72-75 degrees with my fan running for ventilation and plant movement. As someone mentioned above it is all about heat as your plants can take the lumens. I've had my bulb down to 18-20 inches at nights where it is colder, just measure temps at plant tops. I like to feel the leaves honestly, this lets me know a lot of factors I can't see with my eyes at times, especially under those bright ass bulbs!

I usually start my trays with the bulb super close for extra heat, around 82 degrees. And than raise it once they sprout to a distance that gives me 75 degrees. Than further more as the plants grow to keep temps optimized and not too hot at plant tip. With my tomatoes though once they sprout they go under the light but it is about a foot further away than when I start the peppers as I like to get leggy tomatoes because I bury the stems.
 
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