400 Watt Metal Halide distance from sprouts

My plants just sprouted out of the top of the super growers starter plugs. I was just wondering how far should i have my lights from the top of my plants. I have it about 18 inches away now!!!!

It depends largely on your ventilation. Are you maintaining between 65 and 75 degrees? If so, a 400 watt metal halide can be placed up to one foot away without risking damage to the plants. If the air is not vigorously circulated, the heat is exponentially increased, anything above 80 degrees slows down growth rate with virtually no increase in size at 90 degrees. In that case, 18 to 24 inches. We are talking about seedlings, which means that a lot more light exposure reaches each sprout at one foot. With a fully mature plant, you loose some usable light to the lower part of the plant at only one foot distance, so the larger they get, the better you'll be able to evaluate maximum efficiency of lighting.

Start are 2.5-3ft and gradually lower it...

If they just sprouted you shouldnt have a 400 watt light on them yet.Use something like a florescent shop light for a week until the new tender sprouts get established then bring the light in about 12 inches above the young plants.Place your hand palm down on the top of the the plants.The heat from the lamp shouldnt be to uncomfortable to the back of your hand.You can lower it if the heat is comfortable to your hand

You are the Master, You have the power to grow it big and green or do it poorly and grow iot long and lean.

unless the plant turns yellow from heat, it is fine

Thank everyone for their help. I have placed my lights about 1 1/2 foot from the plants. And it seems everything is going just fine.

I just bought a 400 watt mh today for some young plants that I had started with cfls how soon should I notice a difference in growth

My 1 week old plants are 1 foot from my 400 watt mh light... as long as my temp are down (there at 75, i have ventalated hood) is it ok for them to be that close?

what damages the plant, the heat put out by the light or the uv from the light, or both?

milkmilk said:

My 1 week old plants are 1 foot from my 400 watt mh light... as long as my temp are down (there at 75, i have ventalated hood) is it ok for them to be that close?

what damages the plant, the heat put out by the light or the uv from the light, or both?

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and.. can i OVER spray my sprouts with water. is it a good idea to spray often while the plants are young and developing a root system?

i have a 400 watt HPS & i have it at 18 3/4 inches from my 3-4 day old short rider sprouts. I have started all of my 30 sumthing outdoor plants under it till the second true leaves started at about 75-85 f. None of them have died from heat or showed any signs of stress, just put 5 in bigger peat cups.

The main reason why you dont want to put sprouts under HID lights is not heat damage, but the fact that when they are that young under an HID light the high amount of light forces the plant out to fast and it will not develop an intricate root system. after a week under floros, the roots will be developed enough to switch to HID, do not start under HID, no matter what your temps or air flow is like.