Metal Halide for Soil Setup

400W metal halide for a 2.5x2.5 area. Was 8 inches from tops of plants with temps ranging between 80-85 daytime. The only ventilation is 1 12 inch oscillating fan blowing on hood and plants. Another oscillating fan blowing fresh air into the room.

I have seen alot of posts saying put it as close as possible and still maintain reasonable temps. I understand my temps are at the threshold of being too hot. The plants seem to be developing fine overall. The There are a couple yellowing and curling and a couple doing perfect. There was no stretching on any of them. Since they are showing inconsistent results i began thinking about raising the hood to about 2x the distance as before. this would be 16 inches from the tops of the plants. From what i have read 18-24 is ideal for a 400W MH.

Should i raise it or leave it?

I have a 400W HPS lamp just 12 inches from top & plants seem to love it - I also have fan blowing onto top of plants & lamp & one fan sucking clean air in

edsthreads said:

I have a 400W HPS lamp just 12 inches from top & plants seem to love it - I also have fan blowing onto top of plants & lamp & one fan sucking clean air in

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me too and it all seems ok,they say to put your hand where the plant tops are and if it burns you its too close
Bifter

that's so weird, I can't put mine closer than 2 feet to the tops of my plants or the temp goes above 90 and it's uncomfortable to put my hand there.

I raised it to 16 inches from the tops of the plants. I noticed the thermometer read even higher temps than before(90-93ish). However, the leaves are curled less and are less yellow. Before i moved it i thought the light felt fine on the back of my hand. I think the temperature readings before were from a poor location relative to the plants.

Is 85(the best i can achieve with both fans on the plants) too hot for growing without CO2? And if so can i really raise this light more without thinking about supplemental lighting? I guess i should throw in that they are all seedlings currently about 2 or 3 inches in height and 25-30 leaves each.

good ventalation is key i keep my 400 no more then 6 inches away......

420101 said:

good ventalation is key i keep my 400 no more then 6 inches away......

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Exactly. I have cool tubes and have had my 1000w lights 2 inches away at times. The light mover helps you keep it closer too. But for a 400w I would say atleast 12-14 inches if its a bare bulb.

the bulb is in a vented hood but there is no duct hooked up to it. Cutting the house is not an option so i am trying to use fans to control the heat. This is not the best way to go about it but is the best i can do. if i am only supporting 4 plants and expect to reduce to the best 2 before the end(unless they all turn out ok or better and space allowing!) will i need to think about supplemental lighting at <= 18 inches?

i think you got lots of light to meet your needs and i keep my 400 6 inches above without a vent hood just check using the back of your hand at plant level thats were i check the temp too

got a fan for it and the plants can touch the glass fine. great investment