HPS Distance to Plants

I know this subject has been brought up several times before, but I'm hoping to get a lot of feedback from experienced growers who have settled on a specific bulb distance that they consider safe for their plants. I'm still trying to decide whether to use the 600W or 1000W HPS. Assuming that you have adequate cooling, how close to you put your bulb and which type of bulb do you use? Thanks all.

What the of fixture? i.e. is it s cool tube?

as close as possible without burning them. Air cooled hoods get you closer.

Just start lowering little by little until you see the top leaves start to react by curling at the margins Or anything out of the ordinary. Then raise it up a bit.
Make sure you dont forget to check on them frequently while you are finding the sweet spot.

Just remember they can grow very quickly so leave a few extra inches
for a buffer zone.

Start with a safe distance.

There is always the hand test but im so tough it don't work for me.

When I ran a BLOCKBUSTER 6" air cooled hood the glass could touch my plants without burning them.

However light bleaching occurred.


I've used a 600 with air cooled anything from 6-18" away from canopy.

Non air cooled. 600w 12-18" away. Up to as much as 24-36" away when growing seedlings/young clones.


I keep my current 400w about 8" away and its not air cooled.



J

My air cooled 1000 is at about a foot.
I also have strong fans and ac in the room

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I guess I should have specified that I am only concerned with light bleaching during flowering. My plants never get too warm.

I've already heard all of techniques for determining a safe distance by trial and error. Just interested in seeing everyone's numbers.

Thanks jondamon. Exactly what I was looking for.

I've got a box fan in front of my gull wing, it's about 8" from the tallest plant. Could get a couple inches closer maybe, but it's fine where it is. One of those $20 point & shoot thermometers from big box is really handy for this. Along with the plant's feedback, natch.
600W

bout like char said...12" ish. not more than 18"

sometimes as close as 8-10" but this is really pushing it.


for 1k

ive been dicking around with this for a wile. I suggest the 600 because the 1000 you will have to raise the light much higher and it will flood better but most of the 1000 light will be wasted out the sides . I pull the same yield from a 600 vs a 1000 In my set up. 600 much more easy cooled. light difference air cooled. 1000 watt 2 to 2.5 feet away 600 1 foot away. open hod 600 would have to be about 3 feet away thousand 3.5 to 5 feet away. open hood are the best if your not concerned about heat. most 99 % of them heat is a major challenge

Even when in cooltubes, avoid the red

*edit* oops, attached PH chart by accident, lol

I never really have issues with heat, but find that i am always battling that "sweet" spot when it comes to bleaching. Even using air cooled, it seems that 12" is about the closest (to bulb, not glass) that I can get before I have bleeching.

I prefer air cooled, but when I had an open hood, I never had any bleeching. I think it was because i never had It (too) close to the plants, as heat stress would show before light stress.

I always put my taller plants along the perimeter of my grow, and the shortest directly under the bulb.

Great info guys. Thanks.

My fixture is open, but with a dedicated fan pointed directly between the bulb and the plants, the canopy never gets above 80 degrees in the winter. In the summer it can get warmer (especially if I'm using side lighting), but I have a solid plan to deal with temperature issues this summer without air conditioning.

I had pretty good yields with a 600W in my first grow (random bag seed), and I had better yields with the 1000W with a typically low-yielding variety (Girl Scout cookies). The plants take up a 4x4 floor space, so the spread of the 1000W is better, even if it means sacrificing a little efficiency. I'm also considering a couple of 400W MH for side lighting this round instead of T5's, so a 600W HPS might be enough.

amgprb said:

I never really have issues with heat, but find that i am always battling that "sweet" spot when it comes to bleaching. Even using air cooled, it seems that 12" is about the closest (to bulb, not glass) that I can get before I have bleeching.

I prefer air cooled, but when I had an open hood, I never had any bleeching. I think it was because i never had It (too) close to the plants, as heat stress would show before light stress.

I always put my taller plants along the perimeter of my grow, and the shortest directly under the bulb.

Click to expand...

Exactly my concern. I used a ScrOG in the last grow, and that helped a lot in spreading out the taller branches. What size bulb are you using, amgprb?

FNG Grower said:

Exactly my concern. I used a ScrOG in the last grow, and that helped a lot in spreading out the taller branches. What size bulb are you using, amgprb?

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I have 2 grow cabs and a tent. The tent and one cab are both 400's and the other cab is a 600. I know it would be more efficient to do one larger room, but I like to experiment with different techniques, strains, etc. I also have two smaller cabs with LEDs that are used to house males (for pollen) and clones.
Currently all 3 are in flower.

amgprb said:

I have 2 grow cabs and a tent. The tent and one cab are both 400's and the other cab is a 600. I know it would be more efficient to do one larger room, but I like to experiment with different techniques, strains, etc. I also have two smaller cabs with LEDs that are used to house males (for pollen) and clones.
Currently all 3 are in flower.

Click to expand...

Nice. I like to experiment too. This round, I have three sister clones that are receiving slightly different bloom nutrients. They've only been in flower for one week and I can already tell a difference. Hungry little girls, they are.

FNG Grower said:

Thanks jondamon. Exactly what I was looking for.

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If light bleaching is your concern I've found 6" with a 600w to be that breaking point where bleaching occurs.

Its a bitch at times too, especially when temps are not an issue because you don't get tell tale signs of heat stress etc like leaf edge roll up.

If in veg its less apparent than when in flowering. I've had a top cola almost turn white.


J

1000W lamps are good if you have a lot of vertical space and want to cover a greater canopy area with fewer lamps. You will have to keep it farther from the canopy, but it will cover a larger canopy area.

600W lamps must be put closer to the plants in order to get the same intensity as 1000W lamps, and thus will cover a smaller canopy area. You will need more lamps to cover the same canopy area, but those lamps will be closer.

In general, getting closer makes it brighter, but shrinks the lighting area. Getting it "as close as possible without burning" isn't necessarily the goal. It's more important to have even light distribution over the entire canopy.

Good canopy planning is key to high yields.

jondamon said:

If light bleaching is your concern I've found 6" with a 600w to be that breaking point where bleaching occurs.

Its a bitch at times too, especially when temps are not an issue because you don't get tell tale signs of heat stress etc like leaf edge roll up.

If in veg its less apparent than when in flowering. I've had a top cola almost turn white.
J

Click to expand...

Yes,
Light bleaching is definitely one of the issues that I must confront, this grow.

First sign of discomfort - the reflector is getting raised.

Remember that you should be viewing the color of leafs under some other light other than HPS. Leaves are always darker shade of green than you think.

Remember, this thread is four years old.