LEDgardener

Hey gang,

I have about 440W of bridgelux gen 2 strips running around 800mA without heat sinks.

I noticed some buds had begun foxtailing weeks after I commissioned the strip light fixture (from a blurple led light).

The height I set the lights was admittedly quite low (within 3 inches from some of the buds that stretched out).
I've risen that to 9 inches from the top of the canopy.

What height do you run your strip lights?

1) Measure the length x width of the light fixture. If in inches divide that by 144 to get square feet of light fixture
2) Take the amps that your light runs at and times it by the voltage - this will give you wattage of light
3) Divide #2/#1 to get watts/sq foot, I've had success with 30 watts/sq ft for flower at 18 inches

At 13 inches I was getting definitive light stress, at 15" some minor light stress and at 18" none with some room for plant to grow up into. Once stretch is done you could move it down to 16".

Alternatively if you wanted to conserve on your power bill, with a sog/scrog you can reduce the wattage from 30W/sqft down to 20W/sqft and lower the light distance from 18" down to a lower height above plant. I wouldn't recommend doing this if your plant is quite tall but if your doing it with training techniques would work well with a well manicured horizontal grow.

Awesome, thanks man.
I'm running a scrog just shy of 30w/sqft.

Very good intel.

Raise lights for this grow but for future grows dial down the wattage.

Nuggie wrote: ↑

Mon Nov 11, 2019 11:27 pm

1) Measure the length x width of the light fixture. If in inches divide that by 144 to get square feet of light fixture
2) Take the amps that your light runs at and times it by the voltage - this will give you wattage of light
3) Divide #2/#1 to get watts/sq foot, I've had success with 30 watts/sq ft for flower at 18 inches

At 13 inches I was getting definitive light stress, at 15" some minor light stress and at 18" none with some room for plant to grow up into. Once stretch is done you could move it down to 16".

Alternatively if you wanted to conserve on your power bill, with a sog/scrog you can reduce the wattage from 30W/sqft down to 20W/sqft and lower the light distance from 18" down to a lower height above plant. I wouldn't recommend doing this if your plant is quite tall but if your doing it with training techniques would work well with a well manicured horizontal grow.

@Nuggie what strips or LED’s were you using and at what amperage or how many watts for the 18” of space with no stress if you recall?

Vests strips run at 0.94 A on 8 strips on a 6,25 ft sq space with 30 w per ft sq and 18 hour day.

I was running 30W per sqft in a 4x8 space. Strips running about 1A each, one fixture 480W covering 4x4 and two fixtures 240W each covering 2x4.
I had my lights suuuuuper close relative to @Nuggie . Some buds stretched past the lights. Many were within 3 inches or less.

I don't have a lot of free space now so I've dialed the lights down to their min (which is 50% of their maximum) to around 480W total or 15W per sqft. I also raised them up as high as I could, around 8-12 inches.

What do you think? Is this enough?

Its going to be experimental, there is some variance from strain to strain as well. The first sign of light burn I find is not the brand new leaves but the next two sets down they have seen more time under the light have their serrations point upwards relative to the fan part of the leaf, its very subtle and its not present on all top leaves, check this by about midday to three quarters thru day. ALL the top leaves can droop near end of day and at this point you won't see the tipped up serrations, it's like the leaf at that point has been exhausted (outside of watering problems) If it gets real bad the top most leaves will turn yellow. Look for the serrations tipping up as the first sign and judge from there. I'd leave it at 12" for three days, dont see serrations tipping up then lower it until you find the threshold. go lower by an inch every three days until you see stress signs and then raise it from there by 2 inches.

If the height constraints are really limited then next grow I would include more blue light in veg and the first two-three weeks of flower to limit stretch and then for rest of flower hit it with higher red to dense up your buds.

I'm glad to see this question as I was wondering the same thing. A growmie was just telling me he does 10-12" with his gen 2 based fixture. I haven't heard any other's experience.

I'm around 30 watts per sq ft and try and stay about 8" - 12" during flower this is my first run with these lights though and 2ft prior to that and close the distance slowly. Have them in a open room with the light spanning most of the space
with some ultra pure white paint on the walls.
I had them all at 6 inches and had one indica strain crystal candy that was starting to bleach and foxtail at the second set of leaves like was mentioned above.
So..
I backed the lights off a few inches and am going to to try and stay around this height for the rest of it. But I'm running all of them around 700milliamps or less and have had some hazes grow very close and not suffer the wrath of bleaching. This is with 3k and 3500k gen 2.

I have since adjusted height and keep them between 16 and 20 inches going of what Nuggie had said to me and they seem very happy.