Hanging height for led

So I’m on week 4 and I’m a new led grower I use to run hps how close can I have my 720w led above canopy the manufacturer say 15cm is this to close?

15cm? I'd be hard pressed to run my light at that hang height. Sure you can do it but there are a lot of reasons why I don't.

What light are you using and what's your setup like?

What brand & model are u using of led?

diff led‘s require diff heights and ur environmental inputs and stability also allow the user to do certain levels to being closer successfully vs someone if they don’t have their for exampke temps and co2 hugh enough if higher ppfd/light strength . also just because a company says u can use a strong amount of ppfd and be that close doesn’t mean every pheno will allow such or be degraded from too much light Inputs. Like nutes to enviromental , not every plant is same and it takes experience and I suggest starting at furthest distance that’s efficient vs being closest suggested . I know when I tried closest suggested even with co2 I def damaged many pheno’s without adjustments and enviromental changes.also a huge thing I didn’t have on point is knowing ur canopy/leaf temps and make sure that’s 24/7 correct , these things make all the difference and making things like raised light intensity worthy but also allowable of more inputs (not all pheno’s ).

are u running a stable vpd?

ab2t2000 said:

So I’m on week 4 and I’m a new led grower I use to run hps how close can I have my 720w led above canopy the manufacturer say 15cm is this to close?

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You go pretty close with those bar lights spreads the light better only like 1400 par right under bar

ab2t2000 said:

So I’m on week 4 and I’m a new led grower I use to run hps how close can I have my 720w led above canopy the manufacturer say 15cm is this to close?

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Stay 10 inches away just to be safe

i wouldn't get too close, most my plants dislike too strong led light and don't produce the same frost when blasted too hard with led. Usually i would put them around 15 to 20 inches away, although depends on the style of light like mentioned above.

I have 300w and at 30cm i get 1400ppfd....
If light is too strong worst case you get light bleaching best case you get foxtails.

I got 4 720w adjusta led in a 2.4m x 2.4m (8x8ft)

Will I still get good results at a foot or so away?

ab2t2000 said:

So I’m on week 4 and I’m a new led grower I use to run hps how close can I have my 720w led above canopy the manufacturer say 15cm is this to close?

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You kind of have to get your plants used to the led light. Alot of people have issues with this wen new to using led and struggle. Despite there being very little heat its so easy to completly fry your plants with led. Start hanging as high as you can and lower power and slowly increase and lower your hight . Once the plants get used to it and you get to know how to feed them properly using all the increased light then it gets really good.

Get yourself a par meter si you don't burn your plants. I run my 600 watt at 24 inches and can hit 900 par with good canopy penetration.

The wattage is only tenuously related to optimal light distance/height.
E.g., a 600w light in a multi-bar configuration can have a closer minimal distance than a 150w lamp with all its LEDs tightly packed together.

So I left my led lights in veg at the top of tent on 50% made my way up and on week 2 I went full blast just thinking will I be losing a lot there 3ft above now but I just lowered to 20inc on the guide of my led says it can be 11inch so I’m gunna see how they react but what I’m really thinking is if I leave em 3ft above will I lose a lot of yield?

ab2t2000 said:

I leave em 3ft above will I lose a lot of yield?

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If you scorch them you could lose more yield. So just go slowly and watch them closely.

3ft ? You think a 0.2w diode is the sun ?
LEDs are harmful to any tissue, due to their angle cones they are sometimes even more dangerous up close..
Also, leds consist of many many small low output diodes, for this reason they need to be as close as you can get them...
This is a tricky situation, the manufacturer is saying very close is best (and for a good reason)
But most plants will respond by probably dying from being that close to leds.
I had a 700w panel, avg height I had it was 10-15 inch give or take and it was fine on 80-100% output.

Depends if its a COB, a panel or a bar..
It's a bar so I'd take em to a 18" then lower to a foot if they don't react badly , which they shouldn't

ab2t2000 said:

So I left my led lights in veg at the top of tent on 50% made my way up and on week 2 I went full blast just thinking will I be losing a lot there 3ft above now but I just lowered to 20inc on the guide of my led says it can be 11inch so I’m gunna see how they react but what I’m really thinking is if I leave em 3ft above will I lose a lot of yield?

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All other things being equal, the more light you give a plant, the greater your yield. That's true as long as your plants are able to handle the amount of light you're giving them. In optimal conditions, cannabis will grow at 2000µmol ("micro-moles"). That's a staggering amount of light considering that noonday sunlight in, say, the Algeria is 2200µmol±. In general terms, the "light saturation point" is considered to be 800 to 1000µmol.

I couldn't find a PPFD map (PPFD is the amount of light falling on a given area in a given amount of time and it's expressed as µmol/square meter/second - think of it as the number of cm's of rain falling on a square mete though I use the annotation "µmol").

This page, reads " We've tested these LEDs with an Apogee PAR meter, and the PPFD outputs are around 1000-1200 PPFD across the canopy from 12" which is amazing!" Based on other info on the page, 1200µmol sounds like a good working number.

Per above, the generally accepted value for the light saturation point is 800-1000, and to hit the 1k mark, your grow needs to be in really good shape and the strain of cannabis that you're growing has to be able to take advantage of that amount of light.

It's better to err on the side of caution so assume that 1200µmol is a valid working number and we'll work backward from 12".

The amount of light hitting a canopy decreases very rapidly as the distance increases. At 12" the canopy will get 1200µmol (erring on the side of caution). If the hang height increases to, say, 14" the PPFD may well drop to 1100µmol. I've measured the drop-off at 50µmol/inch but, like so many other things with grow lighting, "it depends".

A big factor in LED grow lighting is that the closer the light is to the canopy, the less even the light cast will be. Based on that, it's tempting to raise the light to get the most even amount of light on the canopy but we know that raising the light just 2" can cause a significant reduction in light. "There are no solutions, only trade offs", right?

To my way of thinking, I would top and LST the plants to get the most even canopy possible and, once the plants are in mid-veg or later, run that light at 100% power at 14" or 16". That will get you about 800µmol in the center of the grow. Lacking a PPFD map, I don't know how the light cast will fall off at the edges but the 800 level is a healthy amount of light.

The onus is on the grower to "read the plant". If a cannabis plant gets too much light, it will generally react within a few minutes. There are two main signs that a leaf is getting too much light. The most common is that the leaf will "taco" or "canoe" meaning that the edges of the leaf will curl so as to reduce the amount of light hitting the leaf. Another behavior is that the leaf will rotate around the petiole, changing from a horizontal orientation to a more vertical orientation. That action similar to a Venetian blind opening and closing. The result is the same for both behaviors - less leaf area is exposed to the light.

If you see either of those behaviors, or any other unusual physical changes, raise the light 4" which I believe will drop the PPFD at least 100µmol.

The affected leaves should start to turn back to their normal orientation within 30 minutes, though I did have a cola bend under very high light and it never did straighten back out.

800µmol is a decent amount of light. If you feed your plants that amount of light (remember, light is how a plant makes food), cannabis will reward you with a very good crop. Increasing light above 800µmol will get you a larger crop (4-5% per 50µmol though the yield curve rolls off gradually, according to research).

LED grow lights do not generate enough heat to burn leaf tissue but at extreme light levels, you can damage the plant. In my most recent grow, the dimmer switch failed and the light went to 100% power. PPFD went > 1250µmol for an hour or so and it caused that part of the plant to "fox tail".

At 30", your plants may well be getting the very minimum amount of light recommended for a plant in mid-veg or later. That's an educated guess, please understand because I can't find any actual PPFD for your light. You could run the light at that level but your crop yield would be modest.

Not much info on the adjusta 720. It's a six bar light very similar to the Omega black, maxibright varidrive and lumi black led lights. All Chinese.
I think 12" - 30cm and you'll be around 1300 in the centre.
15" - 40cm seems a good distance for flowering.

ab2t2000 said:

Will I still get good results at a foot or so away?

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I use photone and then set the light intensity to the DLI that I want. For height I use the manufacturers recommended height.

Moflow said:

Not much info on the adjusta 720. It's a six bar light very similar to the Omega black, maxibright varidrive and lumi black led lights. All Chinese.
I think 12" - 30cm and you'll be around 1300 in the centre.
15" - 40cm seems a good distance for flowering.
View attachment 5389034View attachment 5389035

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Great find. My numbers were off.

And the numbers on the website that I quoted above are absolutely bullshit, to wit "We've tested these LEDs with an Apogee PAR meter, and the PPFD outputs are around 1000-1200 PPFD across the canopy from 12" which is amazing!"

At 50cm, it's 1k in the middle but more 1' off center and PPFD plummets. The OP going to have a challenge to get an even light cast.

40 cm will be 1100 in the center but lower off center. If one plant, I'd top it and LST it. If more than one plant, place them in a circle around the hot spot in the middle and Bob's your uncle.