How far should the LED plant growth lamp be from the plant?

[Anny Tang]

Where should the growth lamp be placed?
For seedlings, LED grow lights should usually be installed between 24-36 inches above the plant canopy-however, this depends on the power (wattage) of the light source. Place the LED planting light farthest away from the seedlings (~36 inches)-this keeps the heat and light intensity low and helps prevent the seedlings from drying out. Once the root system is established and begins to sprout, the light can be moved closer (usually within the first 2-3 weeks).
During the plant growth stage, the LED planting light should be 12-24 inches from the top of the canopy. At this stage, photosynthesis requires more light, so the light source should be located near the plant.
As the plant enters the flowering period, the need for strong light decreases. The top leaves of the canopy should be 18-24 inches from the light source to produce flowers. It is at this stage that the height of the plant increases and the fruit grows. Depending on the light and how you want your crops to grow, you don’t have to change the height of the light during the flowering process, especially when you don’t want tall plants.
How far should the LED planting light be from the seedling?
In the early stages of growth, seedlings are fragile and require less light. This means that you don't want to increase the strength too early, because the seedlings will reproduce in a gentler way. Depending on the size of the light, the growing light can be safely held somewhere between 24 and 36 inches from the top of the soil.
How far should LED plant growth lights be used?
As plants grow, their needs change. After the vegetative stage is complete, the plant enters the flowering or "flowering" stage. For mature factories, they have become necessary places to thrive. During the flowering stage, LED planting lights should be located between 16 and 36 inches from the plant canopy. Moving the growing light closer increases the light intensity, thus maximizing photosynthesis. However, if the growth lights are too close to the top of the plant, they may cause the growth area to expand, spread and even damage the plant.

 

[Narsbars]

Height from the top should be judged using PAR. Using 36 inches would mean you had to have a huge amount of LEDs.
I have a P1500 and the general distance is 14 inches in a 2x2 area. I researched the PAR maps and got what I felt was the most accurate from the manufacturer and independent review sites.

 

[Paul Squiggle]

Height from the top should be judged using PAR. Using 36 inches would mean you had to have a huge amount of LEDs.
I have a P1500 and the general distance is 14 inches in a 2x2 area. I researched the PAR maps and got what I felt was the most accurate from the manufacturer and independent review sites.

none of the manufacturers recommendations worked for me.
I go the simple root.
If they stretch, it's to far away
If they burn or bleach, it's to close

 

[Narsbars]

I like the KISS principle, but need a little more knowledge.

 

[SmokingWings]

none of the manufacturers recommendations worked for me.
I go the simple root.
If they stretch, it's to far away
If they burn or bleach, it's to close

Sounds right and as simple as can be.

The more science minded will also study the angle of the reflector.

 

[Bobby Blunt]

I have been growing for a few years using MH and HPS lighting with good success, this is my first LED grow. I have 2 Green Go LED lights a 1000w for my 2'x2'x5' and a 1200w for my 4'x'4x7', I started this grow, 3/9/21 auto flowers Sour Diesel and a auto Glue Berry OG in the 2'x2' I set the light a 33" from the top of the plants, the sour diesel to me was stretching too quickly, which could mean not enough light, I've dropped down to 27" to the tops and keeping an eye on them. I view all growing articles as starting points, I set up as they suggest and watch to see how my plants react if they're fine I'm fine, if not I make adjustments to get them right. There are so many variables with growing the cannabis plant read, study, and grow. This is sturdy plant you really have screw up to kill it, don't be afraid to work with it, just remember, adjust a little bit at a time.

 

[Darknstormy82]

You can get them pretty close to an LED but a sure sign you're to close is foxtails.

 

[Mayne]

I have been growing for a few years using MH and HPS lighting with good success, this is my first LED grow. I have 2 Green Go LED lights a 1000w for my 2'x2'x5' and a 1200w for my 4'x'4x7', I started this grow, 3/9/21 auto flowers Sour Diesel and a auto Glue Berry OG in the 2'x2' I set the light a 33" from the top of the plants, the sour diesel to me was stretching too quickly, which could mean not enough light, I've dropped down to 27" to the tops and keeping an eye on them. I view all growing articles as starting points, I set up as they suggest and watch to see how my plants react if they're fine I'm fine, if not I make adjustments to get them right. There are so many variables with growing the cannabis plant read, study, and grow. This is sturdy plant you really have screw up to kill it, don't be afraid to work with it, just remember, adjust a little bit at a time.

could be genetics also to cause the stretch.

 

[Mayne]

good rule of thumb.

Turn light all the way up. find the sweet spot for flower. 600-900 PAR, or around 50,000 LUX.

Seedlings, 200 par, or around 11,500 Lux.
Every 5 days, raise par by 50,,, :Tip-- They LOVE relax time, or, reduction of light mid day, like cloud cover for 2 hours. They dont need alot of light, so low levels they really enjoy,
Your peak Veg intensity should be about half of your wattage you light is using. By mid Flower, is when you give it all she got. ( light )

You will NEVER have burnt or curled leafs if you follow this.

 

[Mars Hydro]

Recommended Hanging Distance Above Plants

Germination: 24" Seedling: 24"-30" Veg: 18"-24" Flower: 12"-18"

 

[SmokingWings]

could be genetics also to cause the stretch.

True but stretch because of low light has its own unique look; almost looking unhealthy and often the stems cannot support the new growth. Plants that stretch more than others because of genetics still look healthy and stand strong.

 

[Mayne]

red spectrum also causes stretch,

 

[Bobby Blunt]

Thanks guy's for your input, I have been totally frustrated all day with the "Green Go" 1000W in my 2'x2', temp. would go to 72deg's, RH would be at 39-40% with a humidifier in the tent, I swapped out the 1000W "Green Go" for the 1200W into my 2'x2' the change was like day and night, 72deg's/RH 46% with a humidifier in the tent, leaves are reaching are up to the top of the light like they should, plants are 17" from the light but the difference I see is the light spectrum in the 1200W light is throwing more light/heat and the plants are responding to it. Checked on the plants around 2am, lights and humidifier off, 18hr timer, temp is 68deg./RH 51% I never had to go through this with my HID or CFL system's, CFL's in the 2'x2'; 1x 250W + 2x 23w with great results. I understand and see how LED's are impacting the Marijuana industry, I just don't have the patience to tinker with or invest any more time into something that's still evolving but I will keep reading and researching. "Always seek the knowledge."

 

[SmokingWings]

red spectrum also causes stretch,

As in the stretch when putting the plant into flower. That stretch does not cause unusually thin stems and cause the tops of the plants to fall over. Eventually the colas might fall over towards the end but that looks different than stretch from not enough light. Think along the lines of the photos of someone's new seedling that is 4 inches tall and and has to be held up by a toothpick or some other stick. The plant still has not started to grow the first true leaves and is falling over but does not have any disease.

 

[Mayne]

As in the stretch when putting the plant into flower. That stretch does not cause unusually thin stems and cause the tops of the plants to fall over. Eventually the colas might fall over towards the end but that looks different than stretch from not enough light. Think along the lines of the photos of someone's new seedling that is 4 inches tall and and has to be held up by a toothpick or some other stick. The plant still has not started to grow the first true leaves and is falling over but does not have any disease.

right on man,

 

[Bobby Blunt]

Update from my 3/24/21 post on RH with my Green-go1200w LED light in my 2'x2' tent now that I have both veg and bloom, lights on, temp is 77 and RH is 42% plants are healthy and starting to bloom, germinated a few more seed's for my 4'x4' tent, I'm running a HID system with two balladists a 400w for the MH/veg and a 600W for the HPS/flower they're set up on a peg board behind the tent, unplug and plug and just change the bulb too easy right know the 400w is at 75% power, temp is 75 and RH is 50%, this is day 4 and the little ladies are coming right along. I'm glad I tried the LED but it's not for me. When I finish the grow I'm going back to my CFL's in my 2'x2' a 250w/65k-veg and a 250w/27k-flower I only put 2 plants in and they produce !! Like I said I'm a small home grower and LED's are just too much work, I can trade off the extra heat why they made exhaust fans Good grow everyone, toke on