How much light (PAR) before problems?

[phxazcraig]

I've got a grow where I don't have enough distance from light to canopy to evenly light the canopy. (12 inches in a 4x4 under a 600w HLG LED).

What's a reasonable upper limit to use to not damage the flowers directly under the light? I have over 1300 PAR right now, and over 500 in the corners. I like the corners, but am I going to scorch the center? So far the plants seem fine, but they have just (I hope) finished flower stretch so haven't been in this light intensity for more than a few days.

I'm growing Sour Diesel from seed in coco coir with 5x daily feedings. They are finishing week 4 since flipping to 12/12. Temp is well-controlled at 77-79F, humidity between 53 and 59% RH. Lots of air flow through the tent with power input duct at bottom and 6-inch inline exhaust fan at top.

 

[Pushrod Monkey]

If not using CO2 basically anything exceeding 800 is wasted. As far as too much? Noticing any bleaching or other weirdness at the tops?

 

[jguit]

I try to average out my ppfd over the canopy. Some tops might get a little more than i would like but i try to keep everything in the 700 - 900 range in flower without CO2.

I accidentally hit the canopy on one of my grows in flower with around 1250 ppfd and the plants looked fine, until they didn't.. Took quite a while to notice since the plants were a pretty decent size.

 

[phxazcraig]

I try to average out my ppfd over the canopy. Some tops might get a little more than i would like but i try to keep everything in the 700 - 900 range in flower without CO2.

I accidentally hit the canopy on one of my grows in flower with around 1250 ppfd and the plants looked fine, until they didn't.. Took quite a while to notice since the plants were a pretty decent size.

In my first grow I cooked some autos pretty good before I got a PAR meter. I can set a maximum anywhere I want, but it's going to cost me in the corners. My plan is to be a little too hot in the center and a little too cool in the corners. Need to find the best balance, and that depends on knowing just how bright is too bright. Then I'll make it 'a little too bright'. 1000 PAR in the center seems safe, but the edges...

For sure here I want to know the very earliest signs of 'too much'. I think that will be leaf behavior, curling edges and/or pointing up (praying?)

 

[jguit]

I didnt see any curling edges or tacoing. What i saw were unexplained deficiencies/burns seemingly overnight.

Leaves pointing up (praying) is good. Curling edges, tacoing, unexplained deficiencies (cal/mag usually) and bleaching is bad.

 

[freezeland2]

I've got a grow where I don't have enough distance from light to canopy to evenly light the canopy. (12 inches in a 4x4 under a 600w HLG LED).

What's a reasonable upper limit to use to not damage the flowers directly under the light? I have over 1300 PAR right now, and over 500 in the corners. I like the corners, but am I going to scorch the center? So far the plants seem fine, but they have just (I hope) finished flower stretch so haven't been in this light intensity for more than a few days.

I'm growing Sour Diesel from seed in coco coir with 5x daily feedings. They are finishing week 4 since flipping to 12/12. Temp is well-controlled at 77-79F, humidity between 53 and 59% RH. Lots of air flow through the tent with power input duct at bottom and 6-inch inline exhaust fan at top.

I’m running the hlg scorpion. Got 850ish at tops and 625 at edges. Tops are 18 - 24” from light. UVA on them too.

 

[steamroller]

I didnt see any curling edges or tacoing. What i saw were unexplained deficiencies/burns seemingly overnight.

Leaves pointing up (praying) is good. Curling edges, tacoing, unexplained deficiencies (cal/mag usually) and bleaching is bad.

I sure don't know for too powerful lights . I am just a poor Mars owner .
I would think VPD may have had an effect along PAR but I can't say for sure . Thinking leaf temp in particular ?
My TSL 2000 are at 100% about 14-16 inches from canopy at 750 PAR .

 

[phxazcraig]

I’m running the hlg scorpion. Got 850ish at tops and 625 at edges. Tops are 18 - 24” from light. UVA on them too.

A week ago I had 27 inches to play with, and about the same PAR readings.

Today I have 12 inches of clearance left, and not so many options. 1300 in the center, enough at the corners, but coverage is dropping by the day as the plants grow taller and fill out.

 

[freezeland2]

A week ago I had 27 inches to play with, and about the same PAR readings.

Today I have 12 inches of clearance left, and not so many options. 1300 in the center, enough at the corners, but coverage is dropping by the day as the plants grow taller and fill out.

Isn’t that light dimmable?

 

[phxazcraig]

Isn’t that light dimmable?

Of course it is. What happens to the edge coverage then?

 

[steamroller]

I am a big fan of HLG and the Diablo but there is merit in bar light over boards .
This would be one of those times IMO .

 

[freezeland2]

Of course it is. What happens to the edge coverage then?

Well it will go down in PAR obviously. Have you checked to see by how much? You leave it where it’s at and you’ll end with crispy buds.

 

[freezeland2]

I am a big fan of HLG and the Diablo but there is merit in bar light over boards .
This would be one of those times IMO .

My room ceiling is high enough to get through stretch without light distance ever becoming an issue. Room is only like 4 ft wide and with that scorpion in the ceiling I haven’t ever had to lower it. Just use the intensity dial. I have never had it up all the way at full power.

 

[phxazcraig]

Well it will go down in PAR obviously. Have you checked to see by how much? You leave it where it’s at and you’ll end with crispy buds.

I'm at around 12 inches now, which is just barely enough coverage. Consider what happens if the light is so close to the canopy that 6 inches on each side is basically unlit. That turns a 4x4 tent into a 3x3.

I'm trying to learn what might be the earliest signs of overexposure in the hopes of skimming that edge in the middle to maximize growth overall. To date, the plants look good, happy even right underneath. New growth is finally sugar leaves and pistils instead of fan leaves and stalks. But several branches shot up another few inches - those I've bent 90 degrees to at least slow them up a bit. Seems to be working so far. I'm fortunate that one whole plant stretched less than the others and presents a fairly even canopy. It's also the one in the least-accessible corner so has some undergrowth I'd like to defoliate but can't.

I'll remeasure PAR at various points again tonight and see how it's going. I've let the branches around the edges grow high since they get less light anyway. Left more fan leaves on them too.

I do think it is a good argument for bar style lighting that can be spread more.

 

[phxazcraig]

I checked the top of the canopy carefully tonight. Because of the tight spacing there is considerable dropoff from center to corner. But a lot of the center is actually a bit short anyway. (There is no center plant in this group of four.) That helps a lot because most of the brightest area is 2-3 inches below the rest. I see up to 1300 PAR on a couple of the tallest buds near the center, but the bulk of the plants are only seeing 1100-1000. Off center (out from 2x2?) PAR drops to 600 at the edges and 400 in far corners, which isn't bad. So far the center buds look good, and I'm keeping a close eye there. The buds are filling very well - should be large. Ideal conditions at 79F and 53% RH. I'm inclined to leave things alone unless/until I see signs of stress. FIngers crossed.

 

[phxazcraig]

Something else. Only one corner of each plant is under the brightest light. The center of each is under about PAR 800, and two sides less than that.

 

[dbrzz]

I've got a grow where I don't have enough distance from light to canopy to evenly light the canopy. (12 inches in a 4x4 under a 600w HLG LED).

What's a reasonable upper limit to use to not damage the flowers directly under the light? I have over 1300 PAR right now, and over 500 in the corners. I like the corners, but am I going to scorch the center? So far the plants seem fine, but they have just (I hope) finished flower stretch so haven't been in this light intensity for more than a few days.

I'm growing Sour Diesel from seed in coco coir with 5x daily feedings. They are finishing week 4 since flipping to 12/12. Temp is well-controlled at 77-79F, humidity between 53 and 59% RH. Lots of air flow through the tent with power input duct at bottom and 6-inch inline exhaust fan at top.

750 is good average for hybrids

 

[royfree2grow]

Imo PAR isnt the right tool to determine light intensity the plant's is actually getting because it measures the energy of the light source and not the amount of photons flux density used for photosintisys. So if you rely on PAR measurments you dont really know the amunt of mm your plants are getting. If your talking about ppfd which is the most accurate tool for measuring the amount of light used by your plants, i dont think theres an ideal number because it depends on other factors that enables the plant to use these photons for higher rates of photositisys and transpiration i.e environmental factors, water uptake, nutrients and co2.

If you have all other factors supporting these higher rates of PS in theory there is no ceiling and I think the right question here is how much ppfd is required to achive the best weight without lowering quality.

To be honest, proffessional growers that are pulling less than 75g of premium per sq ft are not achieving their potential. If they are getting 85g and higher, theyre doing a good job.

Its obviously strain related but Ime I found that the range of 100g per sq is starting to affect quality but i know there are growers that constantly getting bigger weights and still producing fire so there is always where to look up to.

To get to the big boys league, you have to apply the the greatest amount of light your plants can handle. For my best results ive apllied 1200-1400 ppfd.

 

[pop22]

I've got a grow where I don't have enough distance from light to canopy to evenly light the canopy. (12 inches in a 4x4 under a 600w HLG LED).

What's a reasonable upper limit to use to not damage the flowers directly under the light? I have over 1300 PAR right now, and over 500 in the corners. I like the corners, but am I going to scorch the center? So far the plants seem fine, but they have just (I hope) finished flower stretch so haven't been in this light intensity for more than a few days.

I'm growing Sour Diesel from seed in coco coir with 5x daily feedings. They are finishing week 4 since flipping to 12/12. Temp is well-controlled at 77-79F, humidity between 53 and 59% RH. Lots of air flow through the tent with power input duct at bottom and 6-inch inline exhaust fan at top.

Without CO2 enhancement, you'll start to see light burn around 1200-1300 PPF. You want yourPPFD to be in the 700-900 range. Above 1000 PPFD your plant start using light avoidance mechanisms without additional CO2. If you have a meter or an app to measure PPF, use that to adjust your light via dimming.

 

[rolandrog]

I sure don't know for too powerful lights . I am just a poor Mars owner .
I would think VPD may have had an effect along PAR but I can't say for sure . Thinking leaf temp in particular ?
My TSL 2000 are at 100% about 14-16 inches from canopy at 750 PAR .

How old are your LED lights? I have four Mars SP-3000 LEDs and keep it at 14 inches too :-). My PAR is about 1200 on top. LED lights are suppose to weaken over time. I only had mine for 6 months now and the SP-3000s are operating very well.

I adjust my LED Light distance according to the max temperature I want. In the winter, on cold days, I lower my LED to 8 inches LOL, when I can maintain temps lower than 84F. I am growing sativas.
FYI, the summer sun on a clear day at noon emits over 2,000 PAR. I maximize my top PAR so that the light has a little better chance to penetrate to the lower branches.