PAR DLI

[Jimi O'Connor]

So I just got a light meter. Long story short according to the meter, my light wasn't on a high enough power setting. It was at 40% power. When using the meter it's suggesting I should turn it to 80% power. I'm wondering if that's to big a jump and will hurt the plant.

The plants in the 2nd week of flower

The DLI is around 20 and the PAR was around 600.

That's if I follow the meter and increase the power to 70 % or 80%.

70% still is a little low on some spots of the plant. 80% seems to check most all of the boxes.

I guess my question is if I increase the power from 4 to 8 is that going to mess up the plant?

 

[twentyeight.threefive]

So I just got a light meter. Long story short according to the meter, my light wasn't on a high enough power setting. It was at 40% power. When using the meter it's suggesting I should turn it to 80% power. I'm wondering if that's to big a jump and will hurt the plant.

The plants in the 2nd week of flower

The DLI is around 20 and the PAR was around 600.

That's if I follow the meter and increase the power to 70 % or 80%.

70% still is a little low on some spots of the plant. 80% seems to check most all of the boxes.

I guess my question is if I increase the power from 4 to 8 is that going to mess up the plant?

Doubling the light output instantly is going to stress the plant. I'd suggest slowly increasing the light output. Like one setting a week or something like that.

 

[Delps8]

Congrats on buying a light meter and putting it to good use. I've littered the pages of RIU and other sites urging growers to take that step because it's the easiest way to get healthy plants and high quality crops.

DLI of 20 mol is very low but there's no reason to not increase DLI very rapidly. Bruce Bugbee addressed this issue, specifically, in YouTube interview that he did with Dr. GrowIt, if I recall correctly. The question posed used that particular value - 600µmol. The answer was simple and unequivocal - take it to 800µmol and see how the plants react. If they don't show signs of too much light (tacoing or rotating leaves around the petiole so as to reduce the area exposed to light), then raise them again the next day.

There's no magic to this but the key point is not if cannabis can handle the increased light level (I routinely grow my autos at 80 DLI and my photos at >1100µmol) but how well grow environment + your plants are able to handle the new light levels. Some strains can only tolerate 800 under the best of conditions but I have seen two grows where plants can't tolerate > 500µmol. The reason for both of those grows was that the growers hadn't watered their plants correctly and the soil was hygrophobic. Assuming that your grow is in good shape, there's no reason why you should be able to feed your plants at the 1k level.

If you go from 600 to 800 and don't see any negative reaction, I would next jump to 900µmol. That's right in the middle of what the 800-1000 range which is generally used to describe the light saturation point.

Once you bump to 900, check to see how your plants react and, if everything looks good, go to 1k. Assuming that your plants react positively, there's simply no reason to not give them that level of light.

Again, you should be able to jump 200µmol the first day and then another hundred or two in the next day. Cannabis thrives on high light and it's absolutely clear that crop quality and quality (the ratio of the mass of flower to above ground mass) increase as light levels increase.

 

[Jimi O'Connor]

Congrats on buying a light meter and putting it to good use. I've littered the pages of RIU and other sites urging growers to take that step because it's the easiest way to get healthy plants and high quality crops.

DLI of 20 mol is very low but there's no reason to not increase DLI very rapidly. Bruce Bugbee addressed this issue, specifically, in YouTube interview that he did with Dr. GrowIt, if I recall correctly. The question posed used that particular value - 600µmol. The answer was simple and unequivocal - take it to 800µmol and see how the plants react. If they don't show signs of too much light (tacoing or rotating leaves around the petiole so as to reduce the area exposed to light), then raise them again the next day.

There's no magic to this but the key point is not if cannabis can handle the increased light level (I routinely grow my autos at 80 DLI and my photos at >1100µmol) but how well grow environment + your plants are able to handle the new light levels. Some strains can only tolerate 800 under the best of conditions but I have seen two grows where plants can't tolerate > 500µmol. The reason for both of those grows was that the growers hadn't watered their plants correctly and the soil was hygrophobic. Assuming that your grow is in good shape, there's no reason why you should be able to feed your plants at the 1k level.

If you go from 600 to 800 and don't see any negative reaction, I would next jump to 900µmol. That's right in the middle of what the 800-1000 range which is generally used to describe the light saturation point.

Once you bump to 900, check to see how your plants react and, if everything looks good, go to 1k. Assuming that your plants react positively, there's simply no reason to not give them that level of light.

Again, you should be able to jump 200µmol the first day and then another hundred or two in the next day. Cannabis thrives on high light and it's absolutely clear that crop quality and quality (the ratio of the mass of flower to above ground mass) increase as light levels increase.

What is umol?

And is this a sign the plants have to much light?

 

[Moflow]

What is umol?

And is this a sign the plants have to much light?

Micro moles (µmol) Oversimplified

Here's a handy umol to dli calculator

Daily Light Integral (DLI) Calculator | Waveform Lighting

With a PPFD input value and total hours of use per day, Daily Light Integral (DLI) values can be calculated using our online calculator.

www.waveformlighting.com

 

[Moflow]

What light meter did you end up getting?

 

[Delps8]

What is umol?

And is this a sign the plants have to much light?

Per @Moflow it's a micro mol. DLI ("daily light integral" = how much light is falling on a plant in a day) is expressed in mol but PPFD (how much light is falling on a square meter every second) is expressed in µmol. On macOS, µ is option m. You can type is in windows as Alt+0230.

I'm a hydro grower so we drown our plants but I think that plants like that in soil are getting too much water or it could be early stage of N toxicity. I would describe them a "clawing down" and I think those are two factors that can result in leaves taking that shape.

Too much light is very different - leaves will "taco" or "canoe" or they can rotate around their petiole in the same way that a Venetian blind changes from level to vertical-ish. I also bent a cola a couple of years back.

If plants get too much light, they'll react pretty quickly. I've had two instances where my light maxed out, once was my error, the other was when a dimmer went on the fritz. In both cases, the leaves started curling within a few minutes. Fortunately, I caught the problem after about 30 minutes, in both cases. I got things un-f'd very quickly and it took…30-60 minutes for the leaves to rotate back to their normal orientation. In the case of the cola that bent, it stayed bent.

It is hard to damage a plant with an LED. HPS is a different story because that's too much heat that causes physical destruction of plant tissue. When an LED is turned up too high it's, in almost all cases, that the plant is getting too many photons and can't process them (photosynthesis) quickly enough so it starts turning away. But it is energy so if I hadn't turned down the dimmer, there could have been some plant damage.

It's really hard to damage a plant using an LED. I've seen pictures of plants growing into the light bars and they didn't get heat damaged but it took a while for them to recover from too many photons.


Oh, yeh, if plants aren't getting watered correctly (I think it's too much water, in your case) - I've seen two grows that couldn't handle >500µmol. In both cases, one here and one on another site, the soil was "hygrophobic" and the plant was really struggling at just 500.


I've added a DLI chart for a photo grow from early 2023.
View attachment 5408582

 

[Delps8]

Doubling the light output instantly is going to stress the plant. I'd suggest slowly increasing the light output. Like one setting a week or something like that.

There's nothing wrong with that approach.

A lot of growers are quite happy with getting "two to four ounces" out of their plants. If that's what people are shooting for, increasing light levels by 10% a week will help ensure that they don't exceed their expectations.

 

[twentyeight.threefive]

There's nothing wrong with that approach.

A lot of growers are quite happy with getting "two to four ounces" out of their plants. If that's what people are shooting for, increasing light levels by 10% a week will help ensure that they don't exceed their expectations.

There are many more factors into a plant only producing 2-4 oz. than someone doubling their light weeks into flower. Doubling the light output is more likely to stress the plant and cause harm than it is to help the plant produce drastically more flower…

 

[Delps8]

There are many more factors into a plant only producing 2-4 oz. than someone doubling their light weeks into flower.

I'm really not clear on the point that you're trying to make. There are a lot of factors in the grow environment, no doubt about it.

"Doubling the light output is more likely to stress the plant and cause harm than it is to help the plant produce drastically more flower…"
Without specifics, it's impossible to agree or disagree. My interest in chasing down the rabbit hole is limited so I think the closest I can get it to staying involved in this is that in some cases a grow will do just fine, in others it won't do very well.

Growers should monitor their plants and see how they react. It's that simple.

 

[Budzbuddha]

Light stress is a known plant stressor - too much can cause reactive processes within plant , such as Photoinhibition.

Just as one would over feed a plant - the plant will show negative reactions . Environmental stressors with VPD can also affect plants.
Light Stress is much more than bleaching . Photoinhibition is a reduction in a plant's (or other photosynthetic organism's) capacity for photosynthesis caused by exposure to strong light (above the saturation point). Photoinhibition is not caused by high light per se, but rather absorption of too much light energy compared with the photosynthetic capacity, i.e. any excess energy that the photosystem cannot handle is damaging.

Even tho I build rigs with high output - I never throw plants under max power. I always look for a happy medium - either by measuring acceptable DLI / PAR levels at canopy level. No need to go balls to the wall - besides it shortens the life span of your lights. I usually look / monitor responses to my initial settings based on distance of canopy to light. Usually an 18”to 20” distance for a baseline. Just as you would control power over seedlings , you adjust , plain and simple. Max power over seedlings for example would torch them. Regardless if you did everything else right.

I basically look for at least a lateral leaf response , flat to light per se. I defol them too , to punch light deeper without mashing the gas and wrecking the tops. Too much light on buds - for example - can mutate the flower tops and look like clubbed feet.

Red stems are among many other things that will begin to manifest.

This is all avoidable. With control.

 

[twentyeight.threefive]

I'm really not clear on the point that you're trying to make. There are a lot of factors in the grow environment, no doubt about it.

"Doubling the light output is more likely to stress the plant and cause harm than it is to help the plant produce drastically more flower…"
Without specifics, it's impossible to agree or disagree. My interest in chasing down the rabbit hole is limited so I think the closest I can get it to staying involved in this is that in some cases a grow will do just fine, in others it won't do very well.

Growers should monitor their plants and see how they react. It's that simple.

I mean I thought the point was clear. The idea of the OP to just double his light setting is a bad idea.

Edit: My mistake it was the OP talking about doubling the light, not you Delps8

It’s more likely to cause issues with the plant rather than immediately help the plant flower to it’s max potential. You don’t need specific numbers to come to this conclusion.