UMol lighting chart

[Stone420]

Greetings:

I am setting up a new 2x4 with a HLG 320 XL QB light w/ adjustable dimmer power supply. It can go from 36 watts low to 349 watts maxed...these are at the wall readings.

Can anyone link a chart showing how many uMols to set for seedlings based on a 18 hour veg day? I know I'll increase uMol as they grow, so any chart I can see and print will be helpful. I have a PAR sensor, so I need to know how to find settings for optimal growth in various stages of growth.

THANKS!!

 

[FelipeBlu]

I don’t have a chart, but from my experience, a PPFD of 250 umoles is a reasonable place to start with seedlings that have at least 3 sets of true leaves. Prior to that, even a 26W CFL (2” distance) would be adequate.

 

[Old Salt]

@Emilya has posted Lux figures she's using in her current grow. There is a conversion factor that can be used. It's near 67 Lux/PAR. I think she has the exact value listed.

 

[Elevated Lighting Company]

Greetings:

I am setting up a new 2x4 with a HLG 320 XL QB light w/ adjustable dimmer power supply. It can go from 36 watts low to 349 watts maxed...these are at the wall readings.

Can anyone link a chart showing how many uMols to set for seedlings based on a 18 hour veg day? I know I'll increase uMol as they grow, so any chart I can see and print will be helpful. I have a PAR sensor, so I need to know how to find settings for optimal growth in various stages of growth.

THANKS!!

Your best option is to do what Old Salt mentioned above. Get a LUX meter or download a reasonable one to your phone to measure then convert. It will give you a rough idea where your PPFD is at.

Also note hanging height will impact this as well.

 

[Emilya Green]

Here is what I found as I was publishing the info about my new lights:

We know that clones and seedlings need between 5000-7000 LUX for optimum growth. We know that in Veg the plants can take a lot more light and depending on how big they are, 15k-50K LUX is appropriate for optimum growth. In flower we can hit them with even more light, and 45K-65K LUX will do just fine. Some plants can stand up to 75K LUX in flower, but you are in risky territory of bleaching up here, and generally anything over 85K would be lethal.

With my lights the conversion factor to move to PAR from my lux numbers was 66.8, or 67 as was mentioned above. So converting the above to PAR, we get for seedlings, 75-100 PAR, 225-750 PAR for veg and 670-975 PAR for flower.

 

[Mars Hydro]

Hi Stone420, welcome to
Usually during veg, when you have 200umol , plants will start to grow, they will grow very nice if the ppfd reaches around 400~600umol.
During flower: from 500umol, plants will flower, but they will flower really good around 700~900 umol. Data over 900~1000~2000 actually have not too much difference for plants' growing, so no need to look for too high par value. Hope this helps!

 

[Madtabman]

I just went with this and have tweeked it a little since I started without CO2. some people say go for an average. But myself personally I make these figures a maximum anywhere at canopy level. I'm newish to LEDs but I've already suffered light stress and bleached buds. NEVER AGAIN!

 

[Madtabman]

And something along these lines once flowering. Without added CO2 But I think 1200 at week six is really pushing it. Some scientists have said you never need over 800 without CO2. But I don't have the links or the name of the scientists or the study I'm sorry. It was some Indian sounding scientists in some Indian sounding country

 

[Madtabman]

Found it

How Much Light (PPF) Do You Need for Indoor Cannabis? - Coco For Cannabis

The science of photosynthesis, PAR and PPF for indoor cannabis. Our Grow Space Calculator shows the optimal light and harvest estimates for any grow space.

www.cocoforcannabis.com

 

[Delps8]

The "Indian" scientist was one of the co-authors of a paper that I refer to as the Chandra paper (attached). It was a very helpful paper because it discussed, among other things, the change in net photosynthesis at different temperatures, light levels, and CO2 levels.

And it has nothing to do with the yield of a cannabis crop.

The study measured photosynthesis of leaves where the plants had been grown in varying conditions and the leaves were plucked and their photosynthesis was measured in a chamber about the size of a shoe box.

When I read the paper, I found it interesting but the first question that came to mind was "What if I'm not harvesting net photosynthesis?"

The assumption that many people make is that photosynthesis is a valid proxy for cannabis yield. This issue was specifically addressed in the "Frontiers" paper (attached).

I created the table below from the information in the Frontiers paper. It shows how cannabis dry weight yield increased as PPFD increased. Yes, the curve does roll off, not unexpectedly, and you can add up the percentage increase in yield as light levels increase.

After reading this, and many other papers, my perspective is not "How high should I turn up my lights?" but has become "How much do you want to reduce your yield by not turning up the lights?"

The best presentation that I've seen on how to increase yield was given my Mitch Westmoreland in his You Tube videos from early 2024 where he shares some of the details of the research that he's done for this PhD thesis. He's been studying under the guidance of Dr. Bruce Bugbee and I've read his work going back to 2021. In his 50± mi videos (he's done two videos that cover very similar topics) he touches on the increase in yield by giving your plants a lot of light and he also goes into the impact of high temperatures on cannabinoids.

I'm sure I've read the info from cocoforcannabis and I suspect that his argument is that you only "need" X mols or PPFD. He's probably pretty much in line with Shane @ Migro and many other sites that advocate modest amounts of light. I have yet to see any commercial site that substantiates their advice with research data. Should I take, as gospel, someone who gives me advice because "trust me" or do I read the results of research and draw my own conclusions? I chose the latter.

You can get a really nice crop at 600µmol or 700µmol. No question about it. You will find, however that your plants grow better and that yield will increase if you give your plants more light, assuming that your plants can use the light that you're giving them. And if they can't, they will let you know.

After 3 ½ years being active here and on a few other sites, my observation is that growers lose more of their crop by not giving their plants enough light than they do by giving them too much light.

And the reason for that is that it's almost impossible damage a cannabis plant by giving it too much light but, if you check the chart above, you'll get some idea of how much you're not getting at your current light level.

 

[Delps8]

And something along these lines once flowering. Without added CO2 But I think 1200 at week six is really pushing it. Some scientists have said you never need over 800 without CO2. But I don't have the links or the name of the scientists or the study I'm sorry. It was some Indian sounding scientists in some Indian sounding country

By day 40, generally speaking, my grows are at 900µmol. CO2 is about 420ppm.

Check any of my grow journals for light values. I measure light with an Apogee, pretty much every day and publish the readings.

Overall, if your grow can't tolerate 800-1000µmol, check your grow. Cannabis is a light whore loves light.

 

[Madtabman]

So I can't measure Co2. But I believe it to be around 350. Should I aim for 800 umols?

 

[Madtabman]

By day 40, generally speaking, my grows are at 900µmol. CO2 is about 420ppm.

Check any of my grow journals for light values. I measure light with an Apogee, pretty much every day and publish the readings.

Overall, if your grow can't tolerate 800-1000µmol, check your grow. Cannabis is a light whore loves light.

Thanks for the clearer information. So I can't measure the CO2 but believe it to be around 350ish. Should I aim for a round 800 umols?
And how do you measure your CO2 levels?
And I'm guessing you never go over them 900µmol?

 

[Delps8]

Thanks for the clearer information. So I can't measure the CO2 but believe it to be around 350ish. Should I aim for a round 800 umols?
And how do you measure your CO2 levels?
And I'm guessing you never go over them 900µmol?

Atmospheric CO2 is gradually and the "official" measure is at Manua Loa in Hawaii and it recently measured at 424 PPM. Growers who have their tents in bedroom report that they're seeing 600PPM± .

I got a coupon for the Ace Rite CO2 meter a couple of years ago and it was in the 400 - low 500's range during the day.

350 would be unusually low. Did you measure that in a tent? If that's accurate, that means that you're not getting adequate ventilation and you should fix that ASAP. I say that because, in Mitch Westmoreland's video he says that a slight drop in CO2 can result in a very large reduction in yield.

[found it]

Here's a screen shot from his video:

That's the title of the video - "Crop Steering…". It's the best single source of how to get maximum yield I've seen in three ½ years of reading and watching everything I can get my eyeballs on.

Yeh, it's about a 20% drop if you're at 350'ish.

Re 900 - I don't know where I've found it (perhaps it's in one of the "DeBacco University videos on YT) but I've seen "the light saturation point" for cannabis is described as being 800-1000µmol. The light saturation point is the light level above which a plant can no longer use the incoming photons. Above that level, the plant will react, by "canoeing" or "tacoing" or by rotating the leaf vertically around the petiole in the same way that a Venetian blind closes. If you get that reaction, drop PPFD by 50-100µmol which you can do by raising the light 1" or 2" or by reducing the power setting on the dimmer.

The light saturation point varies for a lot of reasons. I've seen two grows here on 420 where the plants could not handle >500 µmol. After some troubleshooting, both growers hadn't watered their soil just the right way and the soil was hygrophobic. If VPD is out of range, that can impact how well plants process light (as cause nute imbalances).

If things are dress right dress, you should be able to average 900. I think my grows average over that and I include a lot of data points when I sample PPFD.

This is from 3/21/24 and the canopy was very even. I sample from left rear to left front, center rear to center front, etc. so the low values were in the corners and at the very front or back.

Some of my readings are >1100 and no indication of issues.

How high should you take your plants? Hard to say. A light meter tells you how much light your grow light is generating but only your plants can tell you how much light they can use.

The best approach? Get a lux meter (I've recommended the Uni-T but another grower recently sent me a link for the BTMETER lux meter which has a couple of good features for only $6 more than the Uni-T) and increase the light levels on your grow until you get to the light saturation point.

A lot of Most growers turn up the dial very slowly (I have a theory about why) but, from the perspective of the plant, it's "Bring it on". If you're at, say, 600µmol, bump it up to 700 or 800 and see how the plants react. I wouldn't jump to 900 and then leave for the weekend. That's just not wise. But there's no reason not to jump a hundred or two hundred µmol and then check back on the plants in 30 minutes and 60 minutes to see how they're doing. If they're reacting negatively, drop PPFD a bit, wait a few days for the plant to grow a bit more, turn up the light, watch the plants. Lather, rinse, repeat.

I have had a few of instances of too much light. I've had some young plants that were struggling and I turned up the light and pissed one of them off so I turned the dimmer down a bit for a few days. I had a dimmer go on the fritz and that took my light levels from 1050 or so, to 1250. The only way I knew that had happens was that the temp in the tent popped up and I happened to see it on the AC Infinity app. As soon as I walked I the garage, I could tell that something was up. I fixed the dimmer issue and it took a couple of hours for the plants to move back to their normal orientation. That's just part of the process.

Once plants are mature, the light levels will level off and you'll be amazed at how bountiful these plants are. It takes some thought and some attention to detail but the results can be quite something.

 

[Madtabman]

Atmospheric CO2 is gradually and the "official" measure is at Manua Loa in Hawaii and it recently measured at 424 PPM. Growers who have their tents in bedroom report that they're seeing 600PPM± .

I got a coupon for the Ace Rite CO2 meter a couple of years ago and it was in the 400 - low 500's range during the day.

350 would be unusually low. Did you measure that in a tent? If that's accurate, that means that you're not getting adequate ventilation and you should fix that ASAP. I say that because, in Mitch Westmoreland's video he says that a slight drop in CO2 can result in a very large reduction in yield.

[found it]

Here's a screen shot from his video:

That's the title of the video - "Crop Steering…". It's the best single source of how to get maximum yield I've seen in three ½ years of reading and watching everything I can get my eyeballs on.

Yeh, it's about a 20% drop if you're at 350'ish.

Re 900 - I don't know where I've found it (perhaps it's in one of the "DeBacco University videos on YT) but I've seen "the light saturation point" for cannabis is described as being 800-1000µmol. The light saturation point is the light level above which a plant can no longer use the incoming photons. Above that level, the plant will react, by "canoeing" or "tacoing" or by rotating the leaf vertically around the petiole in the same way that a Venetian blind closes. If you get that reaction, drop PPFD by 50-100µmol which you can do by raising the light 1" or 2" or by reducing the power setting on the dimmer.

The light saturation point varies for a lot of reasons. I've seen two grows here on 420 where the plants could not handle >500 µmol. After some troubleshooting, both growers hadn't watered their soil just the right way and the soil was hygrophobic. If VPD is out of range, that can impact how well plants process light (as cause nute imbalances).

If things are dress right dress, you should be able to average 900. I think my grows average over that and I include a lot of data points when I sample PPFD.

This is from 3/21/24 and the canopy was very even. I sample from left rear to left front, center rear to center front, etc. so the low values were in the corners and at the very front or back.

Some of my readings are >1100 and no indication of issues.

How high should you take your plants? Hard to say. A light meter tells you how much light your grow light is generating but only your plants can tell you how much light they can use.

The best approach? Get a lux meter (I've recommended the Uni-T but another grower recently sent me a link for the BTMETER lux meter which has a couple of good features for only $6 more than the Uni-T) and increase the light levels on your grow until you get to the light saturation point.

A lot of Most growers turn up the dial very slowly (I have a theory about why) but, from the perspective of the plant, it's "Bring it on". If you're at, say, 600µmol, bump it up to 700 or 800 and see how the plants react. I wouldn't jump to 900 and then leave for the weekend. That's just not wise. But there's no reason not to jump a hundred or two hundred µmol and then check back on the plants in 30 minutes and 60 minutes to see how they're doing. If they're reacting negatively, drop PPFD a bit, wait a few days for the plant to grow a bit more, turn up the light, watch the plants. Lather, rinse, repeat.

I have had a few of instances of too much light. I've had some young plants that were struggling and I turned up the light and pissed one of them off so I turned the dimmer down a bit for a few days. I had a dimmer go on the fritz and that took my light levels from 1050 or so, to 1250. The only way I knew that had happens was that the temp in the tent popped up and I happened to see it on the AC Infinity app. As soon as I walked I the garage, I could tell that something was up. I fixed the dimmer issue and it took a couple of hours for the plants to move back to their normal orientation. That's just part of the process.

Once plants are mature, the light levels will level off and you'll be amazed at how bountiful these plants are. It takes some thought and some attention to detail but the results can be quite something.

This post is amazing. It's given me the confidence to experiment a little. I upped the umols to 1100 in the centre. I haven't worked an average out yet. I then checked on them every hour on the first day and every few hours on the second day. Just checked in in the third day and they are happy as Larry, no twisting or anything. I'm on day 21 of flowering and would have never attempted anything like this without your input. Thankyou

 

[Madtabman]

Atmospheric CO2 is gradually and the "official" measure is at Manua Loa in Hawaii and it recently measured at 424 PPM. Growers who have their tents in bedroom report that they're seeing 600PPM± .

I got a coupon for the Ace Rite CO2 meter a couple of years ago and it was in the 400 - low 500's range during the day.

350 would be unusually low. Did you measure that in a tent? If that's accurate, that means that you're not getting adequate ventilation and you should fix that ASAP. I say that because, in Mitch Westmoreland's video he says that a slight drop in CO2 can result in a very large reduction in yield.

[found it]

Here's a screen shot from his video:

That's the title of the video - "Crop Steering…". It's the best single source of how to get maximum yield I've seen in three ½ years of reading and watching everything I can get my eyeballs on.

Yeh, it's about a 20% drop if you're at 350'ish.

Re 900 - I don't know where I've found it (perhaps it's in one of the "DeBacco University videos on YT) but I've seen "the light saturation point" for cannabis is described as being 800-1000µmol. The light saturation point is the light level above which a plant can no longer use the incoming photons. Above that level, the plant will react, by "canoeing" or "tacoing" or by rotating the leaf vertically around the petiole in the same way that a Venetian blind closes. If you get that reaction, drop PPFD by 50-100µmol which you can do by raising the light 1" or 2" or by reducing the power setting on the dimmer.

The light saturation point varies for a lot of reasons. I've seen two grows here on 420 where the plants could not handle >500 µmol. After some troubleshooting, both growers hadn't watered their soil just the right way and the soil was hygrophobic. If VPD is out of range, that can impact how well plants process light (as cause nute imbalances).

If things are dress right dress, you should be able to average 900. I think my grows average over that and I include a lot of data points when I sample PPFD.

This is from 3/21/24 and the canopy was very even. I sample from left rear to left front, center rear to center front, etc. so the low values were in the corners and at the very front or back.

Some of my readings are >1100 and no indication of issues.

How high should you take your plants? Hard to say. A light meter tells you how much light your grow light is generating but only your plants can tell you how much light they can use.

The best approach? Get a lux meter (I've recommended the Uni-T but another grower recently sent me a link for the BTMETER lux meter which has a couple of good features for only $6 more than the Uni-T) and increase the light levels on your grow until you get to the light saturation point.

A lot of Most growers turn up the dial very slowly (I have a theory about why) but, from the perspective of the plant, it's "Bring it on". If you're at, say, 600µmol, bump it up to 700 or 800 and see how the plants react. I wouldn't jump to 900 and then leave for the weekend. That's just not wise. But there's no reason not to jump a hundred or two hundred µmol and then check back on the plants in 30 minutes and 60 minutes to see how they're doing. If they're reacting negatively, drop PPFD a bit, wait a few days for the plant to grow a bit more, turn up the light, watch the plants. Lather, rinse, repeat.

I have had a few of instances of too much light. I've had some young plants that were struggling and I turned up the light and pissed one of them off so I turned the dimmer down a bit for a few days. I had a dimmer go on the fritz and that took my light levels from 1050 or so, to 1250. The only way I knew that had happens was that the temp in the tent popped up and I happened to see it on the AC Infinity app. As soon as I walked I the garage, I could tell that something was up. I fixed the dimmer issue and it took a couple of hours for the plants to move back to their normal orientation. That's just part of the process.

Once plants are mature, the light levels will level off and you'll be amazed at how bountiful these plants are. It takes some thought and some attention to detail but the results can be quite something.

 

[Delps8]

This post is amazing. It's given me the confidence to experiment a little. I upped the umols to 1100 in the centre. I haven't worked an average out yet. I then checked on them every hour on the first day and every few hours on the second day. Just checked in in the third day and they are happy as Larry, no twisting or anything. I'm on day 21 of flowering and would have never attempted anything like this without your input. Thankyou

I appreciate your feedback. Thank you.

1100µmol is a lot of light and, in ambient CO2, you're right at "the edge". The fact that your plants can handle that much light tells me that your environment is in good shape. Stay on top of it, though, because you're "playing above the rim" (basketball analogy), so to speak.

How are you measuring PPFD?

Interesting that this is an old thread and that @FelipeBlu contributed a few years back.

When I started growing (the old man starts telling stories!) I had a devil of a time with pH dropping. At the time, I was using what I referred to as "The Wonder Chart", which was adopted here on 420 as a guide for hydro growers. It had a lot of validity but fell down very badly in the advice on what to do about falling pH. According to that document, the proper response was to low EC until pH stabilized. I spent a lot of hours, pumping out the 26 gallons of nutes in my res and, eventually gave up.

The advice is completely wrong. Falling pH is as normal as pH rising and, unless you've got decaying organic matter in the res, it's simply a function of how plants are taking up nutes. I didn't know it at the time and it wasn't until @FelipeBlu sent me a message that I was able to stop pulling out my hair trying to "fix" an expected behavior.

He imparted enough knowledge about nutrients that I stopped using bottled nutes and went to a dry fert. I've had zero signficant issues since he was kind enough to help me and "many thanks" are due if he logs in again.

<storytime/>

The PPFD data I posted previously was from the late stages of a grow. Until I get to "lots" of flower tops, I sample light in a grid fashion, as shown here:

X3=the light
283 is wattage

I find the grid pattern helpful because it represent how the light is falling the different areas of the plant.

Averages are under the "front row" and then the standard deviation is the bottom row. SD is pretty handy and it just a Google away if you're not familiar with it.

Those values tell me that it was a pretty even canopy but, if I was so inclined, I'd raise drop the lower left of the canopy to even it up ("inclined" - no pun intended).


At day 21, your crop is finished building out so, per the information in the Westmoreland videos, you'll want to keep the temps at your flower tops below 78°.

 

[Madtabman]

As I previously mentioned I haven't played with trying to get an average but for now I was just taking note that the highest reading was 1100umols in the centre at the highest bud hight. And saw that all other readings are below that number. I use the photobio meter and hold it right next to the bud. I'm going to attempt doing readings as you have said. I'll do that this evening. My canopy is fairly even but doing 3 different strains and one of them definitely stretched more than the others so that one went a bit crazy and ended up about 4-6 inches taller than the other 3 . It's not bad but I've done better before. And I've just received some orange x mimosa seeds so will be doing all the same strain next time. It will be so level you'll be able to sit at it like its a dining table. I love this hobby. And will always be improving. Especially with the help of you lot. I appreciate it greatly once I get my average reading I'll post it back here. Thanks again

 

[Madtabman]

I appreciate your feedback. Thank you.

1100µmol is a lot of light and, in ambient CO2, you're right at "the edge". The fact that your plants can handle that much light tells me that your environment is in good shape. Stay on top of it, though, because you're "playing above the rim" (basketball analogy), so to speak.

How are you measuring PPFD?

Interesting that this is an old thread and that @FelipeBlu contributed a few years back.

When I started growing (the old man starts telling stories!) I had a devil of a time with pH dropping. At the time, I was using what I referred to as "The Wonder Chart", which was adopted here on 420 as a guide for hydro growers. It had a lot of validity but fell down very badly in the advice on what to do about falling pH. According to that document, the proper response was to low EC until pH stabilized. I spent a lot of hours, pumping out the 26 gallons of nutes in my res and, eventually gave up.

The advice is completely wrong. Falling pH is as normal as pH rising and, unless you've got decaying organic matter in the res, it's simply a function of how plants are taking up nutes. I didn't know it at the time and it wasn't until @FelipeBlu sent me a message that I was able to stop pulling out my hair trying to "fix" an expected behavior.

He imparted enough knowledge about nutrients that I stopped using bottled nutes and went to a dry fert. I've had zero signficant issues since he was kind enough to help me and "many thanks" are due if he logs in again.

<storytime/>

The PPFD data I posted previously was from the late stages of a grow. Until I get to "lots" of flower tops, I sample light in a grid fashion, as shown here:

X3=the light
283 is wattage

I find the grid pattern helpful because it represent how the light is falling the different areas of the plant.

Averages are under the "front row" and then the standard deviation is the bottom row. SD is pretty handy and it just a Google away if you're not familiar with it.

Those values tell me that it was a pretty even canopy but, if I was so inclined, I'd raise drop the lower left of the canopy to even it up ("inclined" - no pun intended).


At day 21, your crop is finished building out so, per the information in the Westmoreland videos, you'll want to keep the temps at your flower tops below 78°.

This is one you might be able to clarify for me @Delps8 You mention no higher than 25c/78f at the bud hight. Ive asked the question a few times. Would this be air temperature or the temperature of the leaf at that height using my laser temp reader? I could never get a straight answer. There was an article i read by smokeyokies that didn't 100 percent answer my question but it steared me to measuring leaf temperature at that height so thats how I base my environment readings. I'm at 27c air temperature-25c leaf temperature and 56 RH puts me at 1.17 kpa.

 

[Madtabman]

This is one you might be able to clarify for me @Delps8 You mention no higher than 25c/78f at the bud hight. Ive asked the question a few times. Would this be air temperature or the temperature of the leaf at that height using my laser temp reader? I could never get a straight answer. There was an article i read by smokeyokies that didn't 100 percent answer my question but it steared me to measuring leaf temperature at that height so thats how I base my environment readings. I'm at 27c air temperature-25c leaf temperature and 56 RH puts me at 1.17 kpa.

I just done my average and although my canopy is definitely not as level as I'd like. It's coming back at 946 umols. The highest reading being 1130 umols and the lowest reading being 700 umols. Im pretty sure I've done my readings correctly and I'm happy with that. I will be keeping my eyes very closely on the highest readings areas for signs of stress. Like a mentioned it wasn't a typical grow for me and I struggled to get a level canopy. I think its a bit late now to do anything about that. But I've learned loads so far on this grow. And I'm nowhere near harvest yet