DLI, VPD , backing off the LEDs in flower, wtf!

[Homebrew420]

I've just been playing around with a DLI calculator as I go through veg. Seeing what it's saying for my coming weeks and tbh it's left me thinking wft

I've grown before (3x3 tent. 125w cfl for seedlings, then straight into 600w MH veg, 600w hps flower, then back to the MH for the last week or so.. keep humidity and temps in check, full power on the lights and that's it.

Anyway, this time things have advanced a lot since then it seems.
VPD, DLI, LED lights.
Anyway, I've been trying g to keep my VPD in check and seems good, but I've been looking at this DLI stuff.. up coming weeks ramping up all the way to flower, then bam.. drop the DLI again for the first week of flower as if it were 2nd week of veg.. wtaf?

Is this the best method? If I'm strict with the DLI recommendations on the site I'm looking at I may never crank the light up all the way which seems strange and pointless.. if back in The day a 600w hps was better than a 400w, then why not use the light to it's full potential?


What are peoples views on this please

 

[Homebrew420]

For reference,
The website I've been looking at is:
Photone - Grow Light Meter

And my set up now is:
4 x 4 tent
6" extraction
Circulating fan.
Heater (not needed atm)
Ac infinity humidifier
Phlizon FD6000 led light.

 

[bluter]

all of that vpd / dli nonsense works within a broad range and is mostly used in support of marketing more junk.
if you know what you are doing as an experienced grower it's not that useful. if you are a newer grower you could incorporate it if you want.

no one i know locally pays it any attention to it at all. certainly not the best growers. you'll see it used more with internet growers than anything.

 

[OGpapa]

All growers need to know what the plant they're growing is capable of handling.

Not all plants like lights at 12" and 100%> for 18 hours.

These are tools to simply help you determine if what your doing is good or bad.


Too much or too little DLI will give you issues depending on the plants ACTUAL needs.

DLI greatly affects plant growth and development, and the measurement of DLI is important to many gardeners and growers. DLI can be measured, and its measurement is particularly important to commercial farmers and gardeners.

The same thing with VPD.

While a seasonal grower who doesn't follow any guidelines, might be able to figure out where or what to do next. Other growers online or in town are paying attention to what the plant needs to grow.


So if you feel compelled, do some homework. Check out your plants. You will be the true judge of if it works, or not.

 

[Wastei]

As a general rule don't use more light than necessary in the different stages of growth. Excess light will only stress the plant out and slow down growth rates. More is not better!

Chasing high light intensity in veg is pointless. The plant needs different light intensities throughout the grow cycle for optimal growth. In early flower there's very little reason to push high DLI but in mid-later flower the plant can make better use of the higher light intensity.

Use different light intensities to create desired growth. A light stressed plant in veg will show things like miniaturization of the leaves and new shoots, leaves steering away from the light source and excess shoot forming. In severe cases you'll see light bleaching in both veg and flower.

Many new growers focus on pushing high DLI, light intensities and numbers and blindly ignore the plant response.

 

[Delps8]

I've just been playing around with a DLI calculator as I go through veg. Seeing what it's saying for my coming weeks and tbh it's left me thinking wft

I've grown before (3x3 tent. 125w cfl for seedlings, then straight into 600w MH veg, 600w hps flower, then back to the MH for the last week or so.. keep humidity and temps in check, full power on the lights and that's it.

Yup, that approach used blue heavy lights in veg to shape plants - to make them short and compact with lots of foliage. HPS has a lot to red photons which are cheap to generate, in terms of electrical input.

When I started growing in 2021, I followed that pattern and bought a veg LED grow light and a flower LED grow light because I wanted to use the characteristics of those two spectra.

Re. "full power" - as long as light is the limiting factor, turn it up. Research shows that cannabis will grow in ambient CO2 at light levels up to 2000µmol (one trial stopped at 1800, the other researchers stopped at 2000µmol). That's a huge amount of light but, in both cases, the researchers documented that crop yield and crop quality increased in an almost linear manner up to those light levels.

One of the papers are attached. The other source is Mitch Westmoreland who did his PhD thesis on cannabis. The video is available here -

Anyway, this time things have advanced a lot since then it seems.
VPD, DLI, LED lights.
Anyway, I've been trying g to keep my VPD in check and seems good, but I've been looking at this DLI stuff.. up coming weeks ramping up all the way to flower, then bam.. drop the DLI again for the first week of flower as if it were 2nd week of veg.. wtaf?

If you're referring to the graphic on growlightmeter.com (GLM), I've traded email with the programmer (I've been a software engineer for > 30 years) and I asked him for research to back up the graphic. He told me that any citations would be at the bottom of each page. There were none and, as a result, I have no basis to believe that those recommendations "need" to be followed. Without question, you will get a good crop but research indicates that yield and quality increase as light levels increase so there's no particular reason to not provide your plants with as much light as they can handle.

And that's the key point - some grows can only handle, say, 400µmol. I've seen that in two situations and, in both cases, the plants were grown in soil and, due to the watering practices of the growers, the soil was hygrophobic and could not tolerate that very modest level of light.

My approach is to get plants to their light saturation point as soon as possible. My grows max out at about 1150µmol. I use an Apogee PAR meter and sample light on the canopy, sampling just a few points when the plant in early veg, then switching to nine points in a grid fashion and when the bugs pop up in flower, I'll sample the buds so there will be 10 to 18 data points. The data are available in my grow journals.

Re. VPD - VPD is nothing esoteric. It's basically "feels like" temperature for plants. You can grow a plant in a wide variety of combinations of temperature ad humidity and it will survive. Research shows that cannabis grows well at a VPD of 0.8 while germinating, 1.0 in veg, and 1.2-1.5 in flower.

This graphic is for runners (long distance running is a hobby of mine). In the same way that plants respond to different values to temperature + RH, humans are able to perform better under certain conditions. The recent Olympic Trials were held in Florida and the organizers wanted to start the marathon at mid-day. That's nuts. The best running conditions are moderate RH and temps in the 50's. Raising those values to 70° and 70% ensures that you're in for a slog. It's not magic and it's not mystery, it's just how mammals function - we need to be able to throw off heat in order to survive.

Plants are similar - in high temp + low RH, plants have to take in a lot of water to cool off. When those values are very high (when VPD is very high), that will tend to lead to nutrient imbalances.

When VPD is too low, plants can't take up water because they can't transpire it out and, as a result, plants will tend to have problems when VPD is too low.

Back to VPD - there's no requirement to keep cannabis in those ranges but a plant grown in those VPD ranges will tend to grow better than if they're not in those ranges because that's how plants work.

Same thing with light - cannabis will grow in light as low as 64µmol (I've only found one reference to that but one study, the Chandra paper, indicates that value) so you can grow your plants in a light range between 64µmol and 1800 to 2000µmol (assuming light is the limiting factor). The closer your grow is to the VPD ranges and the more light you give the plant, the better it will be able to reach its genetic potential.

Or not.

There's no requirement to put your light at 30" or 12" we know that light is the only way that plants make food. With humans, if you feed a human too much it will vomit so…don't do that. A light meter helps you set your light levels and it's up to the grower to adjust it from there. Or a grower can set it to whatever level they want and see how things go. For me, I'd rather set understand the conditions in which a plant will grow well and then create that environment for the plant. Other growers take a completely different approach and get good results, too.

Is this the best method? If I'm strict with the DLI recommendations on the site I'm looking at I may never crank the light up all the way which seems strange and pointless.. if back in The day a 600w hps was better than a 400w, then why not use the light to it's full potential?


What are peoples views on this please

That's completely up to the grower. In my experience (three years on this site and on two other sites), there's been a shift in how growers approach caring for their plants. Many growers avoid metrics, the preference being to continue the patterns that they've used over the years. They're getting good results and they're very happy with their processes. Some growers clearly exhibit antipathy to change, verging on the "we don't need to stinkin' badges" mindset.

More recently, in the past year or so, I've seen more grower who express interest in an understanding how to control the environment and who want to make the most of their equipment, and they're using products like the Pulse Grow or the AC Infinity products to set temperature and RH to keep VPD in line with recommended values.

More growers are using PAR meters and lux meters to measure light levels. I've also seen a change in how grow light manufacturers recommend that their products be used. Three years ago, running a light at 1000µmol "just wasn't talked about in polite company". Today, manufacturers sites and it's a very different story. Hang heights and dimmer settings are prominently displayed. They're publishing PPFD maps and talking about the spectrum of the light and the impact that the spectrum has on the plants. I've been in the technology business since the late 1980's so I've seen a tremendous amount of change. It is relentless.

A big issue is that technology is driving down the cost of the equipment so that it's now a commodity product. A light meter is $32 and, coupled with the PDF that I've written (attached), can be used to set light levels that are, arguably, as accurate as a $600 PAR meter.

I bought a PulseGrow for $200 three years ago. Pulse has a very similar product for $125, shipping now.

We have technology that allows us to create an optimal environment and it's available at a fraction of the cost compared to just a few years ago.

And there's more research available and it's more easy to access. In 2021, the main source of information that I could find was the videos by Dr Bruce Bugbee. He describes how plants respond to light, light color is referred to as "quality", and for many years he has stated that "light quality shapes plants, light quantity drives yield". Check out his vides on YT and that's one of the primary themes that he drives home. And it's there at the click of a button.

In the past few years, we've seen the Frontiers paper published and, just in the last few months, Mitch Westmoreland released the video with the Future Cannabis Project. That's new enough that it's "hot off the press" and it will take time for that message to be heard and acted upon.

In sum, there's no need to change growing processes to use these tools and techniques. After starting in early 2021, I had read through/watched most of the Bugbee videos and had read some of the research but it wasn't until, probably, my third grow that I decided to "do it". Why? I was swayed by conventional wisdom and "because…". It took a while for me to put the knowledge that I'd gleaned from those sources into action and I have no qualms about recommending that other growers follow suit.

This is one of the screenshots I took while watching the Westmoreland video. The video is about an hour long and light intensity is one of four topics.

 

[Delps8]

For reference,
The website I've been looking at is:
Photone - Grow Light Meter

And my set up now is:
4 x 4 tent
6" extraction
Circulating fan.
Heater (not needed atm)
Ac infinity humidifier
Phlizon FD6000 led light.

I use the Controller 69 ($125) + T3 Cloudforge ($50) + their heater ($100). With that gear, the only time VPD is out of range for any appreciable time is when I open the tent. My tent is in a 20' x 20' garage which moderates the temperature and RH. Coupled with that equipment, it's arguably an optimal grow environment for < $300.

Re. Photone - should be calibrated against a known good source. In my testing, Photone was 16% high (iPhone XS Max vs Apogee MQ-500).

One thing to keep in mind about using an iPhone is that the sensor in a mobile phone is designed to block "off axis" light (that's why the "diffuser" is required). Off axis light is a significant source of light in a grow tent and a light meter and a PAR meter are designed to capture off axis light. For my $$, I'd go with a light meter.

 

[Trump]

As was mentioned, I use these metrics as a guideline more than a roadmap. For example, optimal VPD is dependent on leaf temp also. Theoretically these are the best conditions averaged over a lot of different cultivars but....each cultivar is different in its likes and dislikes so, even though my VPD charts are telling me one thing I rely more on plant response rather than numbers on a chart. I've done runs where my VPD charts are telling me that my readings are in the danger zone but the leaves are happy as fuck. Guess which one I go by? I've done runs to the numbers on the charts and the yield was good. Not great but good.

Same with DLI. This last run I ran my DLI at CO² levels without CO². They loved it. What I like about DLI is it gives me a good base to start my observations in regard to plant performance limits. I'll start at the suggested and see how they like it. No reaction? Go higher. Leaves starting to taco? Pull it back a bit and let them grow into it.

I use a phone app for light meter that I compared to a dedicated light meter a friend of mine has and it was VERY close. Not sure if after some time the app will go off calibration but so far my grows have been pretty good so I'm guessing the meter is still close to accurate. The next time I see my friend I'll compare to see if it goes off calibration.

 

[Homebrew420]

Thanks for all the information and perspectives given in your replies guys, its very much appreciated.
It'll take me all night to address all the points and good information given .
I think where I am growing in a different environment to previous grows and all the information that is now available to me (for example, my old meter years ago was a stand alone temp/humidity meter, the cheap switchbot one i have now with Bluetooth also had vpd.. so i looked into it..) rightly or wrongly, I've been reading up on it, trying to follow it to a T.
I then came across new information that slightly differs from different sources and it threw my mind in doubt.. I now see they are guidelines to follow and assist with plant needs at given stages.
I'll look at some of those videos posted in the next days to get a broader vision of things.
Same as what you have delps8
Next on my list was to get the ac infinity controller 69 to control my T3 humidifier with vpd over humidity % . Also want to a get a dehumidifier connected as I find my vpd has been as low as 0.7 during lights off and feel this would be too low for when they are in flower with lights off
At the moment I've been trying to turn off the humidifier early before lights out to help with this, but that's not always going to be possible and like today, forget to turn it back on at lights on.

 

[Delps8]

Thanks for all the information and perspectives given in your replies guys, its very much appreciated.
It'll take me all night to address all the points and good information given .
I think where I am growing in a different environment to previous grows and all the information that is now available to me (for example, my old meter years ago was a stand alone temp/humidity meter, the cheap switchbot one i have now with Bluetooth also had vpd.. so i looked into it..) rightly or wrongly, I've been reading up on it, trying to follow it to a T.

Leaf surface temperaure must be included in the calculation of VPD for it to be accurate. I have Govee sensors in the canopy of my current plant and the Govee app reports VPD. Given that there's nowhere (that I can find) to assign a value for the LST, usually in terms of the offset from ambient, I disregard the VPD values from those sensors.

Re. meters - not to belabor the point but, they're all wrong. Key points are how wrong and does the meter wander over time.

Calibrating a hygrometer - there's the "salt test" and Boveda sells a "calibration kit" which is just a Boveda that holds RH at 75%. I've used both, the Boveda is easier to set up but both take at least 24 hours to conclude. I used Boveda to calibrate the "5 pack" of Govee's that I put in my plant and it took about 36 hours for RH to stabilize at 75%. Time well spent. And what was really impressive is that I put one of the Govee's next to the AC Infinity sensor for a day or two and the values matched.

I then came across new information that slightly differs from different sources and it threw my mind in doubt.. I now see they are guidelines to follow and assist with plant needs at given stages.
I'll look at some of those videos posted in the next days to get a broader vision of things.
Same as what you have delps8

Yeh, it's a learning process but it also took me some time to take what I'd read and put it into action. The info from the pointy headed guys was so very different from everything that I'd read on cannabis related sites that I was hesitant to make the change. Absolutely zero regrets for changing how I grow.

The Frontiers paper was an eye opener but after Westmoreland confirmed the Frontiers paper, I('m even more of an advocate. What still floors me, though, is how they're getting 2kµmol±. That's just wild.

Videos - Westmoreland deals with PPFD and its impact but the various Bugbee videos cover the entire grow environment. If you find the "DeBacco University" videos, when it comes to grow lighting, I think it's fair to say that he repackages the info that Bugbee has put out, though he does touch on other topics, as well. The only caveat for DeBacco is that he reads every slide and adds very little in his discussion so I found myself skipping from one slide to the next.

The Future Cannabis Project covers a wide variety of topics. They're well written and produced.

Next on my list was to get the ac infinity controller 69 to control my T3 humidifier with vpd over humidity % . Also want to a get a dehumidifier connected as I find my vpd has been as low as 0.7 during lights off and feel this would be too low for when they are in flower with lights off

Agree. When lights are on, plants photosynthesize, transpire, and respire. When lights are off, they transpire and respire. Pulse advises to try to keep VPD within 0.3units, IIRC. With the Cloudforge and the heater, I don't change it for lights out. At lights out, I let the temp drop to 76 (from 80-82 or so) but I leave VPD the same and let the C69 toggle Hugh on and off.

The graphic below is from the past few days. The line at the bottom shows the duration and intensity when Hugh runs. That display is controlled by clicking on the dropdown menu that opens when you click on the varying length horizontal bars to the right of the zoom dropdown. The dropdown menu shows the ports by port number and I usually just display Hugh and, sometimes, the heater.

At the moment I've been trying to turn off the humidifier early before lights out to help with this, but that's not always going to be possible and like today, forget to turn it back on at lights on.

I used mechanical timers in 2017 but, by 2021, digital tech had improved to the point where it couldn't make the case to not go in that direction.

I use Kasa Smart Strips for ($60±) for some of the equipment. My grow uses two 5 port smart strips but only a few of the ports are in use. The rationale for the five port model vs the three port (I think it's three) is the five port strip has energy info so I can see what's using the most electricity and it also allows me to do a quick and dirty tweak to my grow light. From time to time, I'll do a light reading and the values are "too high" (for me!) so I'll drop the wattage by, say 5%, to get PPFD into a range that I'm more comfortable with. Yeh, it's not that the plant doesn't like it — it's the "plant daddy" mindset that kicks in.

When possible, I use the Controller 69 rather than the Kasa because it has a level of programmability.

Funny - the external driver for my light is still set to shut off…now fixed.

My growlight doesn't work with the C69 because it pre-dates the C69. If I was buying a grow light now, it would be remotely controllable, no question.

You might want to grab a "Pohl Schmitt Electric Dehumidifiers", as it's labeled on Amazon. It run $40 and it drops the RH in my grow by about 7%. Per my grow journal, my current grow is…anemic, to be kind, but I ran a Vivosun in the tent and it did nothing so I was pleased when I could see the impact of the Polder (one reason why I put the Govee's in the plant).

 

[Homebrew420]

Sorry delps8, I read through all of this after you posted and didn't reply, I've even researched the dehumidifier and plugs.. never knew the WiFi multi plugs were a thing! They will come in very handy!
Controller 69 makes a lot of sense and helps from flying blind so to speak when your away, I do have a camera set up so I can see what my temps/humidity are on my switchbot meter I have in there and also have a temp controlled WiFi plug that I can intervene with.. be it very limited.

 

[Delps8]

Sorry delps8, I read through all of this after you posted and didn't reply, I've even researched the dehumidifier and plugs.. never knew the WiFi multi plugs were a thing! They will come in very handy!
Controller 69 makes a lot of sense and helps from flying blind so to speak when your away, I do have a camera set up so I can see what my temps/humidity are on my switchbot meter I have in there and also have a temp controlled WiFi plug that I can intervene with.. be it very limited.

"Sorry delps8, I read through all of this after you posted and didn't reply," - I appreciate the sentiment but no apologies needed. I'm glad you found the info helpful!

Re. the Kasa smart strips - they're still on sale at $44 for the six outlet model. That's steal.

If you've got camera viewing sensors, that's a big step in the right direction. I started with a PulseGrow and an Inboard RH controller and, as temperature changed over the course of a day, I would bump the RH up or down. That was a huge time sink and I gladly retired both of them for the C69. I got an incredible yield for that one grow but I believe it was by luck — the big issue was that I embraced the research and switched away from "600µmol is all you need" in flower.

It's good to keep VPD in range but it's a secondary issue. The big issue with VPD being out of whack is that VPD drives transpiration and, if it's too high, the plant can't use all of the chemicals and nute burn ensues. VPD has to be quite high to do that but I've seen more than one grow journal where that happens. In contrast, if VPD is even in the ballpark, yield will be a function of light. More light, as long as your plants can tolerate it, allows plants to generate more glucose and that allows them to grow larger, more healthy plant. VPD, nutes, etc, are the supporting cast - light is the main driver.