Lighting which to use to dial in DLI
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PPFD. There's a lot of calculators available on the web that can do it for you too.
PPFD
In my limited understanding, you would compare PPF to PPFD to find out how efficiently you were transmitting radiation from the light source to the intended target.
In my limited understanding, you would compare PPF to PPFD to find out how efficiently you were transmitting radiation from the light source to the intended target.
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Yep looks like I’m around 62 DLI…. Going to drop it to 75% power and raise it to 13/14” and I should be around 43 DLI!!! Thanks
Cannabis can thrive at 62mols - that's the DLI I use as my target DLI, in fact. The light saturation point for cannabis is 800-1000µmols. After that, CO2 becomes the limiting factor.
As DLI increases, there is a direct, almost linear increase in crop yield and crop quality. If you want more weed, give your plants more light. As Bugbee says, the rest of the grow has to be in order but, unless you're seeing signs of light stress, give the plants food. If light levels (assuming LED) are too high, the first sign usually is that the leaves on the canopy that are closest to the light will turn away from the light - "light avoidance". With gas discharge, the big issue is heat - that'll cook a plant. With LED, it's hard to cause tissue death in a plant.
Light and nutes are very different. The goal of fertilizer is to get chemicals to a plant so that those chemicals are in the "sufficiency" range in the plant. As long as you keep them in the sufficiency zone, the plant will do fine, and there are hard limits above which the plant will suffer, regardless of the rest of the grow environment.
With light, as Bugbee mentions in a couple of his videos, researchers have hit cannabis with > 2000µmols and the photosynthesis and yield keep increasing.
Oh, yeh - PPF is the amount of photons being generated. PPFD is the amount of photons hitting a square meter per second. PPFD is the number you want.
You can do a rough calculation to determine mols - 1000µmols for an hour is 3.6 mols so at 800µmols for 18 hours is 54 + 10 = 64 and knock off 20% (12'ish) and you get low 50's for a DLI. That's rough math but it's close enough because the actual DLI does not matter. What matters is getting plants into high PPFD values and seeing how they react. A $500 Apogee can give you to a given PPFD reading with more accuracy but, once you've hit a certain light level, it's up to the grower to fine tune things.
I tested Korona (AKA Photone) on my 2017 blurple when I started growing again 2 years ago. Photone choked so I bought an Apogee. Since then, I've tested the Uni-T lux meter on a few different lights and, if I didn't have an Apogee, I'd buy a lux meter and do something with the $550 that's leftover.
Re. "should be 43" - the folks at growlightmeter.com push that a number but, as with Shane at Migro, they're giving numbers that are "conservative" and they have zero research to support their recommendations. I've emailed the programmer at growlightmeter.com (I've been writing software for a living for 30+ years) and he told me that they recommend 45 mols (or whatever) for autos "because they're always in flower", whatever that means. And 43 is the DLI that you get when a photoperiod plant is in flower (12 hours of light) at 1000µmols. There's nothing in cannabis research that talks about numbers that low. In fact, Bugbee talks about "high light" where "high light" levels start at 43 mols.
Having said that, cannabis will return a good crop at 43mols. The light compensation point, below which plants cannot produce enough glucose to sustain life, is 64µmols for cannabis so growers could drop their lights to low seedling levels — think of all the money they'd save on electricity! ;-)
As DLI increases, there is a direct, almost linear increase in crop yield and crop quality. If you want more weed, give your plants more light. As Bugbee says, the rest of the grow has to be in order but, unless you're seeing signs of light stress, give the plants food. If light levels (assuming LED) are too high, the first sign usually is that the leaves on the canopy that are closest to the light will turn away from the light - "light avoidance". With gas discharge, the big issue is heat - that'll cook a plant. With LED, it's hard to cause tissue death in a plant.
Light and nutes are very different. The goal of fertilizer is to get chemicals to a plant so that those chemicals are in the "sufficiency" range in the plant. As long as you keep them in the sufficiency zone, the plant will do fine, and there are hard limits above which the plant will suffer, regardless of the rest of the grow environment.
With light, as Bugbee mentions in a couple of his videos, researchers have hit cannabis with > 2000µmols and the photosynthesis and yield keep increasing.
Oh, yeh - PPF is the amount of photons being generated. PPFD is the amount of photons hitting a square meter per second. PPFD is the number you want.
You can do a rough calculation to determine mols - 1000µmols for an hour is 3.6 mols so at 800µmols for 18 hours is 54 + 10 = 64 and knock off 20% (12'ish) and you get low 50's for a DLI. That's rough math but it's close enough because the actual DLI does not matter. What matters is getting plants into high PPFD values and seeing how they react. A $500 Apogee can give you to a given PPFD reading with more accuracy but, once you've hit a certain light level, it's up to the grower to fine tune things.
I tested Korona (AKA Photone) on my 2017 blurple when I started growing again 2 years ago. Photone choked so I bought an Apogee. Since then, I've tested the Uni-T lux meter on a few different lights and, if I didn't have an Apogee, I'd buy a lux meter and do something with the $550 that's leftover.
Re. "should be 43" - the folks at growlightmeter.com push that a number but, as with Shane at Migro, they're giving numbers that are "conservative" and they have zero research to support their recommendations. I've emailed the programmer at growlightmeter.com (I've been writing software for a living for 30+ years) and he told me that they recommend 45 mols (or whatever) for autos "because they're always in flower", whatever that means. And 43 is the DLI that you get when a photoperiod plant is in flower (12 hours of light) at 1000µmols. There's nothing in cannabis research that talks about numbers that low. In fact, Bugbee talks about "high light" where "high light" levels start at 43 mols.
Having said that, cannabis will return a good crop at 43mols. The light compensation point, below which plants cannot produce enough glucose to sustain life, is 64µmols for cannabis so growers could drop their lights to low seedling levels — think of all the money they'd save on electricity! ;-)
Just use a dli calculator app from your app store or even off google, but ppfd is used in the calculations.
Also I dont know what kind of phone you have but theres pretty good apps to get accurate ppfd readings, photone works on both android and iphone, and I believe ppfd app is android only. But theyve both been thoroughly tested next to an apogee sensor and was within 1-5% on both apps. They also both have dli calculators built in so you can get that while you're taking readings too. Just gotta select the light style closest to yours and fill out the power and hang height. Can even do PAR mapping
