Hi!
So in my spare time I’ve been reading about LED’s, PAR, PPF, and PPFD trying to grasp everything and how to apply it when making a light choice. I thought I would share some of what I have found that has really helped me in determining what to choose, what blew away a common misconception for me, and how to call BS on LED makers.
I’ve been reading about PAR and PPF from books, but it never actually clicked in my head until after I read this article from fluence:
This article below explained to me how Cannabis utilizes PPFD along with Co2 (included is a tl;dr)
And for those of you who enjoy a tl;dr:
umol/s = Micromoles per second. For reference, at noon in California during the summer, the sun can give off 2,000umol/s!
PPF: This is the umol/s, or better described as the emission of light from the source. All bulbs give this off and should be included when choosing your light! An example:
Gavita Pro HPS 1000W (With Philips Bulb) has a PPF of 1.72/W (It gives off 1,720 umol/s at the light’s source). This rating clearly beats out quite a few LED’s, but you’re also spending the money for electric, a balast, replacement lights, and it puts off quite a lot of heat. While compared to a quality LED light you can have over 50,000 hours of light (5+ years), you use less electric, and you don’t have the issue with heat!
PPFD: It is the measurement of PPF (micromoles per second) at a specific height, such as 6" from the canopy of a plant. ** Please look at quote below for more regarding this.
Update: The number of umol photons divided by the area multiplied by the seconds will give you ppfd.
umol photons / m2(s) is the formula. Watch this video here for another explanation:
I have searched and searched but I have not been able to locate a solid formula or a way to mathmatically calculate the PPFD area just by using a light’s PPF with the addition of adding height to the equation. As far as I can tell, the best way to acquire these measurements accurately is to acquire a LUX (requires a conversion table found here: PPFD to Lux Conversion) or PAR meter and take measurements at different parts of you canopy to accurately calculate how much PPFD your plant is receiving.
How Co2 Plays into this: The more Co2 that is in the air (PPM) above natural Co2 levels (Roughly 400ppm) will allow for more light to be used in photosynthesis (PPFD)
DLI: This stands for Daily Light Intergral which is a measurement that shows the intensity of light delivered, over a square meter per day. To convert PPFD to DLI, do this:
PPFD Given Value: 100umol/s (We’ll start with this to make things easy)
Take your 100umol/s and multiply by 60 to get umol/minute (6,000umol/minute)
Multiply 6,000umol/minute by 60 again to get umol/hour (360,000umol/hour).
Now, this value is getting large, so now we have to convert from umol to mol (Micromoles to moles)
We take our value of 360,000 umol/hour and divide it by 1,000,000 to give us .36mol/hour.
We take that value and multiply it by however long we let our lights run (let’s say 18 hours)
.36mol/hour * 18 = a DLI of 6.48
So for cannabis, bottom threshold for optimal growth and photosynthesis is a DLI of 22 would be:
24/0 schedule: 254.6 micromoles/m2/s-1 (That’s everything done above, but the mol/hour is multiplied by 24 to give a DLI of 22)
18/6 schedule: 339.5 micromoles/m2/s-1
12/12 schedule: 509.25 micromoles/m2/s-1
For Cannabis, the Top threshold for optimal growth and photosynthesis is a DLI of 65 moles per day.
*** extremely important notice, only go up to these amounts if you are using supplemental CO2, do not go this high if you are not using supplemental CO2 as you will actually slow down photosynthesis and waste energy.
24/0 schedule: 752.31 micromoles/m2/s-1
18/6 schedule: 1003.08 micromoles/m2/s-1
12/12 schedule: 1504.6 micromoles/m2/s-1
The generally accepted guidelines for artificial light PPFD in flowering are this:
in a 12/12
PPFD of at least 510 micromoles/m2/s-1 for the low end of optimal intensity
PPFD of at least 800-1100 micromoles/m2/s-1 for perfect optimal lighting without additional CO2.
PPFD of at least 800-1500 micromoles/m2/s-1 for perfect optimal lighting WITH additional CO2.
-What I’ve found is that a good LED manufacturing company will publish this information and has made choosing what lighting I would need for my grow a breeze. It also taught me that the Wattage rating for LED’s is not what matters (The whole Watts/sq.ft thing) but you should look more for a good PPFD rating at whatever height you plan on hanging your lights at.
-When figuring out what light I want, I now have the knowledge to go through and look at these values and pick out what light is going to suit my needs based off of whether or not I’m going to use Co2.
**A note to readers: I’m not the best at presenting things in an easy to read manner, as a result this post is a work in progress as I try to improve it to deliver the best content possible. If you have any suggestions, please feel free to post them!
Credit:
I have to give credit where it is due, if I hadn’t asked @dbrn32 about some LED recommendations, I would not have found this information so easily and figured out how to piece everything together.
More on PPFD, courtesy of @dbrn32
*Actual Real World Application:
When it’s released, I plan on purchasing a SPYDR 2p LED from Fluence and below are the Manufacturers Specs.
PPF: 1580umol/s
Input Power: 632W
PPFD@6" (over a square meter): 987umol/s
PPFD@12"(over a square meter): 949umol/s
How is this going to meet my requirements? Well:
On an 18/6 Schedule, at a PPFD@12" would give me a DLI of 61.5 mol/d
This is going to require Co2 Supplementation to increase the rate of photosynthesis (otherwise that extra light is going to waste) unless we have a controller that can dim the strength of the light to lower the DLI to a level that doesn’t require Co2.
For my 12/12 schedule I would receive a DLI of of 41 at 12" but if I lowered the light to 6" it would be 42.6. Not a whole lot of difference, but it’s still more light that I can use some Co2 with if I so desired, as shown above 800-1100 umol/m2/s is still able to be done without Co2 but you can also add Co2 if you like, which I plan on doing (800-1500).
So now, if I purchase this light, to use it at full strength, I know I will have to have Co2 supplementation to my grow room in order for it to be worth it.
(Specs on the SPYDR2 series can be found here: https://2xuwao2gok1v2wn2em9n5ys8-wpengine.netdna-ssl.com/wp-content/uploads/2018/08/SPYDR-Comparision-Web-Spec.pdf)
Question to readers over a mistake I probably made: Regarding Co2 use and DLI, I know the low and high ends are correct, however Im not 100% certain at what DLI you HAVE to start using Co2 and at what minimum DLI Co2 is actually beneficial at.
