Heres a Very Interesting Study On Photoperiod

MDPI
https://www.mdpi.com/2223-7747/13/3/433
Longer Photoperiod Substantially Increases Indoor-Grown …
Web6 days ago · Ahrens, A.; Llewellyn, D.; Zheng, Y. Longer Photoperiod Substantially Increases Indoor-Grown Cannabis’ Yield and Quality: A Study of Two High-THC Cultivars Grown …

I've seen some threads where people run 14/10 and say it increases yield. It makes sense. I've also seen a thread that says shorter photoperiod produced better quality, but that might just be because they're comparing fully done buds to almost done buds. Not sure but this is one of the threads talking about the 10/14 schedule. I have a couple plants at 9 weeks now that still have a long ways to go so I've been dropping the hours of light to try and speed them up. The buds are already big enough and the longer they take the more chance that I mess them up so I dropped to 11/13 for a couple weeks and last night set them to 10/14. I've always ran 12/12 so this is new to me but it looked like they started developing faster when I switched to 11/13.

Many thanks for posting this!

More light = more yield?

The longer photoperiod got a higher DLI. Also worth noting is that they used a PPFD of only 540 umol/m2s.

Lou66 said:

More light = more yield?

The longer photoperiod got a higher DLI. Also worth noting is that they used a PPFD of only 540 umol/m2s.

Click to expand...

Move light = more DLI, no doubt but that's not the issue they were after (interestingly Zheng, a former Bugbee student, collaborated on the attached paper).

To my little history-major-brain, the fact that they didn't control for the increased DLI is a problem. I'm surprised to see what they did. Put aside the meager light level but by changing both the photoperiod and the DLI, I'm not clear on how they can draw conclusions. It looks like a fatal error but I haven't read the paper, start to finish.

Having said that, something's happening here and what it is isn't exactly clear. The DLI change was tiny yet the changes that they recorded in outcome were very significant. If you plough through the attached paper, they're reporting that a 50µmol increase in PPFD about a 5% in crop yield.

This table is based on the information in the Frontiers paper:



The change in DLI is only 1/12 ≈ 8% yet they're seeing significant changes in lotsa other goodies. When you read the Frontiers paper, IIRC, they found no increase in "potency" - just more weed and higher "quality", meaning the ratio of inflorescence to above ground plant mass.

Funny how two similar expirements can appear to come up with different results.

Great to see actual research re. light. I'm a Bugbee acolyte and a believer in "turn it up to 11" when it comes to light levels. Light levels from my current grow, one Glookie in a 2' x 4' tent, day 37.



LR = left rear, RF = right front, etc. Flower light is a Growcraft X3 at 283 watts running 24/0
Column 3 is DLI. 72 is standard deviation of PPFD; 6 is SD of DLI.

I’ve been using Joe Pietri’s flower lighting schedule and I’ll never go back.
7 on
17 off
Plants finish faster and are just as big if not bigger than when using 12/12. Plus saving money on electricity.

Just did my first pass through this paper and they do address the DLI ∆ vs the ∆ in photoperiod.

From their discussion:
"Given that the increases in inflorescence yield were disproportionately higher than the increase in DLI, flowering photoperiod management may be one of the most efficacious cultural practices available to commercial indoor cannabis cultivators for increasing yield that is both simple and cost-effective to utilize. "

As usual, the devil is in the details but extending the photoperiod might be worth a shot. I've got a plant in day 4 of flower and, as much as I'd like an X% increase in yield, my concern is that the plant might reveg. I had two failed grows last year (ouch!) so I'm not in a position to use this grow as a guinea pig. Based on this first read through, it might be worth a try for my Fall grow.

One valuable nugget will answer the eternal question - "How do I make my buds more dense?" - this may well end up on my headstone, "give your grow more light!"

"Apical inflorescence density has been shown to increase linearly with light intensity (Rodriguez- Morrison et al., 2021)"

I've attached a (marked up) copy.