I was surprised by how low his recommendations are for DLI values. In the same way that the folks at growlightmeter.com have zero research for their recommendations, I haven't seen or heard of any research that Shane uses to support his recommendations. However, he has geared his products to support those light levels so I'll give him marks for consistency.
The light saturation point for cannabis is 800 to 1000 µmols and cannabis can be grown under 24 hours of light. My past three grows were autos and I ran them using 18/6. As far as the plant is concerned, there's no need for that. My current grow, germinated 9/1/22, was going to be 24/0 but I checked my electricity bill and discovered that my rate per KwH was 61¢ between 1700 and 2000 versus 34¢, so I went to a 20 hour day with the lights off between 1730 and 2030. That'll save me $250± per grow so I made the change. Were the cost of electricity level, I'd run 24/0.
Re light cycles - there's nothing that cannabis does during lights out that it doesn't do with the lights on. The "dark cycle" is a complete misnomer, the real name being the Calvin cycle.
Re. DLI's - Bugbee's most popular video and the paper by Chandra illustrate that the curve for net photosynthesis (Pn) starts to roll off when PPFD > 500µmols. I assumed that Pn was a proxy for yield and accepted that, even though it's not a linear relationship, the electricity bill would be higher but at least I'd be getting more weed. That turned out to be close but not quite on target.
The key point is that we're not harvesting photosynthesis, we're harvesting (well
I'm harvesting) cannabis flower and the good news is that, while Pn is not linear, it turns out that plant yield, crop yield, and crop quality are linear meaning that the more light you give cannabis, you get more growth from the plant and the ratio of flower to inflorescence increases. Refer to the Bugbee video about indoor hemp production - it's extremely informative about the relationship between DLI and yield, as well as a host of other issue. There's other research that confirms Bugbee - I can find the cites if you're interested.
I'm a believer in "big light" but I ran "regular" levels for a couple of grows and, sure enough, everything turned out fine. About halfway through the third grow, after watching a DeBacco video for the Nth time, I decided to "turn it up to 11". Check the grow journals at the links and you'll see how things turned out. My light levels for my current grow are below. The DLI's are for the average values from the two plants. The only time I've seen any evidence of too much light is when some of the PPFD values were well into the 950 - 1050 µmols range. At 850 to about 950, this strain is doing quite well.
Again, running autos at a DLI of 40 moles or gradually ramping up light levels will get a very acceptable crop but there's no particular reason to limit your yield by sticking to those light levels. Per Bugbee, a lot of his clients are leaving a lot of money on the table by not giving their plants high light" and, as long as the rest of the grow is squared away, cannabis will click right along at DLI's > 60 mols.
and a family portrait:
) as with the regular led board when close to the crop the flower under the left side of the board doesn't really benefit from the light coming from the right side, a bit more at height but it still very much a top down situation.. if one were to hang two HPS lights next to each other you'd see a lot of shadows disappear or shrink.
