Hey mate still got the light at 400 just now, but 3 of the plants are looking a bit droopy, feeding 500mls a day at 1.3EC but that’s giving me more than 20% runoff going to back it down slightly so getting a bit less.
First photo is 3 I’m talking about, 2nd is all of them other 5 looking better.
At 400µmol, your plants are getting about 50% of the light that they can use to achieve their genetic potential.
When I tested Korona/Photone back in 2021, the programmer didn't specify the weight of the paper that's used as a diffuser. I discussed that with him (email) and I think he went with #22 paper. After testing Photone, I found it to be 16% high and, as a result, recommend it only after other options have been explored.
If Photone is reading 16% high for you, your plant is getting about 350µmol. That's seedling/early veg levels. You can go as low as 64µmol for cannabis so it won't die at 350 but your crop will be modest.
Re. the chart from Photone. When I asked the programmer about the sources of information for the chart, he directed me to the footnotes on the page. There were none. I also asked him about recommendations of autos and he said that they considered autos to be "always in veg".
Since 2021, they have added a septette diagram for autos.
The only values that are close to being optimal for crop yield and quality are in some of the later weeks of flower. I say that because I grow my plants "according to research" and, in the later weeks of veg, my grows max out at the DLI's that GLM.com recommends. Other than that, their recommendations are not supported by what we know is the best approach to allowing a cannabis plant to thrive.
Cannabis
is a light whore loves light. I've seen no other site that recommends dropping DLI after going into flower. Other sites and most grow light manufacturers recommend increasing light levels and, overall, their recommendations are very conservative. By that I mean, if you follow their recommendations you will get a good crop. If you want an excellent crop, you should feed your plants as much light as they can handle.
A grower will lose more yield in their crops by not giving their plants light than they do by giving their plants too much light.
A fact - it's very hard to harm a cannabis plant by giving it too much light. I've had that happen a few times, some times because I push my plants and a couple of times due to equipment failures, but in all cases (except one) within a few minutes of my realizing that the light levels were too high, the plant had returned to its normal shape (the leaves uncurled). The one case where the plant didn't return to its normal shape was a cola that got bent about 2" from the top. Not a big deal.
The other side of the spectrum (sorry) is that growers don't know to or refuse to give their plants more light so they "leave money on the table".
This chart is from the cited source (copy attached)
Simply put, the change in yield between an average of 600µmol and 900µmol will be in the range of 5.2+4.9+4.7+4.5+4.3≈20%. Some growers would like to have an extra 20% yield but, I'll be the first to agree that cannabis will provide a good yield at moderate light levels. On the other hand, if you're willing to turn up the dimmer a bit, you'll end up with not only a larger crop but, if you give your plants a lot of light from the jump, you'll get plants that are much easier to work with.
Roll back to seeing plants that are tall and slender, with not a lot of leaves and lots of internodal space. Those are classic symptoms of plants that aren't being fed well. On the other hand, a cannabis plant that gets a lot of light will be more "full" - lots of branches and leaves with short internodal space. That will, on one hand, tend to give you a more uniform quality between the top and bottom buds but the shorter plant is much easier to work with than a tall, gangly plant.
I strongly recommend that growers watch one or both of these videos:
Westmoreland is a PhD candidate under Bruce Bugbee and his research comports with and builds on existing research.
So, yeah, your plants will grow at 400µmol (but probably lower) but you'll have much better results if your plants are getting twice that amount of light (or more).