How do you grow and get shorter internodal space I’ve had this issue.
Some of it is strain dependent but the spectrum of your grow light and the amount of light have a very large influence.
Historically, growers used metal halide lights in veg and high pressure sodium in flower. The spectrum for MH had a lot of blue photons and blue photons inhibit cell expansion in plants so plants grown under a light with a lot of blue will be short and stocky. HPS, with a lot of red, allows plants to grow taller so the MH + HPS combination worked out pretty well.
Along comes LED's and white LED's have pretty much taken over the market with a balanced spectrum that has a good % of blue and a good % of red.
The other piece of the equation is to give plants lots of light. Light is the only way that plant can generate food. If there's not a lot of light, they will stretch to get to the light. We see when seedlings don't get much light - they're tall and slender and, if the situation isn't fixed, they have a hard time supporting their own weight.
Lights for a small space (2' x 2') tend to have more blue in the spectrum than lights for larger spaces. I suspect that's because with more blue in the spectrum, which tends to keep plants short, it helps stop the plant from growing out of the 2' x 2' tent and manufacturers don't want that to happen. Once you get to a 2' x 4' or larger, many lights have a higher % of red.
Most (almost all) LED lights on the market today are white lights. Until last year, Growcraft made separate veg and flower lights (I've used their lights) and, today, HLG sells "B spec" and "R spec" lights. Growcraft switched to white LED's last year but I think they're no longer in business.
Separate lights can be a lot of work and, while the results can be really amazing, most growers (understandably) can't be bothered to get that involved. What's way easier is to get a light that has a very high PPFD and then give your plant as much light as it can tolerate. That's referred to as "the light saturation point". In addition to getting a good light, it's money well spent to buy a light meter. I have a Uni-T ($32) and it's, in practical terms, as accurate as a $600 Apogee PAR meter.
An important distinctions is that key point is that the meter tells you how much light is falling on the plant but the plant tells you how much light the plant can use.
Putting too much light on a plant will result in a plant telling you you're giving it too much light (duh!). It will indicate that by having the leaves "canoe" or by rotating the leaves vertically, like a Venetian blind, among other reactions. You
can damage your plants. For example, if you crank up the light and leave the grow for a few days, you may well damage your plant. That's negligent and you will lean, hopefully, not to do it again.
I've had two instances of things going sideways where my plant got >1200µmol. One issue was because I switched on the wrong switch on my Pars SP 3000 and didn't check the light levels. About 30 minutes later, I saw that the temperature in the tent was really high. When I got to the tent, I figured out that the switch that I hit was the "all on switch" that bypassed the dimmer.
Some of the leaves had tacoed or turned away from th light and, after about half an hour, they hard gone back to their normal orientation.
The other time was when the $10 dimmer on my $600 Growcraft went on the fritz and the light went to max power. I contacted tech support and shared my thoughts on that design decision. The result was similar - everything, well almost everything back to normal. What didn't get back to normal was that one cola was bent at the top. That looked pretty strange but there was no physical damage.
What do you get from turning up the light levels?
A happy plant - "They look so happy, they should get a room".
Check out some grow journals and you'll see that some plants are rising up to the light - that's called "praying". My belief is that, when they're doing that, they're right on the cusp of too much light but I'll admit I've never tested that. I
think it's a good sign to get plants to the point where they're praying.
You also get a plant that's easy to harvest because there are a lot of branches that are close together (vertically) and the flowers are also close together so they merge into what I refer to as "a donkey dick" cola. I've had some colas from my autos that are as long as my forearm.
The quantity of the harvest increases in an almost linear manner with the increase in light levels. Roughly speaking, yield increases at 4-5% for every 50µmol increase in PPFD (see attached "Frontiers" paper).
I've recreated this table from the Frontiers paper:
And the quality is high, in terms of lots of flower and not many branches. I refer to them as "a shrubbery" a la Monty Python.
The plant below is probably the best shaped plant I've grown. It was grown with veg and flower lights, as well as topped and LST'd. Harvest was a breeze because the plant was only 2' tall.
Wow, long response (I'm laid up with my first bout of Covid) — what was the question?
Hope that's helpful.
