Be careful with DLI/PPFD, and grab a coffee.
Don't follow a dli charts blindly, or you may end up with issues. Here is what I mean by that.
Every plant has the ability to use more or less light than all the other plants. Light must be combined with other nutrients and catalysts inside the plant to be used (photosynthesized).
If the roots aren't capable of supplying enough nutes/water to match the amount of light going in, you get a deficiency. The plant will try to convert light to sugar faster than the supply chain can deliver the parts.
This causes great stress to a plant and likely a mag def will start to show. Mag usually goes 1st in soil.
So you must set your maximum dli to cater to your weakest plant, not the strongest. The chart doesn't tell you that part, it assumes your plant health is optimal.
If the plant can't photosynthsize fast enough to use all the light, it results in light absorbed but not used. Unused light raises plant temps and heat stress occurs.
Incorrect plant temps also causes transpiration issues and that compounds the entire problem, making things worse not better.
Any stress caused by light is a sure fire recipe for hermaphrodism. The short version... Too much light = hermies.
So watch your plants. 2 identical clones from the same mother in equal pots can require different ppfd/dli's simply because one may have the root system to move more water.
So when it comes to light you need to watch your VPD. If you dial VPD in properly, your DLI will automatically be set correctly. If your VPD is wrong, then you won't be driving your plant at the correct speed for the amount of light being given.
You need to ensure that both the roots and environment are capable of handling the amount of light being thrown at the plant.
The environment is what controls uptake, and uptake needs to match dli/ppfd. It's a circle and every time you do a lap you can raise the ppfd a little.
So you set your environment, which grows more roots, which allows a higher ppfd, which allows a raise in VPD, which grows the roots bigger, which allows a higher PPFD, which allows you to raise VPD.... rinse and repeat. The weekly chart increases assume you are doing this. If you aren't then there is a good chance your plant isn't optimal, so the chart becomes useless, and possibly a hazard.
It needs to be done in small increments, not all at once. The DLI charts are just general ballpark ranges.
VPD regulates stomata, stomata regulates transpiration, transpiration must match light intensity, and roots must be able to keep up to transpiration.
This is the reason a seedling can't handle 1000ppfd. It simply doesn't have the roots to supply that rate of photosynthesis.
Even if your soil is spot on, you will see a deficiency if the plant can't move the nutes in quick enough.
But free seeds are cool too. At least they will be feminized.
So I'm not trying to scare anyone, just understand what needs to be done before increasing light intensity, the plant needs to be prepped for it ahead of time.
A plant with excellent roots and a half-assed dli will give you a better harvest than a plant with half-assed roots that matches the dli chart perfectly.
