From the perspective of the plant, there's no need to do that.
Growers are, overall, scared that they'll hurt their plants by giving them too much light and, as a result, don't get the most from the plants. It's almost impossible to harm a cannabis plant when using an LED. I have seen it done, once here on RIU.
Having said that, I routinely give my plants a little too much light in mid-veg—after bumping up 100µmol over night, a couple of leaves started to curl up so I turned the dimmer down to its previous setting. After about an hour, the leaf uncurled and that was that. I waited until the next day and bumped the PPFD.
This is the entry from my grow journal. That was day 29 and I had to back down from 798 to 750.
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If you're at 50% at 18", you're putting only 650µmol on the plant at the center of the tent and that drops off quickly. AC Infinity is using a 9" grid for their PPFD maps vs the 6" grid used by most other companies. This overstates the values. I would argue that there's only an average of 500µmol of light in rectangle formed by those four grid squares in the center.
View attachment 5479464
Figuring out the number is "all fun and games" but, insofar as the plant is concerned, it does not matter. If you want to increase the yield of your crop, give your plants more light. Light is the only way plants can make food and your plants are
nowhere near the light levels they need to reach their genetic potential.
How much light can your plants use?
They will tell you, the same way that my plants told me—if you give them too much light, the edges of some of the leaves might curl so you just turn the dimmer back down. Seeing that your plants is well established, you should be able to give it a lot more light than you're giving it now.
There is no need to increase light levels. Cannabis will grow, in ambient CO2, at light levels between ~70µmol and ~1000µmol. The only question is how big a crop you want from your plants.
