Lowering PPFD at the end of flowering – good idea?

I disagree any type of massive study is going to add anything that we don't already know objectively and categorically (other than possibly categorizing subtypes or trends amongst progeny). Lowering your PPFD at the end of flowering will decrease the available photons to the plant. This means two mechanism will be impacted. First, less photons means less energy to repair damaged trichomes and form new substances in those little factories. Second, less photons means less damage to trichome heads during the day. Extrapolate this out and there is no clear answer. What are you optimizing? Do your plants already look soaked with resin but you're just letting them ripen a little? Then yes, lower it to protect what is already there if you're happy with it. Are your plants still actively forming new trichomes? Likely not worth it to decrease it. I have found that photon density has nothing to do with end of life effects indoors, this is different outdoors when spectrum is literally everything (example: light leaks outdoors not mattering because of the sun and key properties...). Photoperiod length is what they meant. If you want to ripen quicker, shorten your days. Then your PPFD over time (DLI) is going to change...so then you increase your lights to keep the same DLI or keep the same PPFD which would lower your DLI. So, they are correct but only correct like accidently discussing the correct dew point because you happen to be at the right temperature. So, just ask yourself, what is your goal? Does the math support that goal? If someone can't clearly explain their statement on this topic I'd ignore them.

What do you want : mature, wenn developed buds with a complex Cannabinoid & Terpene Profile What Happens when decreasing DLI at the last weeks of living cycle? - lower DLI signaling like in nature the start of fall season & signaling the plant to come to an end ( produce the last bits of Terps/Cannabinoids & structure ) Go for it like @Hashy said

Maybe. This is one of those things you definitely need a control group to compare to and a large sample size.. then repeat the experiement with wide variety of genetics. The human eye and a few plants in your basement is not enough evidence to support a confident conclusion. This is how bro-science starts, even if once in a while an guess turns out to be true. An assumption is made and no evidence is ever used to support it. Example 1: They used to say you can use 'green' light during a photoperiod's dark cycle and it wouldn't cause stress/herms. This is totally false. IT turns out green wavelengths are actually more detrimental to such an effect than other ranges of wavelengths, lol... Totally opposite of what bro-science repeated for years. Example 2: Flushing a plant near harvest reduces minerals in the flower. Absolutely not true. The plant has no excretion system. Flower doesn't store excess, lol. There's no 'flushing minerals out of a plant." Simply doesn't have a biological process to perform this function. Not possible. Yet, it was repeated for decades and accepted as truth. Making up a hypothesis is integral to learning and advancing. Making up a hypothesis and assuming it is true is a total failure. Such things need to be tested in a systematic way as outlined by the scientific method. Assuming just makes people look like asses. Then, their ego makes them deny that they were wrong or made such a silly mistake, lol. Their long-held beliefs are more important than facts.

I reduce the power on my lights over the last few weeks. I work with DLI and if I'm at 40 I'll try and lower it to 35DLI then 30DLI before harvest. I find the plants prefer it that way over keeping at 40DLI right up to harvest.

Hi würde ich nicht machen. Hast du Vorteile davon ausser ein paar Cent Strom sparen? Nein denke ich nicht. Ich würde sogar sagen das die Pflanzen bis am Ende die Energie aus den Lampen in die Blüten stecken.

Yes, but it all depends how far along you are and how the plant is reacting. Toward the final 1–2 weeks, especially after peak swell, lowering PPFD a bit can reduce stress, save power, and help trichs finish without pushing more foxtails. I usually ease off a little in the final stretch, not full dim, just a notch. Some growers even drop light hours to 10/14 to mimic shorter days. Trust your plant though, if she’s still bulking, don’t back off too soon.

I do it. not always but i did this time around. Ill also drop the light schedule to 11/13 or 10/1

Good idea for what? If you have an answer for that, it's philosophy.