The spectrum is not a different topic, you can put 1800 PPFD of a green spectrum and that study would not tell me anything, the same as that study that uses purple LEDs with blue/red and without using the other bands of the spectrum, especially green/yellow and infrared that affect the leaves more.
When I wrote the discussion about what is "good" is a different discussion I meant that good is a separate discussion. Unless the term "good" is defined, then it's undefined and, at best, meaningless.
"you can put 1800 PPFD of a green spectrum and that study would not tell me anything" - that's your decision about the paper, not a comment on the inherent value of the study. A research document is designed to stand on its own. Here's what we wanted to find out, here's what we did, here's what we found out.
If a study uses green light and get results X, Y, and Z then that tells us that a study used green light and got X, Y, and Z. It really is that simple. Issues can arise when readers try to extrapolate from the study but that's not a problem with the study.
It's completely valid to criticize a study but it requires clear and mutually understood terms and the onus is on the researcher to openly and honestly report their findings.
If you don't like how something was done in a study or disagree with the methodology, you might contact the authors of the study and provide them with your questions and observations. That's how scientific progress is made.
