Aqueminianswered grow question 3 years ago It's not exact, it's all about preference. But here's some good information to go by but even this is outdated I believe. I don't think this accounts for Co2 grows that can use MUCH more light.
Recommended PPFD levels for the establishment phase of cannabis are 75-150 µmol/m²/s for cuttings, and 100-300 µmol/m²/s for seedlings. For cannabis in the vegetative stage, PPFD levels of 300-600 µmol/m²/s are recommended and may be increased to over 600 µmol/m²/s in the reproductive phase.