I’ve been thinking about getting a Apogee PPFD meter and have been doing some research. The video looks at measurements for the HLG 135W and 260W kits, which many of us have.
Based on a number of sources, saturation occurs at approximately 300 PPFD for seedlings / clones, 600 PPFD for veg, and 800 PPFD for flowering ladies. This is without supplemental CO2. With CO2 saturation I believe you could significantly increase effective PPFD levels.