i know i am coming too late to the discussion but hoping it will help others in the future. the thing you need to know about par and ppfd is that your plants need different amounts at different stages of growth. also, your environment will greatly affect how much light your plants can use. are you running co2? if so, your plants should be able to use a hell of a lot more light. in any case use the following table to determine how much light a plant should receive;
clones – no direct light and no more than 100 ppfd
early veg – 200 – 400 ppfd
late veg – 400 – 600 ppfd
flower – 600 – 900 ppfd (no co2) 1400 ppfd (with co2)
in order to determine ppfd at the canopy level you need a par meter. the good ones are ridiculously expensive. this is the one i use; https://www.amazon.com/Apogee-Instruments-Full-Spectrum-Quantum-Telescopic/dp/B09MYDTW5C/ref=sr_1_3?keywords=apogee+ppfd+meter&qid=1663021274&sprefix=ppfd+meter+a%2Caps%2C87&sr=8-3
