Trying to definitely understand how to best measure light, specifically in an LED context. Two questions:

1) I've seen equally strong preferences for measuring light in lux, using free apps, or in ppfd, using math I don't understand. Is lux approximate while ppfd is much more accurate, or do they measure different things? I get confused when ppfd measurements bring in a time factor (e.g. not just how much light is hitting a plant, but how much is hitting a plant per second/day/whatever and why it matters).

2) With LEDs (full spectrum, not blurple, thinking of Spider Farmer lights specifically), I understand they have a lower light "intensity" (might be the wrong word, but run with me here) than other light types, meaning the "higher quality" light with stronger canopy penetration is much closer to the diodes. How do you measure that with dimmable LED setups?

Trying the gauge if there's a difference between LEDs very close to a plant on a lower setting (dimmed to 20-30%) vs. further away at the highest setting (100%), and if there's a way to calculate the sweet spot--or if it even matters, because the manufacturer recommendations already did the hard work of figuring that out.

Manufacturer specs for the SF-1000 attached for reference. So much of the discussion around this predates full spectrum LEDs, it's tough to translate.

Worth noting the official product page includes lumens, which for the SF-1000 is 16439Lm±5%@AC120V (AC120V is a standard US 110v wall outlet).