This info is relevant to every grow light. Blurples or white. The key is the mccree curve. Everything in the photosynthetically active spectrum is considered par. But a light that is emitting between 640-660 and 430-450, ie. blurples, are actually more efficient than the white leds which provides ample amounts of green, yellow, orange etc etc.
The efficiency i’m talking about comes into play only if the two lights we’re comparing is built the same. From same material and all so that there is no actual efficiency difference with the components.
There are some shitty blurples for 50 bucks which i’m almost sure is worse than cfls :D
For white leds, cbxs for example, there are conversion factors which lets you calculate ppfd values based on a lux reading. Now would a cheap lux meter be perfect? No! But its better than nothing.
With blurples you need a quantum meter to get the actual ppfd if the information is not provided by the company.
You can calculate the overall par output of the fixture if you know the efficiency of the components but can’t calculate ppfd from that. Well you already know this shit :)
But in either case 1500 micromoles are 1500 micromoles.