Well, I've had this debate before but we can do it again.
I know what PAR is and what it measures but the question is: do the measurements matter in the real world? The answer is: no, it doesn't.
The problem with PAR is that it only measures specific spectral wavelengths between 400-700nm. That would be fine if everything fit in that range but most grow lights put out more than just 400-700nm and plants actually use more than 400-700nm despite a lot of sales propaganda and outdated science.
If PAR really mattered then it would be easy to say that a 650w (actual draw) LED light that has the same PAR rating will yield and perform the same as a 1000w HPS light, right? In fact, that's what a lot of LED manufactures claim, based on PAR. The problem is that real world results show that it's not true. A 650w (actual draw) LED light is actually closer to 600w HPS in results and even that depends on grow styles.
Why is that? It's because, in part, LED lights lack the penetration power that large HID lights have despite having a higher PAR rating. It's also because plants use spectra that many LED grow lights don't provide and that aren't measured by PAR readings.
Even among (maybe even especially among) LED lights PAR is useless because different LED lights use different spectra, some out of the 400-700nm that PAR uses. Some LED lights are only red and blue some go as high as 16 wavelengths including IR and UV which are not measured by PAR.
This is why high powered HID lights beat LED lights that have as much or more PAR than they do every time. That is why PAR is little more than a sales tool used by LED manufactures and retailers to try to justify the high cost of the lights and compete with proven HID systems that cost less and perform better.
Show me the low powered LED light that can out perform a 1000w HPS and I'll change my mind but such a light does not exist...so far. We have a lot of journals here and none back up the LED manufacturers claims that are based on PAR.
Hope that helps...