Very technical question - LED wattage vs actual power used

So, it turns out that the small print is super important on LED wattage advertising. Long story short: my lights say they're 600w LED, my power meter say they're 100w. The 100w draw is indusputable, so my lights can't be 600w - right? Wrong. It turns out that the way LED's are marketed is not by how much actual power they consume, but by the potential of each of the individual LEDs to consume power if they're used at full capacity. They're not used at full capacity, and so the discrepancy. Buyer beware. 600w is 100 actual w. This leads me to more questions. 1. Is wattage even important as a concept in growing? 2. How can I measure what's important to measure - both in the spectrum and in the light output, or is all this just a case of being baffled by bullshit, an that very little of it matters. Plant a seed, water it, feed it, make sure it gets some light and wait. I'm no biologist, but I'm guessing that broadly speaking more light equates to better photosynthesis which equates in some way to healthier, better yielding plants. It seems that PAR is the value to measure or aim at, but I have no idea how. 3. What is the difference in yield between a 100w and a 600w light, assuming all else is the same?