Par is a measure of light weighted to how plants use it. Lux is a measure of light weighted how we see it.
PPFD(umol/s/m2) is the unit of measurement for par. Similar to lux(lm/m2).
Someone else will have to chime in on par meters. Lux meters can be used with a known conversion rate, hps for example, .0122 rate, a 60,000lux reading would be 732ppfd.