You cant directly correlate between PAR and WPG. WPG was probably created as a rule of thumb that everyone can figure out easily to get in a ball park... PAR is a property of the spectrum of the bulb - impossibly to figure out without having a specific meter or at least accurate manufacturer supplied information (which most dont). For example two identical bulbs (48" T8 lets say) one is warm white and the other is daylight and both are the same 32W. So either would yield the same WPG. But PAR might be drastically different. Even the same bulbs (both 6500K for example) could be different PAR values if they are from different manufacturers.