If by PF here you mean the lamp discharge PF, 0.77 looks too low. 0.85..0.9 is normal. Could it have been calculated before with some error there ?
If you mean PF of the entire circuit, that would not appear in the equation at all (the sqrt( voltages ) in the formula already takes care of it). And 0.77 is way too high for a discharge lamp without capacitor
Also, by Zbal do you actually mean Zbal or Xbal, and how did you find it ?