Power factor correction is an easy savings, if the bill includes a charge for peak VA demand. The best way is to get a recording meter. I borrowed one from a wholesaler and they did a calculation of the proper size capacitor bank and payback.
It's cheaper to install correction on the larger motors, because you can use the existing controls, but you need to do regular testing to make sure they don't fail. If you have VFDs in the building, the bank is better because you can install a filter. Harmonics are a problem with capacitors.
What kind of upgrade to lighting are you looking at?
