PFC for Neons

Uncorrected neon transformers are usually 50% power factor. To correct them
for 90% power factor add a capacitor calculated as follows:

    For 120 volts    c uf = .079 V A     
    For 240 volts    c uf = .020 V A
    V = neon secondary volts     A = neon secondary amps
The factors       K1 = sin(arccos(LPF)-sin(arccos(HPF))
                  K1 = .43 for 50% to 90% power factor

For 120 volts     K2 = (.43 x 10^6)/(6.283 F V)           F = 60 Hz 
                  K2 = (.43 x 10^6)/(377 x 120^2) = .079
For 240 volts     K2 = .0198 or .02

Example:   Neon 15000 volts  60 ma  120 volts  60 Hz

           C = .079 x 15000 x .06 = 71.1 uf 
Note that power factor correction is normally used to reduce your electric
power bill.
This has little value with Tesla coils because they are not operated for
very long.
I do not believe that paying more for a HPF neon or adding a capacitor is
worth it.
Also adding a capacitor in parallel with the primary neon winding can lead
to resonance problems as indicated by some of the Tesla List letters.

Power factor is not efficiency. The efficiency of typical neons is about 96%
for both low and high power factor. A higher power factor means less current
from the utility but the current saved is reactive current which does not
affect the meter. A wattmeter only registers watts. 

Efficiency is based only on watts, not reactive VA. The money you save with
HPF is based on other factors. If you are confused, you are not alone.