Hi there. I posted some pics of my first post top fixture a few days ago and I discovered that the ballast was disconnected and bypassed to run a CFL lamp (lame lol) and after some testing I found the ballast to be in working condition

I jumped on Ebay to find a 75 watt MV lamp and ended up purchasing a Philips NOS bulb, pics will be posted.

After wiring the ballast and lighting up this 75 watt DX coated MV lamp I'm very surprised at how bright this set up is.

I measured the current between the lamp and the ballast and my reading stabilized at .71 amps, This seems high to me because after multiplying this by my line voltage (121v) I'm getting a wattage reading of 85.91 watts.

Is this ballast over driving this lamp?

Thanks.
 

Not at all.

First assume you are really talking about the lamp circuit, so lamp arc voltage and arc current, not the primary current. Otherwise there are ballast losses and I don't believe these would be just 6W, I would expect around 15W or so.

Don't forget there is quite strong mismatch in the waveform shape between the arc voltage (early rectangular, an equilibrium on the electric field generating the free ions and their recombination afterwards tends to maintain the arc voltage really constant) and current (sinewave or even more like triangular - due to the partial shunt saturation) and even a slight phase shift between the voltage and current (because the ionization level has some inertia behind the current; but that uses to be really very small, just in the form of a zero cross reignition overshoot). That mismatch means the real transferred power is less than just multiplying the voltage and curent (power factor is less than unity).
With a sinewave current the power factor will be 2*sqrt(2)/Pi=0.9 (neglecting the phase shift, as that is really small).
So with 121Vrms across the lamp and 0.71Arms arc current, the real power delivered to the lamp is just around the rated 75W (non distorted sinewave current would mean 77W, more distorted triangular current would mean about 74W).

Not at all.

First assume you are really talking about the lamp circuit, so lamp arc voltage and arc current, not the primary current. Otherwise there are ballast losses and I don't believe these would be just 6W, I would expect around 15W or so.

Don't forget there is quite strong mismatch in the waveform shape between the arc voltage (early rectangular, an equilibrium on the electric field generating the free ions and their recombination afterwards tends to maintain the arc voltage really constant) and current (sinewave or even more like triangular - due to the partial shunt saturation) and even a slight phase shift between the voltage and current (because the ionization level has some inertia behind the current; but that uses to be really very small, just in the form of a zero cross reignition overshoot). That mismatch means the real transferred power is less than just multiplying the voltage and curent (power factor is less than unity).
With a sinewave current the power factor will be 2*sqrt(2)/Pi=0.9 (neglecting the phase shift, as that is really small).
So with 121Vrms across the lamp and 0.71Arms arc current, the real power delivered to the lamp is just around the rated 75W (non distorted sinewave current would mean 77W, more distorted triangular current would mean about 74W).

Okay and sounds good. I thought maybe the lamp was being over driven because it is so bright! Seems brighter than a new 100w MV lamp would emit!