> I'm trying to measure the average power consumed by a strobe light I
> have.  It is powered directly from the AC mains.
>
> ...
>
> P= IV, so this current curve on the scope * 120Vac (RMS) gives power
> consumed by the strobe.  Is this correct?

No.

> Can I just say "120V" when in
> fact the voltage is AC mains and varying millisec by millisec?

No.

> Should this be 180V ac?

No.

> Is the "right way" to do this estimation is to have one scope trace for
> current (voltage drop across 10ohm resistor) and another scope trace be
> the AC voltage coming in, and then you essentially timeslice into little
> boxes of a millisecond each, multiply I * V, and sum over one second?

Basically yes.  For arbitrary waveforms, you have to do the real integral.
Think about what would happen if plugged in a large capacitor instead of the
strobe.  RMS voltage and current might have similar values, but total power
would be zero.  That's because the integral of voltage*current over any one
cycle is zero.

For the special case of both current and voltage being sinusoids, you can
multiply the RMS values and adjust the result by the phase angle between
them.  However, this method is no use to you because the current isn't a
sinusoid.  There is no quick and dirty answer for arbitrary waveforms.


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