On Thu, 17 Sep 2009 13:33:02 +0100, Bill R wrote:

My schoolboy
knowledge of a watt being voltage divided by amperage is obviously
wrong.
You're knowledge is correct for DC circuits and AC circuits with 100%
resistive load only.
When you start to add inductive and capacitative loads into an AC circuit
it affects the phase relationship between the voltage and current. Simple
measurement tools take no account of phase, just RMS values for current &
voltage so don't show true power consumed.

Bringing this back to the previous post, if the concept of power factor
really does effectively reduce the actual amount of power used why are
we being urged to replace tungsten bulbs in favour of the new bulbs.
The difference in wattage may be far greater overstated than the actual
difference.
The concept of power factor doesn't change the actual mount of power used
just how its measured.

BW