On 9/23/19 2:47 PM, Jon Elson wrote:
On Sun, 22 Sep 2019 14:30:42 -0400, Larz wrote:

I recently installed a mercury vapor light fixture. It is a 125 W lamp
with integrated ballast in the housing. Today, I check the current with
a clamp ammeter on the 120 VAC/ 60 Hz line going into the housing. After
a 10 minute warm up, the current reads approximately 2.3 A AC. Not being
sure, I then wired a series multimeter in line for a moment and it too
read 2.3 A. Unfortunately, there is no PFC with this yard light, only
the bulb and ballast, so I don't think anything can be done.
However....

Without a Wattmeter, you have no idea what the actual power draw is.
Some of that 2.3 A is reactive current, at 90 degrees to the voltage, and
you are not billed for that. Measuring the current and voltage
separately, you only get the VA (volts * amps) which is NOT the power in
Watts.

Jon


Wow, I didn't know this or had forgotten. I am fully used to working
with DC, seldom AC I see digital plug in wattmeters on Amazon in the
$10-15. Would something like those be satisfactory? I really would
like to find out the true wattage.