scientific question for advanced electricians

punkin · Apr 14, 2017

Does anyone know or have actually tested the amount of power a fluorescent light takes?

So if I have a 58 watt tube, will the light fitting including the tube take 58 watts or is it more because of the ballast?

I'm wondering because the ballast gets warm, so say if that takes aprox 10 watts and the tube is 58 watts, therefore in total its about 68 watts it consumes in total??
Or is it aprox 10 watts for the ballast & 48 watts for the tube & total becomes 58watts??

Which on is it, has anyone done the testing??

cheers
Pete

SparkyChick · Apr 14, 2017

I've not tested, but I believe the total consumption of a fitting is the nominal tube power rating plus losses in the ballast. Run one up and clamp the line get a current reading and work it out from there.

snowhead · Apr 14, 2017

Yes, just now.

Maxed out at 66.4 watts after 4 minutes

punkin · Apr 14, 2017

Nice one snowhead,

I learned at collage that if you add a capacitor, it reduces current and helps correct the power factor, does your fitting have the capacitor too?

Don't know if that helps with the power consumption also???

Wilko · Apr 14, 2017

Hi - sounds a simple enough question doesn't it ? Maybe 10% for a guesstimate (no warranty

) because there's a bit in this. If you'd like a bit of reading, perhaps check out this article.
http://www.etsii.upct.es/antonio/html_der/papers/Ballasts.pdf

Edit : hah - just seen your power meter value ...

Darkwood · Apr 14, 2017

The marked value on a lamp is the nominal rated power consumption, due to manufacturing processes and variants like lamp colour etc their is a lamp efficiency that needs to be applied to be exact but been an unknown variable it can only be estimated based on lamp standards and compliance.
As mentioned there is also the ballast losses to take into account which is an additional quantity.

Also been an inductive load a factor of 1.8 will be applied when calculating cable size, switch, fuse rating etc.

snowhead · Apr 14, 2017

Yes capacitor included.
Capacitor disconnected and measured watts increased over the same time as before.
Capacitor reconnected and watts immediately went back to 66.4

punkin · Apr 14, 2017

Had a very quick scan through the document Wilko and seems like it also depends on the ballast, looks like electronic ballast will reduce the power to less than 58 watts in some cases.

That answers my question snowhead, so the choke type ballast defiantly takes extra power.

cheers
Pete