Luminaire wattage

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john37

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How do you determine the actual wattage of a fluorescent fixture with an electronic ballast? Not sure how to implement the ballast factor and power factor when trying to get the actual wattage of the luminaire. Thanks.
 
The actual "wattage" = total watts of all the lamps. If you want Volt-Amps, then you have to deal with the additional calculations involving things like power factor.

Two-bulb fixture, 32 watts per bulb = 64 watts.
 
Think fishing:

Power = Watts
I = Amps
Energy = Volts
Resistance= Ohms

OR "PIER WAVO"

W=AV <
or
P=IE
 
As far as I recall, ballasts are usually labeled with the line current or VA, sometimes with different currents for different tubes.
 
I add 5% for ballast factor on calculating my loads for Flourescent electronic ballasts.
3-32 W T8's = 96Watts x 1.05 = 100.8 watts for a typical troffer. I dont worry about the power factor when designing for the lighting.

hope this helps.
 
When using electronic ballasts the input power ratings are significantly less than a standard ballast (to produce the same lumen output as controlled ballasts in laboratory conditions). My standard fixtures are relatively inefficient, but still rated 112 VA and 58 VA (4 and 2 lamp T-8's, .99pf). Sometimes slightly different, the manufacturers' photometric (*.ies) files include this data. You do not add up the wattages of the individual lamps. This is a bad assumption. Supprisingly, a high(er) efficiency 2-F32T8 ballast, with .98pf, is as low as 47W, 75% of what one would regularly think. Check out Advanced ballasts' website.
 
Thanks everyone for their input.
What I'm actually trying to figure out is how to calculate the VA of a fluorescent light fixture in order to fill out a panel schedule.
When I look in the Advance catalog for a standard instant start 2 lamp 32W T8 ballast it states the following:
Input power ANSI (watts) 58
Ballast Factor 0.87
Line Current (Amps) 0.49

Please explain how I calc it to get the VA. Thanks.
 
john37 said:
Input power ANSI (watts) 58
Ballast Factor 0.87
Line Current (Amps) 0.49

Please explain how I calc it to get the VA. Thanks.
Click to expand...
Sure:

va = w (closely enough for this case)

Or, another way:

W = V * A
W = 120 * 0.49
W = 58.8
W = va

Make it easy on yourself by rounding. The label shows .49A, or 1/2 amp. That's 60 watts (@120v) in English.
 
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