How do I caclulate the total watts consumed by a T8 fluorescent light fixture? It has (6) 28w bulbs with two ultra high electronic ballasts.

Thanks,

John

Ballast pf or efficiency?

P = Power * Efficiency

Efficiency can be written as pf or power factor.

So if both ballasts ar 85% efficient.

P = 6 tubes * (1/0.85) * 28 W

The ballast efficiency can vary from about 85 to 95% or 0.85 to 0.95

The value needed is "Ballast Factor" not power factor.

An excerpt from
Light Guide: Fluorescent Ballasts

Ballast Factor
One of the most important ballast parameters for the lighting designer/engineer is the ballast factor. The ballast factor is needed to determine the light output for a particular lamp-ballast system. Ballast factor is a measure of the actual lumen output for a specific lamp-ballast system relative to the rated lumen output measured with a reference ballast under ANSI test conditions (open air at 25 degrees C [77 degrees F]). An ANSI ballast for standard 40-watt F40T12 lamps requires a ballast factor of 0.95; the same ballast has a ballast factor of 0.87 for 34-watt energy saving F40T12 lamps. However, many ballasts are available with either high (conforming to the ANSI specifications) or low ballast factors (70 to 75%). It is important to note that the ballast factor value is not simply a characteristic of the ballast, but of the lamp-ballast system. Ballasts that can operate more than one type of lamp (e.g., the 40-watt F40 ballast can operate either 40-watt F40T12, 34-watt F40T12, or 40-watt F40T10 lamps) will generally have a different ballast factor for each combination (e.g., 95%, <95%, and >95%, respectively).
Ballast factor is not a measure of energy efficiency. Although a lower ballast factor reduces lamp lumen output, it also consumes proportionally less input power. As such, careful selection of a lamp-ballast system with a specific ballast factor allows designers to better minimize energy use by "tuning" the lighting levels in the space. For example, in new construction, high ballast factors are generally best, since fewer luminaires will be required to meet the light level requirements. In retrofit applications or in areas with less critical visual tasks, such as aisles and hallways, lower ballast factor ballasts may be more appropriate.



The simplest method is to refer to the manufacturers datasheet for input watts for a particular lamp and ballast system.

With the published input watts, you can then calculate the BEF, Ballast Efficiency Factor, which needs the input watts to complete the calculation:

http://www.lightingassociates.org/i/...f_Ballasts.pdf


Only the manufacturer can tell what each ballast will draw for input watts.

Any field calculations will be close but not accurate.


I do not see how using the Power Factor is helpful in calculating input watts:

STANDARD, Ballast Lamps

Thanks tk. That just makes the calcs a bit more interesting.

Quote:

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Originally Posted by KeepItSimpleStupid

Thanks tk. That just makes the calcs a bit more interesting.

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LOL!! Yes it does!

I love our calculations! It presents reality. Reality that says: We know more than just hooking-up a blk and what wire<----which many believe is the only thing our job entails!!

Just to break the monotony, sometimes I like to splice black and white.

And sometimes I did it because I was in a hurry and not paying attention.

Really sucks troubleshooting a new circuit thinking there is a real problem just to find that I was the problem.

Quote:

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Originally Posted by tkrussell

Just to break the monotony, sometimes I like to splice black and white.

And sometimes I did it because I was in a hurry and not paying attention.

Really sucks troubleshooting a new circuit thinking there is a real problem just to find that I was the problem.

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LOL! Yeah, I did this before. But it was an embarrassing moment for me when I turned the power on, and the customer and I heard a boom. :eek:. Yet, we laughed it off, and I gained more work! :)

vtalin, I'm curious... which ballast did you have that did not tell you what the total consumed wattage was?