signbiz

How do you figure the wattage used per fixture? I am working with several customers trying to come up with a cost savings analysis from their current T-12 Magnetic Ballast fixtures and will be converting them over to T8 fixtures...and this poses the question about how many watts are being used in the new fixture...I can come up with the lamp wattage...54 watts per lamp but the ballast seems to be the question...how many watts total would this unit use with an energy efficient electronic ballast. Several manufacturers I questioned act like it is a great secret but one said to multiply the lamp wattage times the ballast factor and that will give you the total watts used per hour??? Is this true or do you take the voltage x amps = watts + lamp watts x ballast factor???

Anybody have an equation I input the numbers into to get my answers?

ralpha494

Use the numbers on the ballast. They have different numbers for the different lamps.

mcclary's electrical

The ballast gives you the energy used most likely in watts. Divide that by 1000. Then multiply by the hours used, that gives you kw-hrs. ex. 500 watt lamp running for 24 hrs uses 12 kw-hrs.

Lighting Retro

It's not a big mystery. The charts are all published by the major manufacturers, and you can look on them for exact wattage. First you have to know what voltage you are running, then look at a ballast chart like the one here:

You will notice the different ballast factors on the left side like .77 (considered Low), .87 Normal, 1.0 for the N+, and 1.15 or 1.18 for the high. Multiply those numbers by the total wattage of the lamps you'll be putting in, and you are pretty much there. Running 277 does make them slightly more efficient, but you'll be within a few watts total.

Here is also a handy link for "before" wattages that is fairly accurate and less cumbersome than most utility rebate program lists.

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MDShunk

Thanks, Lighting Retro. Nice post.

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signbiz

Thank you to everyone for all the information...it has been extremely helpful...

Lighting Retro

You are most welcome!

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jjdh

Illinois has adopted the IECC (International Energy Conservation Code) the code book with comentary contains charts with all this information. This information works 90% of the time. Also do a google search for COMcheck.You can download a DOE (Department of Energy) free program with instructions and educational information on IECC requirtements including lighting and controlls for interior and exterior lighting.