# Wattage Question...



## ralpha494 (Oct 29, 2008)

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


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## McClary’s Electrical (Feb 21, 2009)

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.


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## Lighting Retro (Aug 1, 2009)

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 (Jan 7, 2007)

Thanks, Lighting Retro. Nice post.


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## signbiz (Sep 3, 2009)

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


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## Lighting Retro (Aug 1, 2009)

You are most welcome!


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## jjdh (Sep 8, 2009)

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.


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## Electric_Light (Apr 6, 2010)

signbiz said:


> 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?


This is from Advance models: 
277v 2 lamps 86W if they're using high CRI F40T12 40W lamps. 72W if they're using cool white 34W F40T12/ES. 
94 91 

4 lamp fixtures will almost always have 2 x two lamp ballast. 

F32T8 56W/2lamp or 112W for 4 lamp. 

Saving of 15W/lamp for F40T12 to F32T8 or 8W/lamp for F40T12/ES to F32T8 would be good estimates. You might actually save this much power, but with a T8 conversion, you usually lose some light, because T12 mag ballasts run the lamps at ~95% BF while T8 "regular output" ballasts run the lamps at 88%. 

These figures take into ballast factor. Lamps used were SPEC35 vs TL735 based on MEAN lumens, not initial. 

2710lm/lamp for F40T12 63LPW
2300lm/lamp for F40T12/ES 64LPW 
2400lm/lamp for F32T8 or 85LPW 
2710lm/lamp for F32T8 using GE N+ ballast but raises power to 31W/lamp

You can make the numbers better if you use premium efficiency ballast (GE MAX ULTRA N) with premium efficacy lamps (Philips F32T8/TL835 ADVANTAGE)... but to maintain the system efficacy it requires the customer to use the premium lamps. 
26.5W/lamp, 2610 lumen per lamp. ~98LPW 

If it turns out the client's location is over-lit, you can go with premium efficiency low output ballast together with premium lamps. The install and re-lamp cost will be high, but you'll break 100LPW and increase watts/lamp saved even more


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