Ballast factor?

[mbrooke]

My understanding is this is how much the ballast will drive the lamp and in terms of lumen output. When looking for a replacement ballast, what ballast factor should I use? How does it effect lamp life? Energy efficiency?

 

[jcbabb]

My understanding is this is how much the ballast will drive the lamp and in terms of lumen output. When looking for a replacement ballast, what ballast factor should I use? How does it effect lamp life? Energy efficiency?

In very basic terms:
Li x bf = Lo

where Li = lamp rated lumens, bf = ballast factor, and Lo = lamp output lumens

And:
Lw x bf = Sw

where Lw = lamp wattage, bf = ballast factor, and Sw = system wattage

These formulas ignore the load inherent to the ballast as well as the efficacy of the fixture (some fixtures are more efficient at getting lamp lumens OUT), but they should get you what you need with respect to your question.

 

[mbrooke]

In very basic terms:
Li x bf = Lo

where Li = lamp rated lumens, bf = ballast factor, and Lo = lamp output lumens

And:
Lw x bf = Sw

where Lw = lamp wattage, bf = ballast factor, and Sw = system wattage

These formulas ignore the load inherent to the ballast as well as the efficacy of the fixture (some fixtures are more efficient at getting lamp lumens OUT), but they should get you what you need with respect to your question.

Thanks!

I do see ballasts with a BF greater than one, from the equation that means the tube is producing lumens over the rated wattage? :blink:

 

[GoldDigger]

Yes, it means that, and just as when you operate a motor at a service factor greater than one you need to know what the effects are on equipment life.

 

[mbrooke]

Yes, it means that, and just as when you operate a motor at a service factor greater than one you need to know what the effects are on equipment life.

But I don't know how that effects the tubes, over driving the lamp would force the cathodes to run hotter thus more emissive is boiled off?

 

[jcbabb]

I think it may depend on the lamp/ballast combo, but in general the lamp life is affected by the ballast factor.

 

[GoldDigger]

The lamp will run hotter, affecting the life of the phosphor. The cathodes will run hotter, increasing boil off of material and blackening of tube ends. It may also affect reduction of mercury concentration from chemical combination.

 

[Electric-Light]

Glad someone is showing interest in this rather than jumping on that decorative solid state thing shown in my avatar.

My understanding is this is how much the ballast will drive the lamp and in terms of lumen output. When looking for a replacement ballast, what ballast factor should I use? How does it effect lamp life? Energy efficiency?

The lamps are supposed to give you the rated life between 0.7 to 1.2 BF range.

Short answer. If you're replacing just a ballast or two, you use the N. For service stocks, you only need two types. 120-277 2N and 4N. These will cover for 17-32W T8 on 1 to 4 lamp applications. Most ballasts are approved to operate one less lamp than rated. You wouldn't be able to measure the efficiency difference for the system as a whole if you're spot replacing. If you're replacing a large quantity, you select carefully.

For high bays, you'll need the H ballasts or else you lose about 25% of output.

Your understanding is correct. You take the mean or design lamp lumen and multiply it by the BF. You tune the system by messing with lamp quantity , lamp type and ballast factor. BF isn't free lunch. If you lower or raise the output, the power use follows. Some ballasts shifts in BF a bit if you change the lamp type.

If your application needs and existing ballasts permit it, lamp tuning has a very quick payback and it will run laps around LE Decoras. Sometimes it's just a matter of using different lamps.