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Lighting: Calculating Efficacy with power factor

Lighting: Calculating Efficacy with power factor

Lighting: Calculating Efficacy with power factor

(OP)
Hi, Im trying to calculate efficacy for a lighting assignment, I know the equation for efficacy is Lumens divided by Power but this question includes a power factor rating, how do I incorporate this into the equation?? would i need to multiply Power (Watts) by power factor??

RE: Lighting: Calculating Efficacy with power factor

Look at the technical specs for the ballast.  Find the VA input and efficiency.  Then look at the lamp data and get the lumens/watt data.

You have to account for the ballast losses. This should be provided with the ballast data.

 

David Castor
www.cvoes.com

RE: Lighting: Calculating Efficacy with power factor

(OP)
Thanks, but the only values i have for this task are a 2x26 watt luminaire with a power factor of cos 0.98 and a lumen output of 3600 lumens,  

RE: Lighting: Calculating Efficacy with power factor

Power multiplied by power factor is a meaningless quantity.  You already have lumens and watts.  Can you figure out the next step?

RE: Lighting: Calculating Efficacy with power factor

As magoo says, if you already know the watts, the power factor is not needed to compute lumens/watt.

 

David Castor
www.cvoes.com

RE: Lighting: Calculating Efficacy with power factor

Looking at it another way; if all you had was voltage and amperage, and you WANTED to know the watts, then you would need the power factor. But if you ALREADY have the watts, you don't need to use pf again.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
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RE: Lighting: Calculating Efficacy with power factor

I suppose that if someone wanted the efficacy expressed in lumens/VA instead of lumens/watt, you could multiply the lumens/watt value by the power factor. Even with a low power factor, I could only see anyone caring if there were a huge number of these in an industrial facility that gets charged for poor power factor

In your case, it would only make a 2% difference anyway.

RE: Lighting: Calculating Efficacy with power factor

Just to finish beating this horse, the watt consumption data for the lamps probably does NOT include the ballast losses, which can be significant.  

 

David Castor
www.cvoes.com

RE: Lighting: Calculating Efficacy with power factor

(OP)
cswilson yes i do beleive that is what im trying to achieve (lumnes per VA), its a small difference but  but this is what ive been told to to do; calculate efficacy and incorporate the power factor for the ballast losses, thanks guys much apreciated

RE: Lighting: Calculating Efficacy with power factor

Just curious, what's the value in knowing lumens/VA?

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
  
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies  

RE: Lighting: Calculating Efficacy with power factor

Power factor has nothing to do with the ballast losses.

I could see you using the lamp watts and the ballast efficiency to calculate incoming watts and then use the power factor to calculate incoming VA to know how much current the light will draw.

You really don't seem to know what you want here. Maybe you should take a step back and figure out what numbers you need and why you need them.
 

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