# Lighting Power Density Calculation



## windseaker (May 14, 2011)

LPD = watts/sf2

But what is kind of watts here "total"
??
Say two T8 lamp 32Ws =64 watts but what about ballast watts or is it lumens /watts??

or fixture watts ( which is ?)


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## oldtimer (Jun 10, 2010)

windseaker said:


> LPD = watts/sf2
> 
> But what is kind of watts here "total"
> ??
> ...


 I would assume it is TOTAL watts.


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## Jmohl (Apr 26, 2011)

Lightman might want to weigh in on this one...... Seems to me that the formula you have is over simplistic. Lumen output and coverage for one type luminaire will vary greatly from others, also mounting height, etc... :confused1:


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## windseaker (May 14, 2011)

Still do not know what "total watts" is


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## Jmohl (Apr 26, 2011)

Two tube f32t8 fixture= 64 total watts. Again, I don't see the value. 64W of light from fluorescents at say 10ft mounting gives you a totally different light level on the floor than say 60 watts of incandescent. If the equation factored in lm/w (efficacy) and CRI, then that would have some meaning....:huh:


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## Cletis (Aug 20, 2010)

*Density*

Pretty sure it's only bulb wattage. Ballast don't put out light. 

Yes, 50 watts per sq ft at floor level on a meter is seen totally different by the eye depending on type of bulbs, spectrums, flood or point source, etc...


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## bobelectric (Feb 24, 2007)

You need to use Lumens,not watts.


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