LPD lighting power Density

[windseaker]

Lighting power density = watts/ sf2, but what watts? is it total watts like 2lamps at 32 watt= 64 watts or is it 2lamps at 32 watts plus BF( ballast factor) (.88) = 56.32 watts or is it total lumens per watts ?

 

[Electric-Light]

Lighting power density = watts/ sf2, but what watts? is it total watts like 2lamps at 32 watt= 64 watts or is it 2lamps at 32 watts plus BF( ballast factor) (.88) = 56.32 watts or is it total lumens per watts ?

It's the permissible energy use per square foot on lighting energy. So, if the luminaire input wattage is 53W (General Electric GE232MAX-N, 0.87) and if the limit is 1W/sqft, then you can only have that fixture every 53 square foot ish.

Energy codes are tightening but required FC level in today's design isn't as high as it was before for a lot of space use applications.

 

[windseaker]

So your saying it is the catalog "input watts"?

Do you know have that is calculated?

 

[Electric-Light]

So your saying it is the catalog "input watts"?

Do you know have that is calculated?

It depends on the lamp you use. F32T8 will cause the fixture to use more power than F32T8/25W. The ballast or fixture data sheet should tell you the input wattage with the lamps installed. The fixture data may only give you one for the primary lamp type. Same model fixture don't necessarily have same model ballast, so if you want to use reduced wattage lamps and want to know the input watt you'll have to pop the cover off and get the ballast information, then get ballast datasheet.

For standard output (~0.87 BF) two lamp T8 it can range from 53-60W with two F32T8, depending on ballast efficiency. You have to refer to datasheet on this one.

For T8 electronic system, if you allocate lamp wattage x lamp number(4 lamp 32W T8 = 128W) , you'll be fine except for high ballast factor system, but you end up over-allocating permissible watts to each fixture and this isn't a good idea if you need to use every bit of it to get the lighting level you need.