# Lighting Power Density

LPD or UPD

Lighting Power Density formula is Watts/sqft

My question is watts= lamp watts of just the lamp( like T8 32w lamp) or " and this is where the problem starts" is it input watts(like T8-32w have a input watt of 28w) or is it lumens per watts

I just not sure which to use?

 tkrussell Posts: 9,673, Reputation: 3698 Senior Electrical & Lighting Expert #2 May 16, 2011, 01:26 PM

The total input watts of all lighting is needed to arrive at the LPD.

The published input watts of each ballast with the chosen lamp is needed. Do not simply add how many 32 watt lamps you have, you need the datasheet of the ballast that will be used, and the lamp that will be using that ballast.

Lumens per watt is only to show how efficient a particular light source is.

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