Here the new version 1.1 of the plug-in with the feature you requested:
http://www.sweethome3d.com/plugins/CopyAsNewFurniturePlugin-1.1.sh3p
The new piece of furniture copied in the clipboard is considered itself as some kind of light with a power attribute, as soon as the copied items contains at least a light. The power of this piece is equal to the max power of all the lights it contains.
Happy new year 2011!
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Emmanuel Puybaret, Sweet Home 3D creator
