The energy model requires a lighting power density for the proposed building, but neither the EPA Simulation Guidelines nor ASHRAE Std. 90.1, Appendix G specify a minimum light output level. Consequently, a very large space could be significantly underlit and take significant credit for a low lighting power density. Does USGBC have a minimum requirement for lighting levels?
Any spaces with no lighting or insufficient lighting output should be modeled with the default lighting power density levels (e.g. 2 watts/sq.ft. in-units). USGBC does not have a specific definition for "insufficient lighting", but if the occupants could reasonably be expected to need floor lamps, the space should be considered insufficiently lit. If the project team is looking for a standard, the IESNA Lighting Design Guidelines should be reviewed. These guidelines specify at least 5 footcandles for general lighting.
Updated 10/1/13 for rating system applicability.