Lighting power density (LPD) is the installed lighting power of a space divided by its floor area, usually stated in watts per square foot.
Energy codes and standards, such as ASHRAE 90.1 and the International Energy Conservation Code, set maximum LPD values by space type, including parking garages. The limits have fallen steadily as lighting technology has improved, and garage limits are now a fraction of a watt per square foot. Codes also require automatic controls, such as occupancy-based dimming and daylight response near openings.
In parking facilities
- LED fixtures make current limits achievable while still meeting recommended illuminance. See LED lighting.
- Controls cut energy further by dimming unoccupied areas and perimeter zones in daylight. See adaptive lighting.
- LPD measures installed power, not hours of use; controls reduce the energy actually used.
The Parkonomics view
Meeting the LPD limit is the floor, not the goal. The best-performing garages pair efficient fixtures with controls that keep most lights dimmed most of the night while still lighting people where they are.
Related terms: LED Lighting, Adaptive Lighting, Illuminance, ASHRAE