Section C405.1/Lighting Power Density
IECC C405 covers interior and exterior lighting power density limits and automatic lighting control requirements.
The total connected interior lighting power must not exceed the values in Table C405.3.2 using either the building area method (single LPD for the whole building type) or the space-by-space method (different LPD for each space type). For offices, the building area LPD is typically 0.82 watts per square foot. For retail, 1.06 watts per square foot. Interior lighting must also include automatic controls: occupancy sensors, daylight responsive controls in daylit zones, and automatic time switches.
Why this section exists
Lighting accounts for 15-30% of commercial building electricity use. The LPD limits ensure that buildings use reasonably efficient lighting systems. Modern LED technology makes compliance straightforward for most designs, but the automatic control requirements are where most plan review comments occur. Controls reduce energy waste from lights left on in unoccupied spaces and from artificial lighting in daylit areas.
What plan reviewers look for
Plan reviewers check the lighting power calculation (total connected watts divided by floor area) against Table C405.3.2. They verify that occupancy sensors are shown on the reflected ceiling plan for the spaces that require them (private offices, restrooms, conference rooms). They check for daylight responsive controls in spaces within 15 feet of fenestration. They also verify that exterior lighting complies with the exterior LPD limits.
Common violations
Related IECC requirements
Section C405.2 covers lighting controls in detail. Section C403 covers HVAC systems. Section C408 covers commissioning requirements for lighting controls. ASHRAE 90.1 Section 9 provides equivalent lighting power requirements.