Section 9.5.1/Interior Lighting Power Allowance
ASHRAE 90.1 Section 9.5 and Table 9.5.1 establish maximum lighting power density by building type or space type.
The total installed interior lighting power must not exceed the interior lighting power allowance calculated using either the Building Area Method (Table 9.5.1) or the Space-by-Space Method (Table 9.6.1). The Building Area Method applies a single LPD (watts per square foot) based on the building type: 0.64 W/sf for offices, 0.72 W/sf for retail, 0.87 W/sf for schools. The Space-by-Space Method allows different LPDs for each space type and is more flexible for buildings with diverse space types. The total installed lighting wattage from the fixture schedule must be at or below the calculated allowance.
Why this section exists
Lighting typically accounts for 20-30% of commercial building electricity consumption. The LPD limits drive the adoption of efficient lighting technologies (LED, high-performance fluorescent) by capping the total power available. The 2022 edition LPD values reflect current LED technology capabilities. Designers can choose any combination of fixtures as long as the total power stays within the allowance. This performance-based approach allows design flexibility while ensuring energy efficiency.
What plan reviewers look for
Plan reviewers check the lighting compliance form for the calculation method (Building Area or Space-by-Space). They total the wattage from the lighting fixture schedule and compare it to the allowed LPD for the building or space type. They verify the square footage used in the calculation matches the floor plans. They check for exempt lighting (emergency, decorative within allowances) that may be excluded from the calculation.