Lighting Power Density (W/ft²) & Energy Code Calculator

How it works

LPD = total input watts ÷ floor area; allowed watts = allowance × area; annual kWh = watts × hours ÷ 1,000; controls saving = kWh × credit %

Energy codes limit how much lighting power a building may install per square foot, either as a whole-building number by building type or space-by-space with a different allowance for each room function — open offices around 0.6 W/ft², retail about 1.0, corridors 0.4, parking garages 0.15 in ASHRAE 90.1-2019 and the IECC that references it (California Title 24 is tighter still). LED efficacy has made compliance easy — a well-designed office now installs half its allowance — and the emphasis has shifted to mandatory controls: occupancy or vacancy sensors, automatic daylight dimming near windows, and time-of-day shutoff, which together cut actual lighting energy by a further third to a half. Lighting power also becomes heat that the cooling system must remove, so every lighting watt saved saves a little more in summer.

Worked example

30 fixtures at 32 W in a 1,200 ft² open office give 0.80 W/ft² — 31% over the 0.61 W/ft² allowance; the space allows 732 W, so 22 such fixtures (or 30 at 24 W). At 3,000 hours the 960 W installed uses 2,880 kWh — $403 a year — and occupancy sensors would save about $100.

Frequently asked questions