IECC Commercial Lighting Power and Controls
Summary
The commercial IECC caps the lighting power a building may install, in watts per square foot by space type or for the whole building, and requires automatic controls such as occupancy sensors, time switches, and daylight responsive dimming. Lighting design is checked against both the power allowance and the control requirements, so the lighting layout, fixtures, and controls are set together.
Cols
Scope
- Cites the IECC 2024, Section C405 (electrical power and lighting systems), by structure; the lighting power values could not be read from the 2024 text and are not listed. Always verify the adopted code edition and local amendments for the project jurisdiction
- ASHRAE 90.1 is an accepted alternative; its 2025 edition reorganized the lighting section and updated lighting power densities and controls
- Covers interior and exterior lighting for commercial buildings; residential lighting is in the residential provisions
- Emergency and exit lighting are exempt from the power calculation but covered by other codes
Terminology
- Lighting power density (LPD): installed lighting watts per square foot
- Lighting power allowance: the maximum connected lighting power for a building or space
- Building area method: one allowed LPD for the whole building type
- Space-by-space method: an allowed LPD for each room type, summed
- Occupancy sensor: a sensor that turns lights off when a space is empty
- Daylight responsive control: a control that dims or switches lights based on daylight
- Time switch: a scheduled control
- Interior lighting power: the sum of watts of fixtures in interior spaces
- Exterior lighting zone: a zone classification that sets exterior lighting allowances
- Lighting control narrative: the written description of how controls operate
Requirements
Power allowance
- Building area method: one LPD is applied to the whole building floor area, by building type, as a simple check
- Space-by-space method: each space type has its own LPD multiplied by its area; the total is the allowance and gives more credit for special rooms
- Installed power is the sum of fixture wattages, not the lamp ratings alone; luminaires with adjustable output are counted at their rated maximum or controlled value
- Exterior lighting has separate allowances by zone and application
- The 2025 edition of ASHRAE 90.1 reorganized lighting and updated the power densities and controls; jurisdictions on that standard use the new tables
Controls
- IECC, Section C405: automatic controls include occupancy sensors in specified space types, time switches or other automatic shutoff in other areas, daylight responsive controls in daylit zones, and manual controls for each space
- Control requirements are written by space type and the form of control (vacancy, occupancy, or automatic shutoff)
- Commissioning of controls may be required
Worked examples
Lighting allowance by area
An illustrative office floor of 10,000 sq ft with an illustrative allowance of 0.8 W per sq ft.
| Step | Calculation | Result |
|---|---|---|
| Allowed power | 10,000 × 0.8 | 8,000 W |
| Proposed | 300 fixtures at 22 W | 6,600 W |
| Check | 6,600 against 8,000 | Complies with 1,400 W to spare |
| Resulting LPD | 6,600 ÷ 10,000 | 0.66 W per sq ft |
Space-by-space
| Space | Area (sq ft) | Allowed (W per sq ft) | Allowed power (W) |
|---|---|---|---|
| Open office | 6,000 | 0.7 | 4,200 |
| Conference | 1,000 | 0.9 | 900 |
| Corridor | 1,500 | 0.4 | 600 |
| Lobby | 500 | 0.9 | 450 |
| Total | 9,000 | 6,150 |
The values are illustrative; the code tables supply the actual allowances.
Control check
| Space | Control |
|---|---|
| Private office | Occupancy or vacancy sensor, manual on |
| Corridor | Occupancy sensor or time switch |
| Perimeter zone with windows | Daylight responsive dimming |
| Lobby | Time switch or occupancy sensor |
Coordination
- Lighting designer: fixtures, layouts, and controls are chosen to the allowance, with a lighting calculation
- Architecture: ceiling heights, finishes, and reflectance affect required light levels and wattage
- Electrical engineer: the lighting circuits, panel schedule, and control wiring
- Daylighting: window and shading design set daylight zones that trigger control requirements
- Occupancy sensors and commissioning: specify sensor types, ranges, and testing
- Compliance form: COMcheck forms list fixtures and areas for the permit
Common issues
- Allowance exceeded in feature areas: accent lighting counted against the same allowance
- Controls omitted from the drawings: the lighting plan shows fixtures but not sensors
- Daylight zones missed: windows and skylights create zones that need controls
- Wattage changes in substitutions: a brighter fixture exceeds the allowance
- Mixed methods: the building area and space-by-space methods are not combined
- Exempt lighting misclassified: only listed uses are exempt
Standards
- IECC Section C405: commercial lighting and power
- ASHRAE 90.1: alternative commercial energy standard with its own lighting tables
- IES: illuminance recommendations used to set design light levels
Sources
- Data Driven AEC: IECC energy code requirements, https://datadrivenaec.com/insights/iecc-energy-code-requirements
- U.S. Department of Energy: Building Energy Codes Program, https://www.energycodes.gov/