Lighting Power Density Under NCC Section J

What You Need to Know

Every light in a commercial building has a power budget. The NCC caps how many watts you can use per square metre in each type of space. This cap is called the illumination power density (IPD). A standard office gets 4.5 W/m². A retail shop gets 14 W/m². A storeroom gets just 1.5 W/m². Go over the limit and your building fails Section J.

The NCC also tells you how to control those lights. Buildings over 250 m² must put 95% of all light fittings on a time switch or occupancy sensor. Lights near windows need separate switches from lights deeper in the room. These rules cut energy waste and are not optional.

• The total watts of all lights in a space (lamps, ballasts, drivers, and controls) divided by the floor area must not exceed the maximum IPD in Table J7D3a (NCC 2025, J7D3)
• Offices lit to 200 lux or more: maximum 4.5 W/m². Offices lit below 200 lux with task lights: maximum 2.5 W/m² (NCC 2025, Table J7D3a)
• Retail spaces (including museum and gallery sales areas): maximum 14 W/m² (NCC 2025, Table J7D3a)
• Storage areas: maximum 1.5 W/m². Wholesale storage at 160 lux: maximum 4 W/m² (NCC 2025, Table J7D3a)
• Corridors: maximum 5 W/m². Stairways: maximum 2 W/m² (NCC 2025, Table J7D3a)
• Toilets, locker rooms, and rest rooms: maximum 3 W/m² (NCC 2025, Table J7D3a)
• In buildings over 250 m², 95% of light fittings must connect to a time switch or occupancy sensor (NCC 2025, J7D4)
• Lights within the daylight zone near windows must be switched separately from lights away from windows (NCC 2025, J7D4)
• Motion detectors must turn lights off within 15 minutes of a space becoming unoccupied. In fire-isolated stairs, lights must dim to 30% or less after 15 minutes (NCC 2025, Specification 40)
• Adjustment factors reward control devices: motion detector in a room under 100 m² gives 0.6; daylight sensors with dynamic dimming near windows give 0.5. Maximum two factors per area (NCC 2025, Table J7D3b)
• Warm-colour lights (3500 K or below) get a factor of 0.8. Cool lights (4500 K or above) get 1.1. High-CRI lights (CRI 90+) get 0.9 (NCC 2025, Table J7D3c)

Take a 500 m² open-plan office lit to 320 lux. The IPD limit is 4.5 W/m². That gives you a total lighting power budget of 2,250 W for the entire floor plate. With modern LED panels rated at 30 W each covering about 8 m², you would use roughly 63 fittings drawing 1,890 W. That sits under the 2,250 W cap with room to spare.

Now add occupancy sensors to every zone under 100 m². The adjustment factor of 0.6 means you divide the maximum IPD by 0.6, which raises your effective cap to 7.5 W/m². That headroom lets you use higher-output fittings or add accent lighting without exceeding the budget.

But those sensors come with rules. Each one must detect a person before they walk 1 m into the space. The lights must shut off after 15 minutes with no one present. These are not suggestions - Specification 40 sets them as hard requirements.

For a retail fitout, the 14 W/m² allowance gives much more freedom. A 200 m² shop gets a 2,800 W budget. That covers track lighting on merchandise, general ambient lighting, and feature displays. But display lighting must be on a separate switch from general lighting. Any display zone pulling more than 1 kW needs a time switch.

Small rooms create a different problem. In a room with a low aspect ratio (under 1.5), light bounces off walls less and you need more fittings to hit the same lux level. The NCC accounts for this with a room aspect ratio adjustment. You divide the IPD limit by a factor calculated as 0.5 + (aspect ratio / 3). For a small meeting room with a ratio of 1.0, the factor is 0.83, raising the effective limit from 5 W/m² to about 6 W/m².