Lighting Load Calculator

Lighting Load Guide for AS/NZS 3000 and AS 1680

Lighting load calculation determines how much electrical capacity a lighting installation requires and how that load should be distributed across circuits. This is a fundamental step in any electrical design because it drives circuit count, cable sizing, circuit breaker selection, and ultimately the contribution to the building's maximum demand. AS/NZS 3000 (Wiring Rules) sets the rules for circuit loading and outlet counts, while AS 1680 (Interior and Workplace Lighting) defines the illumination levels that the lighting system must achieve.

This calculator takes your luminaire specifications, the number of fittings, and the floor area being served, then computes the total circuit load, the number of circuits required, and the watts per square metre (W/m squared) lighting power density. It flags any circuits that exceed the maximum current rating and checks the lighting power density against typical benchmarks for the space type.

Key concepts

• Driver input wattage, not LED chip wattage. LED luminaires consume more power at the supply terminals than the LED chips alone draw, because the driver has conversion losses (typically 85% to 95% efficient). A "40 W LED panel" might draw 44 W from the supply. Always use the driver input wattage from the manufacturer datasheet for circuit load calculations. Using the LED chip wattage will underestimate the load and can result in overloaded circuits.
• Circuit limits under AS/NZS 3000. Lighting circuits are typically protected by a 10 A or 16 A circuit breaker. At 230 V, a 10 A circuit can supply a maximum of 2,300 W. AS/NZS 3000 also limits lighting circuits to 20 outlets (points of attachment) per circuit in some configurations. The practical limit is usually the current capacity rather than the outlet count when using modern LED luminaires.
• Watts per square metre (lighting power density).W/m squared is the total installed lighting wattage divided by the floor area. This metric is used by the National Construction Code (NCC) Section J to set maximum allowable lighting power density for energy efficiency compliance. Typical values for modern LED installations are 5 to 8 W/m squared for offices, 8 to 12 W/m squared for retail, and 3 to 5 W/m squared for corridors and storage areas.
• Emergency lighting contribution. Luminaires with integral emergency batteries draw a small continuous charging current (typically 2 to 5 W per fitting) on top of their normal operating wattage. This charging load must be included in the circuit load calculation. During a mains failure, these luminaires switch to battery power and the circuit load drops, but the circuit must be sized for the normal operating condition including the charge current.

Common scenarios

• Open plan office fit-out. A 500 m squared open plan office requires approximately 400 lux at desk height per AS 1680.1. Using 36 W LED panels at 130 lumens per watt, the designer needs roughly 42 luminaires (total 1,512 W, or about 3.0 W/m squared). This fits comfortably on a single 10 A circuit, but for maintenance flexibility and to avoid a total blackout from one tripped breaker, it is standard practice to split the load across two or three circuits covering different zones of the floor plate.
• Warehouse or industrial shed. A 2,000 m squared warehouse with 8 m mounting height needs high bay luminaires producing enough lumens to achieve 200 lux at floor level. Using 200 W LED high bays, the designer might specify 40 fittings (total 8,000 W, or 4.0 W/m squared). At 230 V, this is approximately 34.8 A total, requiring a minimum of three 16 A circuits or four 10 A circuits. Cable runs to high bays are long, so voltage drop must be checked alongside the load calculation.
• Retail tenancy with feature lighting. A retail fit-out combines general ambient lighting (recessed downlights or panels), accent lighting (track spots on displays), and decorative feature lighting (pendant fixtures, LED strip). Each type has different wattages and control requirements. The lighting load calculation must account for all three categories, and circuits are often separated by lighting type so that accent and feature lighting can be switched or dimmed independently from the general lighting.