Lighting Load Calculator

Parameters

Every field this calculator exposes, what it means, the range it accepts, and the traps worth knowing before you rely on the answer.

Luminaire schedule, one row per type

Add one row per luminaire type. Rows are grouped by type, wattage and quantity, and each row is multiplied by a control gear factor before being summed. The label and the per row factor appear once you turn on "Per row label and control gear factor" in Advanced options.

Luminaire typeLED, fluorescent, halogen, HID or other

Selects the control gear factor applied to that row: LED 1.00, halogen 1.00, fluorescent 1.10, other 1.10 and HID 1.15. These are indicative allowances for ballast and driver losses, not values transcribed from a standard or a datasheet. If your manufacturer already quotes a circuit input wattage that includes the driver, choose LED or halogen so the factor stays at 1.00 and you do not double count the losses.

Wattagewatts per luminaire

Rated wattage of a single fitting. Accepts 1 to 10,000 watts. Gotcha: for LED fittings this should be the driver input wattage from the datasheet, not the light engine or chip wattage. A fitting sold as a 40 watt panel commonly draws 44 watts at the terminals.

Quantitywhole number

Number of identical fittings in that group. Must be a positive whole number; the form accepts 1 to 1,000. Quantities are also summed as lighting points for the points per circuit check.

Row labeltext, optional

Free text description for that row, for example "Level 2 open plan panels". It carries through to the breakdown table and into the working, so a schedule with several rows of the same type stays readable.

Control gear factor0.5 to 3, optional

Overrides the type based factor for that row only. Use it when the datasheet gives a circuit input wattage (set 1.00 so the driver loss is not counted twice), or when you know the real ballast loss for a specific fitting. Blank falls back to the type factor.

Circuit fields

Supply voltagevolts

Voltage used to convert watts to amperes. Default 230. The form accepts 100 to 415 volts. One voltage applies to every luminaire and every circuit; there is no mixed voltage option.

Circuit breaker ratingamperes

Rating of the protective device on each lighting circuit, typically 10 or 16 amperes. On its own it is still just the sanity check that your max circuit load is not larger than the breaker. Set a breaker loading factor in Advanced options and it becomes the thing that actually calculates the circuit split.

Max circuit loadamperes

The design current you are prepared to put on one circuit. With no breaker loading factor set, this is what drives the circuit count. With one set, it acts as a cap on the breaker derived figure, so the per circuit limit is the smaller of the two. The form defaults to 10 amperes against a 16 ampere breaker.

Room areasquare metres, optional

Floor area served by the lighting. Leave it blank to skip the density calculation entirely. When it is filled in, the watts per square metre result appears together with the target for the premises type you chose and the margin against it. The target is no longer a fixed office number; it follows the premises type unless you override it.

Emergency lighting requiredcheckbox

Adds the AS 2293 reminder note to the results, and warns if you have ticked it without entering any emergency or exit counts. The counts themselves, not this checkbox, are what add load.

Advanced options

Everything below is optional and hidden behind the Advanced options block. Leave the whole block alone and the calculator behaves exactly as the basic form describes.

Aggregate connected loadwatts, optional

A lump connected total for lighting you have not scheduled row by row. It is added to the schedule sum and shown as its own "aggregate" row in the breakdown. You can use it on its own with no schedule rows at all, which is the quick path when you only have a total off a drawing. Gotcha: aggregate watts contribute zero lighting points, so they do not affect the points per circuit check.

Premises typenine options across Appendix C Columns 1 to 3

Drives two things. First, the AS/NZS 3000 Appendix C load group (a) lighting diversity, which differs between Column 2 premises (multiple domestic, blocks of living units) and Column 3 premises (offices, shops, hotels, hospitals, schools, industrial, warehouses). Second, the watts per square metre target the density result is judged against. Default is Office, Column 3, diversity 1.00, target 20 watts per square metre, which reproduces the old behaviour. Gotcha: the diversity values and the density targets in this list are indicative planning figures pending verification, not transcriptions from the published standard.

Diversity factor override0 to 1, optional

Replaces the premises type diversity with your own number. Use it when you have a project specific demand agreement. Blank uses the premises figure.

Spare capacitypercent, default 0

Allowance for future luminaires, applied to the connected load before diversity. 10 percent on a 2,000 watt connected load gives a 2,200 watt figure before any diversity is applied.

Power factor0.1 to 1, default 1.0

Load power factor used to convert watts to amperes. At the default of 1.0 the current is simply watts divided by volts, which is what this calculator used to assume. Cheap LED drivers commonly run 0.5 to 0.9 and the calculator warns below 0.8, because a 0.5 power factor doubles the circuit current for the same wattage.

Supply arrangementsingle phase or three phase

Single phase uses I = P / (V x pf). Three phase balanced uses I = P / (sqrt(3) x V x pf) and reports the per phase current. Use three phase with the line voltage, typically 400 volts, when a large lighting distribution board is fed as a three phase load.

Breaker loading factor0 to 1, optional

The fraction of the circuit breaker rating you will allow as continuous design current. Set 0.8 against a 16 ampere breaker and the per circuit limit becomes 12.8 amperes, capped by the max circuit load. This is what turns the circuit breaker rating from a passive comparison into the number that calculates the split, and the compliance check limit moves with it. Blank keeps the old behaviour, where max circuit load alone sets the limit.

Max points per circuitwhole number, optional

Caps the number of lighting points on one final subcircuit. The circuit count becomes the larger of the current driven figure and the points driven figure, so 40 points with a limit of 15 gives at least three circuits regardless of how low the current is. A "Points per Circuit" compliance check appears when this is set.

Emergency luminaires and watts eachcount, watts, default 3 W each

Number of emergency luminaires and the charging plus operating watts per fitting. This load is calculated separately and never enters the general lighting total or the general circuit split, because AS 2293 wants the emergency arrangement kept apart. It gets its own current and its own circuit count, and is added to the general design load only in the combined figure at the board.

Exit signs and watts eachcount, watts, default 5 W each

Same treatment as the emergency luminaire count, on a separate per unit wattage since illuminated exit signs and emergency luminaires draw different amounts.

Target densitywatts per square metre, optional

Overrides the premises type density target. Use it when a project brief or a National Construction Code Section J allowance gives you a specific number. Blank uses the premises type target.

Assumptions and limits

This is a circuit loading tool, not a lighting design tool. It tells you how much current the fittings draw and how many circuits that needs. It does not tell you whether the space will be bright enough.

What the tool assumes

• Current defaults to watts divided by volts at a power factor of 1.0. Power factor is now an input, so if you know the driver figure, enter it and the current is recalculated properly. Left at the default, the result matches the old behaviour and understates the current on cheap drivers.
• The circuit count is the design current divided by the per circuit limit, rounded up, and then raised further if a points per circuit limit binds. The load is still assumed to split perfectly evenly across those circuits, which is why the amperes per circuit figure always passes its own check. Real installations split by area or by switching zone and are rarely even, so check the worst loaded circuit yourself.
• Control gear factors are flat multipliers by type unless you set a per row factor. Neither the type factor nor the per row factor varies with wattage, driver quality or dimming.
• Every fitting is assumed to be on simultaneously at full output. The only reduction available is the Appendix C load group (a) diversity tied to the premises type, or your own override. There is no dimming allowance and no daylight or occupancy control reduction.
• The premises type diversity values and the watts per square metre targets are indicative planning figures. They have not been checked against the current published edition of AS/NZS 3000 Appendix C or against National Construction Code Section J, and they need CPEng validation before you rely on them.
• Emergency and exit load is a flat count multiplied by a per unit wattage. It models the normal operating draw at the board, not battery duration, charge profile or the AS 2293 classification.

What it does not do

Treat the output as an indicative circuit loading figure. Check it against the current edition of AS/NZS 3000 and AS 1680, and have the responsible person for the installation review and sign off the final design. Nothing here is validated or certified.

Worked examples

Four examples covering a single circuit LED office, a mixed type warehouse needing several circuits, a case where the lighting density check fails, and a hotel using the advanced options end to end. Every figure comes from the same arithmetic the calculator runs.

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.