Commercial Lighting Demand Calculator

A commercial lighting demand calculator converts entered lighting connected load into an adjusted lighting load in volt-amperes (VA) and the resulting line current in amperes. The calculated current is used during preliminary branch-circuit, feeder, panelboard, and lighting-system load review.

Lighting load is often entered from fixture schedules, lighting-control documentation, tenant improvement plans, or connected driver and ballast nameplate data. The worksheet applies the entered Demand factor (%) and Continuous multiplier (%) to each lighting row before converting the adjusted VA total to current at the selected system voltage and phase model.

The result supports practical design work such as:

• Reviewing preliminary feeder and panel loading
• Estimating lighting current for a 480 V three-phase distribution system
• Comparing lighting demand against available switchboard or panel capacity
• Establishing a starting current value for conductor ampacity review
• Supporting raceway routing, conductor-count planning, and voltage-drop evaluation

The calculator reports electrical load arithmetic. Conductor size, AWG or kcmil selection, insulation temperature rating, terminal rating, adjustment factor, correction factor, current-carrying conductor count, raceway fill, overcurrent protection, and final installation approval remain separate field and code decisions.

Related lighting and load tools: Commercial Load Calculator, Continuous Load Calculator, and Feeder Load Calculator.

Worksheet Inputs

Each Lighting load rows entry represents a distinct lighting load group. A row may correspond to a lighting panel section, fixture type, floor area, tenant space, exterior lighting group, or other useful load-scheduling category.

Interface field	Electrical purpose
Load label	Identifies the lighting load group for schedule review and calculation traceability.
Connected load (VA)	The installed lighting load before the entered demand and continuous-load treatment.
Demand factor (%)	The percentage of the connected load carried forward as demand load for that row.
Continuous multiplier (%)	The percentage multiplier applied to the row’s demand load to produce its continuous adder. A value of 125 applies a 1.25 multiplier.
System voltage (V)	The voltage used to convert the final adjusted VA total into line current.
Phase model	Selects the line-current conversion. The displayed phase multiplier changes with the selected model.

The worksheet begins with one row, Row 1, and allows additional rows through Add row. Remove deletes a row. The Load row count result records the number of active lighting load rows included in the calculation.

Demand and Continuous Load Arithmetic

For every lighting load row, the calculator first determines the demand load:

\(\displaystyle \text{Demand Load} = \text{Connected Load} \times \frac{\text{Demand Factor}}{100}\)

It then calculates the continuous adder from the row’s demand load:

\(\displaystyle \text{Continuous Adder} = \text{Demand Load} \times \left(\frac{\text{Continuous Multiplier}}{100} - 1\right)\)

The row adjusted load is the demand load plus its continuous adder:

\(\displaystyle \text{Adjusted Load} = \text{Demand Load} + \text{Continuous Adder}\)

Equivalently:

\(\displaystyle \text{Adjusted Load} = \text{Connected Load} \times \frac{\text{Demand Factor}}{100} \times \frac{\text{Continuous Multiplier}}{100}\)

The worksheet totals all entered rows and displays:

• Connected load — Sum of all entered Connected load (VA) values.
• Demand load — Sum after each row receives its Demand factor (%).
• Continuous adder — Additional VA created by the Continuous multiplier (%) above 100%.
• Adjusted load — Final VA total used for current conversion.
• Line current — Calculated current at the selected System voltage (V) and Phase model.
• Phase multiplier — The divisor used in the phase-specific line-current conversion.

A 100% Continuous multiplier produces no continuous adder. A 125% Continuous multiplier increases the demand load by 25%, so a 10,000 VA demand load produces a 2,500 VA continuous adder and a 12,500 VA adjusted load.

Three-Phase Line Current

For the selected Three-phase model, the calculator displays a Phase multiplier of 1.7321, which is the numerical value of sqrt{3}. The line-current result is calculated as:

\(\displaystyle \text{Line Current} = \frac{\text{Adjusted Load}}{ \text{System Voltage} \times 1.7321}\)

For a 480 V three-phase lighting load:

\(\displaystyle \text{Line Current} = \frac{\text{Adjusted Load}}{ 480 \times 1.7321}\)

The calculated current represents the three-phase line current associated with the entered adjusted lighting VA. It is not a conductor-size selection. A feeder or branch-circuit design still requires verification of actual circuit arrangement, conductor ampacity, terminal limitations, equipment ratings, voltage drop, and installed conditions.

Calculation Example

Assume a commercial lighting schedule contains two load groups supplied from a 480 V three-phase system.

Load label	Connected load (VA)	Demand factor (%)	Continuous multiplier (%)
Office lighting	24,000	100	125
Exterior lighting	6,000	100	125

The worksheet processes each row separately.

Office lighting

\(\displaystyle 24{,}000 \times 1.00 = 24{,}000\text{ VA Demand Load}\)

\(\displaystyle 24{,}000 \times (1.25 - 1.00) = 6{,}000\text{ VA Continuous Adder}\)

\(\displaystyle 24{,}000 + 6{,}000 = 30{,}000\text{ VA Adjusted Load}\)

\(\displaystyle 6{,}000 \times 1.00 = 6{,}000\text{ VA Demand Load}\)

\(\displaystyle 6{,}000 \times (1.25 - 1.00) = 1{,}500\text{ VA Continuous Adder}\)

\(\displaystyle 6{,}000 + 1{,}500 = 7{,}500\text{ VA Adjusted Load}\)

\(\displaystyle \text{Connected load} = 24{,}000 + 6{,}000 = 30{,}000\text{ VA}\)

\(\displaystyle \text{Demand load} = 30{,}000\text{ VA}\)

\(\displaystyle \text{Continuous adder} = 6{,}000 + 1{,}500 = 7{,}500\text{ VA}\)

\(\displaystyle \text{Adjusted load} = 30{,}000 + 7{,}500 = \text{37,500 VA}\)

\(\displaystyle \text{Line current} = \frac{37{,}500}{480 \times 1.7321} = 45.1\text{ A}\)

The worksheet result is therefore 37,500 VA adjusted load and approximately 45.1 A line current at 480 V three-phase. That current can be carried into a preliminary feeder load schedule or used as an input for a separate conductor ampacity and voltage-drop review.

Field Verification

The worksheet applies only the entered Demand factor (%) and Continuous multiplier (%). It does not determine whether a lighting load qualifies for a particular demand treatment, whether a continuous-load multiplier is required, or which value applies to a specific occupancy, lighting system, or installation.

Verify the following separately before finalizing a commercial lighting circuit or feeder:

• Actual connected lighting VA from approved fixture, driver, ballast, and lighting-control information.
• Circuit voltage and phase configuration at the equipment actually supplying the lighting load.
• Whether loads are distributed and balanced as assumed across the three-phase system.
• Branch-circuit and feeder conductor ampacity using the applicable conductor material, AWG or kcmil size, insulation temperature rating, terminal rating, correction factor, and adjustment factor.
• Current-carrying conductor counts and raceway fill where shared conduits contain lighting, controls, or other conductors.
• Voltage-drop performance for long lighting feeders, exterior lighting runs, and remote tenant spaces.
• Available panelboard, switchboard, transformer, generator, or service capacity.
• Applicable code requirements and the final interpretation of the AHJ.

The calculator’s stated planning boundary is limited to the mode worksheet: it does not perform occupancy-table analysis, feeder selection, service sizing, or authority determination.