Lighting Load Calculator

A lighting load calculator converts an area-based lighting allowance into volt-amperes (VA) and then into the current used for preliminary branch-circuit, feeder, panelboard, and service load review. The final output is Lighting current, which provides the electrical load value needed to evaluate conductor ampacity, overcurrent protection, available panel capacity, raceway planning, and voltage-drop exposure.

The calculation starts with the project’s floor area and Lighting load density in VA per square foot. It applies the selected Demand factor, then applies the Continuous multiplier. The resulting adjusted VA is converted to amperes at the stated System voltage using either single-phase or balanced three-phase current math.

Lighting Load Basis

The calculator uses these inputs:

Input	Electrical purpose
Area	Floor area or project area assigned to the lighting load block, in square feet
Lighting load density	Lighting VA basis in VA/sq ft
Demand factor	Percentage applied to connected lighting load
Continuous multiplier	Percentage applied after the demand factor
System voltage	Nominal voltage used to convert adjusted VA to current
Phase	Selects single-phase or balanced three-phase current calculation

The Lighting load density is the connected-load basis. It is not an actual measured wattage reading from installed luminaires unless the project basis has been established that way. The value should match the load basis used for the particular project, design calculation, or load-review workflow.

A demand factor reduces or preserves the connected VA before the continuous multiplier is applied. With a Demand factor of 100%, the calculator carries the full connected lighting load forward without reduction.

Load and Current Formula

The calculation sequence is:

\(\displaystyle \text{Connected lighting load} = \text{Area} \times \text{Lighting load density}\)

\(\displaystyle \text{Demand lighting load} = \text{Connected lighting load} \times \left(\frac{\text{Demand factor}}{100}\right)\)

\(\displaystyle \text{Adjusted lighting load} = \text{Demand lighting load} \times \left(\frac{\text{Continuous multiplier}}{100}\right)\)

For the selected phase arrangement, the calculator converts adjusted VA to current:

\(\displaystyle \text{Single-phase lighting current} = \frac{\text{Adjusted lighting load}}{\text{System voltage}}\)

\(\displaystyle \text{Balanced three-phase lighting current} = \frac{\text{Adjusted lighting load}} {\sqrt{3} \times \text{System voltage}}\)

The calculator reports four values:

• Connected lighting load — area multiplied by the lighting load density.
• Demand lighting load — connected lighting load after the demand factor.
• Adjusted lighting load — demand lighting load after the continuous multiplier.
• Lighting current — current corresponding to adjusted lighting load at the selected voltage and phase.

Calculation Example

Using the stated values:

Input	Value
Area	2,500 sq ft
Lighting load density	1.3 VA/sq ft
Demand factor	100%
Continuous multiplier	125%
System voltage	277 V
Phase	Single-phase

Connected Lighting Load

\(\displaystyle 2{,}500\ \text{sq ft} \times 1.3\ \text{VA/sq ft} = 3{,}250\ \text{VA}\)

Connected lighting load = 3,250 VA

Demand Lighting Load

\(\displaystyle 3{,}250\ \text{VA} \times 1.00 = 3{,}250\ \text{VA}\)

Demand lighting load = 3,250 VA

Adjusted Lighting Load

\(\displaystyle 3{,}250\ \text{VA} \times 1.25 = 4{,}062.5\ \text{VA}\)

Adjusted lighting load = 4,062.5 VA

Lighting Current

For 277 V single-phase current math:

\(\displaystyle \frac{4{,}062.5\ \text{VA}}{277\ \text{V}} = 14.6661\ \text{A}\)

Lighting current = 14.6661 A

This 14.6661 A value is the load current to carry into the next design or estimating step. For example, it can be compared with branch-circuit or feeder ampacity, combined with other calculated loads in a panel schedule, or used as the load value for a voltage-drop calculation.

Use in Circuit and Feeder Review

Lighting current is not selected in isolation. A lighting circuit may share a panelboard, feeder, raceway, or service with receptacle, HVAC, motor, and equipment loads. The adjusted lighting load should be added to the applicable load calculation before selecting feeder conductors, service equipment, or distribution capacity.

For a branch circuit or feeder review, the calculated current may affect:

• Conductor size in AWG or kcmil.
• Overcurrent protective device selection.
• Panelboard bus and breaker loading.
• Feeder ampacity.
• Raceway fill when additional conductors are installed.
• Voltage-drop calculations for long circuit runs.
• The count of current-carrying conductors used in conductor adjustment-factor review.
• Available capacity when lighting loads are added to an existing distribution system.

The current result does not itself establish a conductor size. Conductor selection also depends on termination conditions, insulation temperature rating, ambient temperature, bundled or grouped conductors, applicable correction factor and adjustment factor, equipment ratings, and the installation’s approved design basis.

Field and Code Limits

The calculator performs the stated VA and current arithmetic from the entered values. It does not determine whether the entered Lighting load density, Demand factor, or Continuous multiplier is appropriate for a particular occupancy, jurisdiction, design method, or AHJ requirement.

Verify separately:

• The actual area assigned to the lighting load block.
• The correct system voltage and whether the load is properly treated as single-phase or balanced three-phase.
• Whether the lighting load is continuous under the governing installation requirements.
• Actual connected luminaire, driver, ballast, and control-equipment characteristics where those values govern the project calculation.
• Branch-circuit and feeder conductor ampacity after applicable ambient-temperature correction and current-carrying-conductor adjustment.
• Terminal rating limits, overcurrent protection, voltage drop, raceway fill, and panel capacity.
• Final code compliance with the adopted electrical code, project specifications, equipment instructions, and AHJ interpretation.

Related calculations: LED Driver Load Calculator, Lighting Layout Calculator, Lumen Calculator.