Lighting Design Calculator

Calculate the number of light fixtures needed using the lumen method: N = (E × A) / (F × UF × MF).

Target Illuminance

lux

IES Handbook: corridors 100 lux; warehouse 100–200 lux; office 300–500 lux; labs 750–1,000 lux

Room Area

sq ft

Lumens per Fixture

Utilization Factor (UF)

Maintenance Factor (MF)

Mounting Height

Tab to move between fields

Fixtures Needed

21 fixtures

Actual Illuminance

504 lux

Total Lumens105,000 lm

Lighting Power Density0.98 W/ft²

How to Use This Calculator

Enter the Target Illuminance in lux: office work ≈ 500 lux, warehouse ≈ 200 lux, precision tasks/labs ≈ 750–1000 lux.
Enter the Room Area in m² and the mounting height above the work plane in meters.
Enter the Lumens per Fixture from the manufacturer's datasheet (initial lumens, not depreciated).
Set the Utilization Factor (0.4–0.7) based on room shape and surface reflectances — use the fixture's photometric data for accuracy.
Set the Maintenance Factor (0.6–0.8): clean environments ≈ 0.8, dusty or industrial ≈ 0.6.
Read the number of Fixtures Needed and the Actual Illuminance — adjust fixture layout to achieve target lux while staying within energy code limits (Lighting Power Density in W/ft²).

How the result changes with Lumens per Fixture

Target Illuminance: Required maintained illuminance per IES RP-1 (office), IES RP-7 (industrial), and ASHRAE 90.1. IES recommended values: office task 300–500 lux; conference 300 lux; warehouse 100–200 lux; labs/precision 750–1000 lux; corridors 100 lux.
Room Area: Total floor area of the room to be lit.
Lumens per Fixture: Initial lumen output of each light fixture. Check manufacturer data.
Utilization Factor (UF): Fraction of lumens reaching the work plane. Depends on room shape and surface reflectances. Typical: 0.4-0.7.
Maintenance Factor (MF): Light loss factor for dirt and lamp aging. Clean environment = 0.8, dirty = 0.6.
Mounting Height: Height of fixtures above the work plane (affects spacing and uniformity).

Identify Input Parameters
4 parameters
Target Illuminance = 500, Room Area = 100, Lumens per Fixture = 5000, Utilization Factor (UF) = 0.6 = 6 input(s) provided
Calculate Fixtures Needed
Fixtures Needed = max(fixturesNeeded
21 = 21
Calculate Actual Illuminance
Actual Illuminance
504 = 504
Calculate Total Lumens
Total Lumens
105000 = 105000
Calculate Lighting Power Density
Lighting Power Density
0.98 = 0.98