Lighting Design Calculator
Design a lighting layout with fixture count, wattage, and spacing recommendations based on room type and dimensions.
Results
Visualization
How It Works
Lighting design uses the Lumen Method to calculate how many fixtures are needed. It accounts for room size, ceiling height (via Room Cavity Ratio), surface reflectances (via Coefficient of Utilization), and lamp depreciation (Light Loss Factor). Higher ceilings and darker surfaces absorb more light, requiring more fixtures.
The Formula
Required Lumens = (Target FC x Area) / (CU x LLF)
Fixtures = Required Lumens / Lumens Per Fixture
Max Spacing = Ceiling Height / 2
Fixtures = Required Lumens / Lumens Per Fixture
Max Spacing = Ceiling Height / 2
Variables
- FC — Foot-candles -- lumens per square foot of illumination on the work surface
- CU — Coefficient of Utilization -- percentage of emitted light that reaches the work surface (0.45-0.70)
- LLF — Light Loss Factor -- accounts for lamp aging and dirt accumulation (typically 0.85)
- RCR — Room Cavity Ratio -- describes the room proportions for CU lookup
Example
A 15 x 12 ft kitchen with 9 ft ceilings using 1,600 lumen fixtures: Target = 50 FC. Area = 180 sqft. CU = 0.60, LLF = 0.85. Lumens = (50 x 180) / (0.60 x 0.85) = 17,647. Fixtures = 17,647 / 1,600 = 12 fixtures.
Tips
- Spacing should not exceed half the ceiling height for even light distribution with recessed cans.
- Place fixtures at half the spacing distance from walls to avoid dark edges.
- Use higher lumen fixtures (2000+) for workshops and lower lumen (800-1200) for bedrooms.
- Layer with task lighting -- the lumen method calculates ambient light; add under-cabinet or desk lamps for task areas.
- Dimmable LED fixtures let you adjust light levels for different activities without redesigning the layout.