Lighting Layout Calculator Formula
Understand the math behind the lighting layout calculator. Each variable explained with a worked example.
Formulas Used
Fixtures Needed
fixtures_needed = lumens_per_fixture > 0 && cu_factor > 0 && maint_factor > 0 ? ceil(total_lumens_needed / (lumens_per_fixture * cu_factor * maint_factor)) : 0Total Lumens Required
total_lumens = total_lumens_neededEstimated Wattage (LED)
watts_estimate = lumens_per_fixture > 0 && cu_factor > 0 && maint_factor > 0 ? ceil(total_lumens_needed / (lumens_per_fixture * cu_factor * maint_factor)) * lumens_per_fixture / 100 : 0Variables
| Variable | Description | Default |
|---|---|---|
room_length | Room Length(ft) | 20 |
room_width | Room Width(ft) | 15 |
target_fc | Target Foot-Candles(fc) | 50 |
lumens_per_fixture | Lumens per Fixture(lm) | 3200 |
cu_factor | Coefficient of Utilization | 0.6 |
maint_factor | Maintenance Factor | 0.8 |
room_area | Derived value= room_length * room_width | calculated |
total_lumens_needed | Derived value= room_area * target_fc | calculated |
How It Works
Lumen Method for Lighting Design
N = (Area x FC) / (Lumens per Fixture x CU x MF)
Where FC is the target foot-candle level, CU is the coefficient of utilization (depends on room shape and reflectance), and MF is the maintenance factor (accounts for dirt and lamp aging).
Worked Example
20x15 ft office at 50 fc using 3,200-lumen fixtures, CU=0.6, MF=0.8.
room_length = 20room_width = 15target_fc = 50lumens_per_fixture = 3200cu_factor = 0.6maint_factor = 0.8
- 01Area = 20 x 15 = 300 sq ft
- 02Lumens needed = 300 x 50 = 15,000 lm
- 03Effective per fixture = 3200 x 0.6 x 0.8 = 1,536 lm
- 04Fixtures = 15,000 / 1,536 = 9.77, round up to 10
Ready to run the numbers?
Open Lighting Layout Calculator