Luminaire Quantity Estimator
Estimate a starting fixture count for indoor general lighting using the lumen method. Enter project-specific assumptions before using the result.
Calculation inputs and results
Enable JavaScript to use the estimator. Fixture count = maintained illuminance (lx) × area (m²) ÷ (luminaire output in lm × room utilance × maintenance factor), rounded up to a whole fixture.
A count estimate does not establish spacing, uniformity, glare, emergency-lighting compliance or hazardous-area suitability. Check the final layout with IES/LDT photometry. Mounting height and surface reflectance must be reflected in the selected utilance; beam footprint alone cannot determine fixture count.
Quantity calculation method & limits
N = ceil(E × A ÷ (Φ × U × MF)). E is maintained average illuminance in lux; A is area in m²; Φ is initial complete-luminaire output in lumens. After rounding up, estimated maintained average = N × Φ × U × MF ÷ A. Connected load = N × input watts.
The IES lumen method estimates average illuminance. Room utilance here is based on luminaire output; lamp-based coefficient of utilization uses a different flux denominator. Keep the factor and lumen basis consistent. The maintenance factor accounts for reduction relative to initial illuminance.
This simplified model is for preliminary indoor general-lighting estimates over one open area. Obstructions, local task lighting, unusual geometry and nonuniform layouts require a photometric model. Utilance depends on the layout, so check it again after selecting the fixture count.
The illustrative example uses 500 m², 300 lx, 20,000 lm, U = 0.60 and MF = 0.80: 15.625 rounds up to 16 luminaires, giving an estimated 307.2 lx. At 150 W each, connected load is 2,400 W. These are demonstration inputs, not recommended targets or TORMIN product data.
Supported ranges: area 0.000001–1,000,000 m²; each dimension 0.000001–1,000,000 m; target 0.000001–1,000,000 lx; output 1–1,000,000,000 lm; input power 0–1,000,000 W; U and MF 0.01–1. Counts above 1,000,000 are outside this tool’s range. Unit conversion uses 1 ft = 0.3048 m and 1 fc = 1 / 0.3048² lx.