What this calculates — Total lumens required = (E × A) / (UF × MF) for indoor rooms, or (E × A × 1.25) for outdoor. UF is interpolated from the room index k = L·W / (Hm·(L+W)) and your wall reflectance. MF defaults to 0.8 (configurable in Settings → Pricing). Fixture grid is balanced by the room's aspect ratio. Spacing is centre-to-centre between fixtures; wall margin is half-spacing (industry convention for even illumination).

Uniformity check (S/Hm) — for general-diffuser luminaires, spacing-to-mounting-height ratio should stay ≤ 1.5 for visually uniform illumination. The tool flags rooms that exceed this threshold so you can add fixtures or use a wider-beam fitting.