Lighting Design Calculator
Work out how many luminaires a room needs to reach a BS EN 12464-1 lux level by the lumen method. Enter the room, the target illuminance and the fitting, and the tool returns the luminaire count, a to-scale layout grid, the spacing, the average maintained illuminance, the power density and a printable calculation report. A first-pass design aid — for uniformity, glare (UGR) and point-by-point results, we model it in DIALux.
Every value is indicative — targets are a subset of BS EN 12464-1 and the utilisation factor is generic; verify against the standard and the luminaire's photometric data before issue.
This calculator is a first-pass lighting design aid using the lumen (average-illuminance) method. Illuminance and glare targets are an indicative subset of BS EN 12464-1; the utilisation factor is from generic distribution-class tables and the authoritative value comes from the luminaire's photometric file (use the override UF field with the manufacturer's figure). Uniformity, point illuminance and UGR glare require a point-by-point calculation. Every value must be confirmed before a design is issued — the design remains the responsibility of the engineer.
How the Lumen Method Sizes a Lighting Scheme
The lumen method is the classic way to size a general lighting scheme to an average maintained illuminance. The number of luminaires is N = E × A / (Φ × UF × MF) — the target lux E times the floor area A, divided by the luminaire output Φ, the utilisation factor UF and the maintenance factor MF. The utilisation factor depends on the room index k = (L·W) / (Hm·(L+W)) — how the room's proportions and the mounting height above the working plane, together with the ceiling, wall and floor reflectances, determine how much of the light actually reaches the working plane. This tool computes all of that, lays the fittings out on a sensible grid and checks the spacing-to-height ratio for uniformity.
BS EN 12464-1 Lux Levels
Pick the space and the calculator loads the maintained illuminance and glare (UGR) target from a built-in subset of BS EN 12464-1 — 500 lx for offices, 300 lx for circulation-heavy areas, 750 lx for fine industrial work, and so on — or type your own target. The result shows the average illuminance achieved, the power density in W/m² and the luminaire efficacy, so you can sanity-check a scheme or a manufacturer's quote in seconds. It reuses the same standards our DIALux lighting design service works to.
From a Quick Check to a Full DIALux Design
The lumen method gives you the average — it does not give uniformity (Uo), point-by-point illuminance, glare (UGR) at the observer, emergency lighting to BS 5266, or a 3D render. For that we build the room in DIALux evo with the real photometric files and produce a submission-ready pack. To get a head start, this tool can export a DIALux STF file (beta) — open it in DIALux evo with Import STF… to rebuild the room and luminaire grid, then finish the photometric calculation there. Need the distribution side too? Size the final circuits with our BS 7671 cable sizing calculator. When you need the full lighting design done and checked, see our DIALux lighting design service.