Illumination Converter

Convert illuminance between lux and foot-candles, the units used to measure how much light actually falls on a surface.

Illuminance Measures Light Arriving at a Surface, the Final Link in the Lighting Chain

Illuminance measures how much light actually falls on a given surface, the practical, real-world endpoint of the entire lighting chain that starts with a source’s luminous intensity, travels outward, and finally lands on the surface being illuminated, whether that’s a desk, a road surface, or a garden path. The lux, the SI unit, is specifically defined as one lumen of light flux spread across one square metre of surface, meaning illuminance depends both on how much light a source produces and, critically, on the distance and angle between that source and the surface being measured, since the same light source produces dramatically lower illuminance on a surface positioned further away or angled obliquely rather than facing the source directly, following an inverse-square relationship with distance that makes moving a light source even a modest distance closer or further away change illuminance far more than intuition might initially suggest. This is precisely the quantity referenced in outdoor and architectural lighting standards, where a target lux level on a walkway or task surface, not simply a fixture’s total output rating, is what a lighting designer is genuinely trying to achieve, since a powerful fixture positioned poorly can deliver less usable illuminance on the actual surface that matters than a modest fixture positioned well.