Illuminance Converter — Lux to Foot-Candle, fc to lx

Illuminance measures how much luminous flux falls on a surface per unit area — light arriving at a desk, wall, or work plane. European and SI specs use lux (lx); US lighting plans often use foot-candles (fc); older photometry texts may quote phot (ph). This converter switches between those units from one input.

One lux equals one lumen per square metre (1 lx = 1 lm/m²). Enter a value, pick From and To units, and read the result instantly. All math runs locally in your browser.

The exact relationship:

fc = lux ÷ 10.7639  ·  lux = fc × 10.7639

Quick anchors: 1 fc = 10.76 lux · 100 lux ≈ 9.29 fc · 300 lux ≈ 27.9 fc (typical office) · 500 lux ≈ 46.5 fc · 1,000 lux ≈ 92.9 fc (detailed bench work). Use this when comparing US datasheets to EN 12464 workplace tables quoted in lux.

One foot-candle is one lumen per square foot (lm/ft²). A square metre is about 10.76 times larger than a square foot, which gives the conversion factor.

The phot is a CGS unit: 1 phot = 10,000 lux = 929 fc. Practical illuminance levels (approximate): moonlight ~0.3 lux · living room ~50–150 lux · office 300–500 lux · supermarket ~750 lux · overcast daylight ~10,000 lux · full sun up to ~100,000 lux. These describe incident light on a surface — not lamp wattage.

Illuminance (lux, fc) is light arriving at a surface. Luminance (cd/m², nit) is light leaving a surface — what the eye sees as brightness of an object or screen. They are not interchangeable unit conversions.

For a diffusing reflector with reflectance ρ, a useful approximation is:

L (cd/m²) ≈ E (lux) × ρ ÷ π

Example: 500 lux on a white wall (ρ ≈ 0.8) gives L ≈ 500 × 0.8 / π ≈ 127 cd/m². This tool converts illuminance units only — not cd/m².

Illuminance on a surface is not the same as electrical watts on a lamp. They connect through lumens, efficacy, and room geometry:

• Lumens (lm) = watts × luminous efficacy (lm/W)
• Illuminance E (lux) = lumens on the work plane ÷ area (m²)

You cannot convert fc directly to watts without knowing how many lumens reach the surface and over what area. Convert fc to lux here, then use lighting design methods for a specific room.

Occupational standards specify minimum lux for tasks: corridors ~100 lx, general office 500 lx, technical drawing 750 lx, precision assembly 1,000 lx. US documents in foot-candles divide the lux target by 10.764.

Incident light meters often read in lux or fc. Converting between lx and fc keeps exposure notes consistent when switching between metric and imperial equipment manuals.

This tool converts lux, foot-candle, and phot using standard factors. It does not convert luminance (cd/m²), luminous flux (lumens) without area geometry, electrical watts, or colour temperature (K).