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Lux to Lumens & Candela Distance Calculator

Calculate illuminance (lux / foot-candles), beam pool diameter, and required lumens at any distance using the optical Inverse Square Law and beam angle photometrics.

Practical Lighting Presets

Calculation Mode

UNITS

Meters (m)Feet (ft)

Luminous Flux (Lumens)800 lm

50 lm800 lm3,000 lm10,000 lm

Beam Angle (FWHM)40°

10° (Narrow Spot)40° (Flood)120° (Diffuse)

Distance to Surface1.50 m (4.9 ft)

0.2 m2.5 m5.0 m10.0 m

Derived Beam Intensity:2,084 cd

Surface Illuminance

926 lx

86.0 fc

Beam Pool Diameter

1.09 m

3.58 ft

Effective Coverage Area

0.94 m²

10.1 sq ft

Solid Angle (Steradians)

0.38 sr

Cone Steradians

Dynamic Beam Cone Visualizer

Simulates the luminous cone projection and geometric spread on the target plane.

40° Beam

Photometric Laws & Physics Formulas

Understanding the mathematical relationship between luminous flux (lumens), luminous intensity (candela), solid angle (steradians), and illuminance (lux) is fundamental to architectural lighting design.

1. INVERSE SQUARE LAW

E = I / d²

Illuminance drops dramatically with distance. If you double the distance from a spotlight to a desk, illuminance on the surface is divided by four (2² = 4).

2. CONICAL SOLID ANGLE

Ω = 2π × (1 - cos(θ/2))

A narrow 20° spot confines lumens into only 0.095 steradians, concentrating intensity to high candela. A wide 120° panel spreads lumens across 3.14 steradians.

3. BEAM POOL DIAMETER

D = 2 × d × tan(θ / 2)

Calculates the 50% cutoff light circle on the floor or worktop. Use this formula to properly space recessed downlights without scalloping or harsh overlapping shadows.