Candela to Lumen Converter

About this calculator

Candela (cd) measures luminous intensity — how much light a source throws in one specific direction — while lumens (lm) measure luminous flux, the total light output spread across the beam. The two are related through the solid angle the beam covers: Φv = Iv · Ω, where for a cone-shaped beam with apex (full) angle θ the solid angle in steradians is Ω = 2π(1 − cos(θ/2)).

Manufacturers often publish a spotlight or LED fixture’s candela rating and beam angle on the datasheet rather than its total lumen output, since candela describes brightness along the beam axis (what matters for throw distance) while lumens describe overall output (what matters for illuminating an area). Lighting designers use this conversion to compare fixtures on a common basis or to estimate the total flux of a narrow spotlight versus a wide floodlight. This calculator takes your candela value and beam apex angle and returns the equivalent luminous flux in lumens.