What is the difference between candela and lumens?

Candela (cd) measures light intensity in a specific direction (lumens per steradian), while lumens (lm) measure total light output in all directions. A 1000 lumen bulb might be 80 cd with a wide 120° beam or 2000+ cd with a narrow 15° spot beam. Candela tells you how bright light appears when looking at it; lumens tell you total light produced.

How do I convert candela to lumens?

Use the formula: Lumens = Candela × Solid Angle (steradians). For beam patterns, solid angle = 2π(1 - cos(θ/2)) where θ is beam angle. For a 30° spot: Ω ≈ 0.21 sr, so 1000 cd × 0.21 = 214 lumens. For a full sphere (isotropic): Ω = 4π ≈ 12.57 sr, so 1000 cd = 12,566 lumens.

What is a steradian and solid angle?

A steradian (sr) is a unit of solid angle - the 3D equivalent of radians. A full sphere contains 4π (≈12.57) steradians. A hemisphere is 2π sr. A typical spotlight with 30° beam angle covers about 0.21 sr. Solid angle determines how spread out light is, connecting candela (intensity) to lumens (total output).

How do I choose between narrow and wide beam angles?

Narrow beams (10-25°) concentrate light for accent lighting, spotlights, and task areas - high candela from fewer lumens. Wide beams (60-120°) spread light for general illumination - lower candela from same lumens. Match beam to use: narrow for artwork/products, medium (25-40°) for general spotlights, wide for ambient fill lighting.

What candela values are typical for common light sources?

LED indicators: 0.001-0.1 cd. Candle flame: 1 cd. 60W incandescent: 65-80 cd average. Car headlight (low beam): 2,500-10,000 cd. LED spot (35W): 5,000-15,000 cd. Stadium floodlight: 100,000+ cd. Lighthouse: 1,000,000+ cd. Higher candela means more intensity in the viewing direction.

Why does the same lumen bulb have different candela ratings?

Beam angle concentrates or spreads the same total light. A 1000 lumen LED at 15° beam produces ~5,500 cd peak intensity. The same 1000 lumens at 120° beam produces only ~100 cd. Narrow beams appear brighter at center but illuminate smaller areas. Choose based on whether you need intensity (narrow) or coverage (wide).

Candela to Lumen Converter

Convert between candela (luminous intensity) and lumens (luminous flux) based on solid angle and beam pattern. Calculate light output for spotlights, LEDs, and isotropic sources.

CIE StandardsIES Handbook

Input Parameters

Enter luminous intensity or flux value and select the radiation pattern