Luminous intensity (candela) is the light emitted into a particular direction, measured per unit solid angle. Divide the lumens by the solid angle in steradians.
What the terms mean
| Symbol | Meaning |
|---|---|
| I | Luminous intensity, in candela |
| Φ | Luminous flux, in lumens |
| Ω | Solid angle, in steradians (sr) |
Worked example
1,000 lumens concentrated into a 2 sr cone gives 500 candela.
See the Inverse Square Law and Candela Distribution Calculator.
Luminous intensity (candela)
Luminous intensity, measured in candela (cd), is the light emitted in a particular direction per unit solid angle (the steradian). In plain terms it captures how concentrated a beam is, independent of distance — which is why it’s the basis for comparing spotlights. For a source radiating evenly into a cone, intensity ≈ lumens ÷ solid angle, and a narrower cone packs the same lumens into fewer steradians, raising the candela.
Candela links directly to illuminance through the inverse-square law: lux = candela ÷ distance². That’s what makes intensity so useful — once you know a fixture’s candela toward a target, you can predict the lux landing on it at any distance. High candela means punch and reach; total lumens still tells you overall output.