Candela ↔ Lumens Conversion Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 10/11/2026
Total luminous flux (lumens) is calculated from luminous intensity (candela) and the beam's solid angle: lumens = candela × Ω, where Ω = 2π × (1 − cos(angle/2)). For a 1000 cd flashlight with a 30° beam, the total flux is about 214 lumens.
Explanation
Candela and lumens measure two different aspects of light emitted by a directional source like a flashlight or spotlight: candela (cd) measures luminous intensity in a specific direction (typically the beam's central axis, where light is most concentrated), while lumens (lm) measure total luminous flux, i.e. all the light emitted across the whole beam. These two quantities are only related once you know the beam angle: the same intensity in candela, concentrated into a narrow beam, gives a lower total flux in lumens than a wide beam, because the light is spread over a smaller solid angle. This solid angle, expressed in steradians (sr, the SI unit of solid angle), is calculated from the full beam angle (in degrees, as given on the product's spec sheet) via Ω = 2π × (1 − cos(angle/2)): this formula gives the area cut out by the cone of light on a sphere of radius 1, expressed per steradian. This distinction explains why two flashlights advertising the same candela intensity can have very different total luminous fluxes if their beams differ in width — and why some manufacturers market candela (which favors a narrow, powerful beam, useful for lighting far away) rather than lumens (which favors a high total flux, useful for lighting a wide nearby area). For the illuminance received at a given distance rather than the intensity or flux emitted, see our illuminance conversion calculator.
Example: a 1000 cd flashlight, 30° beam
Inputs
Luminous intensity: 1000 cd. Beam angle: 30°.
Calculation
Solid angle = 2π × (1 − cos(15°)) = 2π × (1 − 0.9659) ≈ 0.2143 sr. Luminous flux = 1000 × 0.2143 ≈ 214.1 lm.
Result
This flashlight emits a total luminous flux of about 214 lumens, concentrated into a narrow 30° beam.
Frequently asked questions
Why don't two flashlights with the same candela intensity have the same lumen output?
Because total luminous flux also depends on the beam angle: a flashlight that concentrates its light into a narrow beam (say, 10°) reaches a high candela intensity with a relatively modest total lumen output, while a flashlight that spreads the same intensity over a wide beam (say, 90°) produces a much higher total flux, since the light is emitted over a much larger solid angle.
Should I prioritize candela or lumens when choosing a flashlight?
It depends on the use case: candela (and the resulting throw distance) matter more for lighting far away precisely (search, signaling), while lumens matter more for lighting a wide nearby area (camping, DIY work). A flashlight optimized for throw (high candela, narrow beam) won't necessarily light up a whole room better than one with high lumens and a wide beam.
Where do I find my flashlight or spotlight's beam angle?
It's usually given on the product's spec sheet or packaging, sometimes labeled "beam angle" or "dispersion angle." Absent a precise figure, a typical flashlight beam often falls between 15° and 30°, and a wide domestic lighting spot between 60° and 120° — see our room lighting power calculator to estimate the total flux needed based on the room's use.