By Zencalcy Editorial TeamLast reviewed About us
Luminous flux is the total visible light emitted into a region, measured in lumens. It equals the luminous intensity multiplied by the solid angle the emission covers, so a uniform source radiating in all directions sends 4π times its candela value into the sphere.
Flux from intensity and solid angle.
Φ = I Ω
Φ is luminous flux in lumens, I luminous intensity in candela and Ω the solid angle in steradians. A full sphere subtends 4π sr.
| Symbol | Meaning |
|---|---|
| Φ | Luminous flux, in lumens. |
| I | Luminous intensity, in candela. |
| Ω | Solid angle, in steradians. |
Φ = 100 × π = 314.2 lm. The same source radiating uniformly over a full sphere would emit 1,257 lm.
Continue with the Magnification Calculator, Magnifying Glass Calculator, or the Malus's Law Calculator — or browse more optics and light tools and all physics calculators.
4π, about 12.57. A hemisphere is 2π and a narrow cone can be much less than one steradian.
Results are computed from the standard equations of classical mechanics. Unit conversions use the SI definitions published by NIST. Air resistance is ignored unless the calculator names a drag model.
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Content updated: September 2026