Lumens to Candela Converter

About This Tool

This tool converts luminous flux (lumens, lm) to luminous intensity (candela, cd) using standard photometric relationships. It is designed for lighting engineers, product specification teams, energy analysts, and facility managers who need direction-specific brightness calculations or quick fixture comparisons. By providing a simple numeric interface, it supports fast validation of light-source specs, enables consistent documentation in datasheets, and facilitates engineering reviews without the need for manual calculations.
Conceptually, lumens measure total light emitted by a source, while candela measures light emitted per unit solid angle. For an ideal isotropic source over the full sphere, Φ = I × 4π, so I = Φ ÷ 4π. The tool implements this default and also accepts a user-specified solid angle Ω (in steradians) for non-isotropic distributions, using the general relation I = Φ ÷ Ω. When Ω is provided, the conversion directly reflects angular emission, and you can compute the total lumen output from a candela value with Φ = I × Ω.
Core features include: lumen input (required), optional input solid angle Ω (sr) with a default of 4π sr, output candela (cd) with numeric formatting suitable for engineering data, and validation. If lumens = 0, output is 0 cd. If Ω ≤ 0, the computation is invalid and flagged. The tool supports quick checks by changing Ω to reflect different radiation patterns, and it documents results suitable for specification sheets and energy simulations.
Use cases span fixture specification, photometric data verification, comparative analysis between candidate sources, and compliance documentation. Industry standards rely on SI units; all inputs/outputs use lm, cd, and sr. The tool does not model spectral response, luminance, or perceived brightness beyond the geometric relation between flux and intensity. Assumptions include SI-conforming inputs and explicit default isotropic behavior to minimize user error.

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