 Candela

Candela is Lumen density per solid angle. A sphere emitting 1 Candela uniformly in all directions produces 4π Lumen total power.

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Candela is a unit of measurement for luminous intensity in the International System of Units (SI). It quantifies the amount of light emitted by a source in a specific direction. One candela is defined as the luminous intensity of a source that emits monochromatic radiation of frequency 540 × 10^12 Hz and has a radiant intensity of 1/683 watt per steradian. In practical terms, the candela helps in comparing the brightness of different light sources.