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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1 Watt equals 683 Lumens of light power at wavelength 555 nm. At other wavelengths 1 Watt is less Lumens as it takes into account the sensitivity of the average human eye.
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At exactly , radiant intensity corresponds to luminous intensity . This convention specifies a direction, rather than the source's total luminous flux. [ref]
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.