Luminous Intensity Converter

About the luminous intensity converter

Luminous intensity describes how much visible light a point source emits in a given direction, weighted by the response of the human eye. The SI unit is the candela (cd), one of the seven SI base units, originally defined by the brightness of a standard candle. Flashlight, headlight, and stage-lighting manufacturers publish output in candela because it tells you how concentrated the beam is, unlike total flux in lumens. This tool converts candela to legacy units like candlepower and the Hefner candle that still appear in older datasheets.

Frequently asked questions

• What is the difference between candela and lumens? +

  Candela measures intensity in a single direction; lumens measure the total light output in all directions. A laser can have very low lumens but enormous candela because all the light is focused into a narrow beam.

• Is candela the same as candlepower? +

  They are very close but not identical. Modern "candlepower" is usually treated as a synonym for candela, but the older international candle equals about 0.981 cd.

• Why does a 1,000-lumen flashlight quote millions of candela? +

  Reflectors and lenses concentrate the lumens into a tight cone. Peak beam candela can be 10,000× the lumen number when the beam is narrow.