Luminous Intensity converter

Luminous intensity is anchored to the candela (cd), one of the seven SI base units, describing light emitted in a particular direction. Millicandela and kilocandela simply scale that by a thousand in each direction, and lumen per steradian is not a different measurement at all — it is the literal definition of the candela, so its factor is exactly 1.

The featured pair is candela to millicandela: mcd = cd × 1,000, with the reverse direction multiplying by 0.001.

A bright panel-mount indicator LED rated at 20 cd converts to 20 × 1,000 = 20,000 mcd, the scale its datasheet almost certainly uses instead. In the other direction, a tiny SMD status LED rated at 50 mcd converts to 50 × 0.001 = 0.05 cd.

Luminous intensity in candela is how beacons, lighthouses, vehicle headlamps and signal lights, and handheld flashlights are all officially rated, since it captures brightness in the specific direction that matters for those applications. Small indicator and status LEDs, by contrast, are almost always specified in millicandela because their actual output in candela would be an inconveniently small decimal.

The most useful thing to know for interpreting older or marketing literature is that candlepower, Hefner candle, and the carcel unit are retired historical "candle" standards from different national traditions (British, German, and French respectively), each built around a specific reference flame or lamp that burned slightly brighter or dimmer than the modern candela — which is exactly why their conversion factors (0.981, 0.903, and 9.61) are not round numbers. "Candlepower" in particular still turns up informally in flashlight and automotive-lighting marketing today, even though it has not been a defined scientific unit for a long time, so a quoted candlepower figure should be treated as approximate rather than as a precise candela value.