Ljusenhet

Ljusenhet is a historical non-SI unit of luminous intensity used in Sweden and other Scandinavian regions. The term combines ljus, meaning light, with enhet, meaning unit, and it was used in older technical and everyday texts to describe how bright a light source appeared.

Historically, the ljusenhet was tied to the brightness of a standard candle. However, the exact definition varied over time and between jurisdictions, because candles used for such standards differed in composition (for example, tallow or spermaceti) and size. As a result, the value attributed to one ljusenhet was not uniform, and regional standards often diverged.

With the standardization of lighting measures and the adoption of the International System of Units, the ljusenhet fell out of use as a precise unit. In many historical sources it is treated as roughly equivalent to one candela, but this equivalence is approximate and not reliable for precise measurement. Modern literature usually references candela, lumen, and lux for luminous intensity, luminous flux, and illuminance, respectively.

Today, the term ljusenhet is primarily of interest to historians of science, lighting researchers studying historical texts, and collectors of antique lighting equipment. It serves as a linguistic and historical reminder of how lighting was quantified before standardized SI units became common practice.