Luminositetsenhet

Luminositetsenhet, the Norwegian term for the unit of luminous intensity, refers to the SI base unit candela (cd). Luminous intensity measures the power emitted by a light source in a particular direction, weighted by the relative sensitivity of the human eye to wavelength. One candela is defined as the luminous intensity in a given direction of a source that emits monochromatic radiation of frequency 540×10^12 Hz (corresponding to green light) with a spectral flux density of 1/683 watt per steradian. The factor 1/683 W sr⁻¹ ensures that the candela is connected to the photometric unit lumen, which represents perceived brightness.

The candela is one of the seven base SI units and is used throughout photometry, lighting engineering, and display technology. In practical applications, luminous intensity is measured with photometers or integrating spheres, and is expressed in candela or millicandela for very low intensities. Common devices are rated in candela, for example, a typical LED may emit 20 cd, while a high‑intensity discharge lamp could produce thousands of candela. Luminous intensity is distinct from luminous flux (lumen) and illuminance (lux), the latter being the flux received per unit area. Understanding the candela is essential for designing lighting systems that satisfy visual comfort, safety, and energy‑efficiency standards.