This category of measurement units is defined by the "luminous intensity" type, which is an SI base quantity.
The SI base unit for luminous intensity is the candela.
The candela (symbol: cd) is the SI base unit of luminous intensity. It is the power emitted by a light source in a particular direction, weighted by the luminosity function. A common candle emits light with a luminous intensity of roughly one candela. The candela is officially defined as the luminous intensity of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity of 1/683 watt per steradian.