candela
SI base unit for luminous intensity (symbol: Math - text). The Math - text is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency Math - ei and that has a radiant intensity in that direction of (Math - ei) Math - text per Math - text.
Source:
Green Book, p. 70
PAC, 1996, 68, 957 (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 964