SI base unit: candela (cd)
The candela, symbol cd, is the SI unit of luminous intensity in a given direction. It is defined by taking the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency
This definition implies the exact relation Kcd =
![](/documents/20126/42149531/SI-equation-cd-1.jpg/a0f689e8-278d-8db2-2656-ef3587d613d4?t=1594243185663)
which is equal to
![](/documents/20126/42149531/SI-equation-cd-2-EN.jpg/35ddaf55-4e3d-8600-fa63-30baec162640?t=1594243651417)
The effect of this definition is that one candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency
See:
SI Brochure - Appendix 2
SI Brochure - excerpts from Appendix 4