9f7dbe57__units___UK_Metric_Association_SI_base_units_it_measures_and_its_definition
[Unit name] candela [Symbol] cd
Luminous intensity Essentially, this measures the 'brightness' of radiation. It is defined in terms of the intensity of a very pure yellow-green light source with a strength measured by its power spread over a cone shaped beam. Luminous intensity, in a given direction, of a source that emits monochromatic radiation at a frequency of 540 x 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.
Base units | UK Metric Association
What it measures and its definition