The candela (abbreviation, cd) is the Standard International (SI) unit of luminous intensity. Like other SI base units, the candela has an operational definition—it is defined by a description of a physical process that will produce one candela of luminous intensity.
Since the 16th General Conference on Weights and Measures (CGPM) in 1979, the candela has been defined. that is, power emitted by a light source in a particular direction, weighted by the luminosity function (a standardized model of the sensitivity of the human eye to different wavelengths, also known as the luminous efficiency function). A common candle emits light with a luminous intensity of roughly one candela. If emission in some directions is blocked by an opaque barrier, the emission would still be approximately one candela in the directions that are not obscured.
So A candela is a measurement of the intensity of light, used in the SI measurement system. In the modern age, it is technically defined as the intensity in a given direction of a source that emits monochromatic radiation of a frequency of 540 x 10^12 hertz and which has a radiant intensity in the same direction of 1/683 watts per steradian.
||SI photometry units|