Candela (cd) is the unit of measurement for luminous intensity, for the light energy emitted by a light source in a specific direction. By definition, it is the energy emitted by a black body with 1/60 cm2 surface area at the melting temperature of platinum, at 1,770 °C during one second.
A light source has one candela when the illuminance at a distance of one meter is 1 lux( lx). The unit candela belongs to the basic units of the system of units( SI). The higher the candela value, the brighter the emitted light. One candela is divided into 1,000 millicandela (mcd). If you relate the luminous intensity to a unit area, you get the luminance, given in candela per square meter (cd/m2) or in nit. There is a relationship between luminous intensity and luminous fl ux via the solid angle in Steradian. According to this, candela results from the ratio of lumens to solid angle.
Typical candela values are between 3 and 12 candela in the living room, between 10 and 20 candela in the office, and between 60 and 300 candela for shop window lighting.
In addition to the unit candela defined in the metric system, there is also the unit footcandle used in Anglo-Saxon countries. It defines the illuminance that illuminates the inner surface of an imaginary sphere with a radius of 1 foot when the light source of one candela is located in the center of the sphere.