Light measurement units

摘要

The situation with light is just as bad as with magnetism, since there are many units in common use. The most important units are described below. Luminous flux: Used to compare different forms of lighting. The unit is lumen (Im). The luminous flux indicates the amount of light radiated per unit time. With bright green light (550 nm), a radiated power of 1 W corresponds to 683 Im. Luminous intensity: Mainly used in connection with small LEDs in the milliwatt range for signaling purposes, etc. The unit is candela (cd). Radiation with a luminous flux of 1 Im per steradian (1 sr is the solid angle of an area of 1 m~2 on the surface of a sphere with a radius of 1 m) corresponds to a luminous intensity of 1 cd.