News

Light intensity calculation method of point light source

In lighting engineering, it is often necessary to calculate the illuminance generated by a known light source on a surface. The simplest example is the illuminance generated by a theoretical "point light source" with equal light intensity in all directions on a plane. In practice, it refers to the situation where the size of the light source is very small compared to the distance from the light source to the surface. Light source S emits luminous flux in all directions and illuminates plane P. The luminous flux ðΦ intercepted by the element area ðA on plane P is the luminous flux emitted within the solid angle ðω formed by the element area ðA to the light source, assuming that there is no absorption of light between the light source and the surface. ðΦ/ðω is called the luminous intensity I in a specific direction; that is

I=ðΦ/ðω (1.10)

The unit of luminous intensity is lumen/steradian (lm/Sr), or "candela" (cd). Therefore, luminous intensity is the luminous flux emitted per steradian in a specific direction. Radiant intensity can also be defined as radiant flux per steradian.

Generally speaking, luminous intensity varies with the direction of the emitted light. If the luminous intensity is equal in all directions, the light source is called a uniform light source. The total luminous flux emitted by a uniform point source with a light intensity of one candela is 4π lumens.

PREVIOUS：Illuminance - the concept and unit of lightin NEXT：The structure of the human eye