What is the law of illumination?

Inverse square law, also known as the first law of illumination, is that when a point light source is used for illumination, the illuminance of the object surface perpendicular to the light source is directly proportional to the luminous intensity of the light source, and inversely proportional to the square of the distance from the illuminated surface to the light source.

The intensity of light is determined by two factors: (1) the luminous intensity of the light source; (2) The distance between the illuminated object and the light source. Under the condition of artificial light, the illuminance is inversely proportional to the square of the distance from the light source, that is:

E=I/R2

E is light; R is the distance from the object to the light source; I is the luminous intensity of the light source.

Inverse square law works like this: If you double the distance between the main body and the light source, it will illuminate a surface area four times larger than before. Therefore, we usually multiply the distance itself by the distance to calculate the increase of surface area. However, a larger surface area results in the light intensity being inversely proportional to the square of the distance-because the same amount of light must be distributed over a larger surface area.

Extended data

The second law of illumination: when an object is illuminated by parallel light, the illumination on the surface of the object is directly proportional to the cosine of the incident angle of the light.

For parallel light, the illumination law can be expressed by the following formula:

E = E0？ cosθ

Where θ is the included angle between the surface normal and the light (unit); E is the illuminance of the surface when light comes from the θ direction (unit LX); E0 is the illuminance of the surface when the light is parallel to the normal of the surface (unit lx).

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