Attenuation of a light source:

Without attenuation, the light has the same intensity on all points, whatever the distance with the light source.

The attenuation can be linear or quadratic. The quadratic attenuation gives a faster decrease of the light intensity.

The attenuation is set by two parameters:

the intensity distance - distance where the intensity is equal to its initial value,

the half-intensity distance - distance where the intensity is equal to the half of its initial value.

For mathematical reasons, the half intensity distance can not be less than twice the reference linear distance, and 1.4 times in quadratic mode.

When values are entered in the distance fields, the full and half intensity spheres appear in the graphic area. Then you can select them and drag their limits in the graphic area.

Attenuation example: