Light source intensity:

Allows you to modulate the light intensity. The point light and the spot can have an unspecified intensity. The ambient light and the directional light can have intensity between 0 and 1.

The intensity represents the coefficient to multiply the RGB color values of the lighted element.

An intensity of 1 does not modify the color.

An intensity of 0.5 divides by half the RGB values.

An intensity of 2 doubles the RGB values (in the limits of 255).

The intensity modification is only interesting if combined with the attenuation, because of the 255 limitation.