Light attenuation modes issues

I’m having a hard time understanding how Blender light attenuation works, reading that:
http://wiki.blender.org/index.php/Doc:2.6/Manual/Lighting/Lights/Light_Attenuation

First of all, this paragraph confuses me big time:Zeroing both “Linear” and “Quad”

If both the Linear and Quadratic sliders have 0.0 as their values, the light intensity will not attenuate with distance. This does not mean that the light will not get darker, it will, but only because the energy the light has is spread out over a wider and wider distance. The total amount of energy in the spread out light will remain the same though. Light angle also affects the amount of light you see. It is in fact the behavior of light in the deep space vacuum.

This makes no sense to me. AFAIK, all that attenuation mechanics exists to emulate the physics of light. The paragraph says that even if Linear=0 and Quad=0 there is something else out there that attenuates the light :spin:. Meanwhile, the graphic shows that the light intensity is constant for this case (see “d” curve), contrary to what is being said…

Secondly, my test scene shows that the light is actually computed somewhat differently from what is being described:


The experiment is done as follows. I set the light distance to be approximately the actual distance to the surface (see the screenshot). According to the theory (described in the URL provided), the light distance is where the intensity gets half of the original. This means to me that an expected intensity for the scene should be roughly the same between Inverse Linear and Inverse Square, the graphic shows that where the curves “a” and “b” intersect at (20,0.5) coordinates. In practice, the scene gets significantly darker (like 2x or 3x, even blind could see the difference) when I switch from Inverse Linear to Inverse Square.

Please tell me if there is any explanation of that :confused:. I’m on Blender-2.62 OSX release. And thank you for reading this.

They mention “…The total amount of energy in the spread out light will remain the same though.”
That means it is not attenuated. Just spread out over larger distance.