Why doesn't shadows have an umbra and penumbra?

[eobet]

I just discovered these not very realistic shadows when I used the built-in lighting environment:

[DriesV]

My guess is that the light source in the HDRI is very small with little scattering.
The penumbra will only be noticeable for larger, more diffuse lights. E.g. On overcast days, shadows will be more diffuse.

In KeyShot 7, the 'Sun Size' parameter in Sun & Sky allows to quickly adjust the "softness" of shadows from the sun. Larger Sun Sizes will yield softer shadows.

Dries

[eobet]

Ok, but regardless, shadows do not behave that way. The further from the surface receiving the shadow the casting object is, the blurrier it should be...

Having a shadow evenly sharp or evenly blurry is something I've only seen in games so far, not 3D rendering programs.

[Esben Oxholm]

Ok, but regardless, shadows do not behave that way. The further from the surface receiving the shadow the casting object is, the blurrier it should be...

I think that if the light source has an infinite small radius, then the shadow will be equally sharp no matter how far it is from the object.
I agree that it might be unrealistic as a default for the sun&sky system, but changing the sun size to something in the range of 20-50 should soften up your shadow.

Cheers,