In Blender, I think we also use area lights a lot that simulate light originating from a surface. The area light produces shadows with soft borders by sampling a light along a grid the size of which is defined by the user.

https://docs.blender.org/manual/en/latest/render/lights/light_object.html

Why is this r^2?

^I think the square makes sense if you interpret light coming from the point source as kind of a sphere that grows outward. As the light travels outward, it's evenly distributed over the surface of that sphere, whose surface area grows with the square of the radius.

Is there anything in between? Say the cone of the light?

Nvm. Saw the slides later. :)

Wondering what other light sources approximate an infinitely far away light. I used Blender's sunlight simulation in my CS148 project, it was pretty impressive and had an angle parameter. See https://www.youtube.com/watch?v=RgJGm-iT5cY.