How to change Sun Light "Shape"

I am trying to change the shape of my Sun Light with a script but I don't know how I can do it.
It's a smart property:

I first tried to modify it like this:

print(propSunLight:SetSmartProperty("Shape","Cheese Moon Sliver"))

But that doesn't work. I also tried to set the shape as an integer. But it looks like I didn't write the correct name for the property.

So I tried to find it with the debugger:
And as you can see, it can't be found in smart properties.

What can I do?