1) Go to or create a dark area, or use night time environment setting

2) Create a prim, turn it into a light.

3) Set light radius to a value, for example 3

4) in Build -> Options enable show light radius for selected light

5) Select your light

6) Observe that the light illuminates area past the debug light sphere

In the attached image the box has size of 1x1x1, with radius of 4, the light sphere appears to match in size, yet the ceiling is illuminated past the sphere volume.

Expectation: there should be no light outside the sphere.

Use Case: I was setting up lights in my house, and I was making sure the radius stayed within the room, so the light would not bleed into the room upstairs. However, I still saw objects upstairs illuminated from below. While the debug sphere was below the floor, the light effect extends past it, making it more difficult to precisely place lights.