Corner reflectors retroreflect light, producing reflected rays that travel back in the direction from which the incident rays came.
To further increase the speed of rendering, the renderer may calculate the position of the reflected ray at each vertex.
This results in the "reflected ray" which is then passed to the cube map to get the texel which provides the radiance value used in the lighting calculation.
The two reflected rays now travel in the same direction to be detected.
For mirrors with parabolic surfaces, parallel rays incident on the mirror produce reflected rays that converge at a common focus.
In other words, if a circle reflected parallel rays of light, the reflected rays would envelope a nephroid.
Therefore, the reflected rays of a radiation spectrum incident on a real surface in a specified direction forms an irregular shape that is not easily predictable.
