UE5 Path Tracing Viewport Mode vs PPV

Hello all,

I’m trying to create an accurate simulation of mirror reflections in UE5. I did some digging and determined that I need to focus on global (indirect) illumination Light Transport Algorithms, the first example of this that I found was path tracing, and I’m currently trying to modify my project to use it. From what I understand, path tracing is one way to implement global illumination, and UE5’s Lumen GI uses a different algorithm.

I want to see the light spot produced by bouncing direct light off of a mirror, I learned that most game engine LTAs don’t carry this functionality, as it is very computationally demanding. Meaning in order to get path tracing to work, I need to mess around with some settings.

In UE5 you can actually get a Path Tracing viewport mode, this mode gives me the effect that I want. In this image, the mirror itself is visible on the surface, but so is the light spot it makes, and they blend together slightly due to noise.

(Light spot is on upper right hand corner of the surface)

I’ve tried setting up a global PPV that only uses Path Tracing for its lighting and here’s the result:

(Mirror is reflected, but no light spot)

Here are my path tracing settings in the PPV, all forms of global illumination are turned off:

→ So really, I’m wondering what the difference is between my PPV configuration and what Unreal does when I enter path tracing view. I’m hoping to have the same effect occur in the regular lit view with my PPV as when I enter path tracing mode. Are there any noticeable discrepancies in my PPV settings, or things I’m not considering?

→ Notes: I have hardware raytracing and path tracing enabled in my project settings, I run this project on a 1660 Ti.