Standard movable lights vs Light Propagation Volumes (Dynamic GI)

I’m little confused with differences between standard movable lights (directional + sky light) and Dynamic GI (Light Propagation Volumes). What are the differences and why Dynamic GI is hard to implement (because it’s not done yet) when movable lights are done.

Thanks for explanation. :slight_smile:


GI is where the light will bounce off surfaces onto other surfaces, it’s what makes lighting look realistic. If you have a room with a window and a standard light with dynamic shadows, when the light comes through the window it will only illuminate what it hits directly. In real life, the light would bounce and the whole room would have some degree of illumination.
Lightmass in UE4 can do that, but it’s static, the light can’t move. And it takes a while to calculate. That can be very limiting because if something moves, you can’t use lightmass to render nice GI. Dynamic GI is difficult to impliment because it needs to run fast, so it can’t be as good of quality as what lightmass can do, but they’re working on finding ways to do it at a lower quality that can run in real-time.
LPV is one of the dynamic GI methods, but it has a lot of limitations, mainly the quality is just too poor and it covers too small of an area.