So… I’m not sure if you guys are open to feature requests but a while back I had an idea for a fake window light in order to address the issue of small windows causing noisy/splotchy lighting in interiors. Basically it’s just a rect or spot light whose color is set by sampling the skylight texture in the general direction the window is facing. Since it samples the skylight texture, the lighting color is dynamic. Lights Intensity is scaled by an artist control.
Anyway here’s a sample of the results:
Video of it adjusting in realtime (after I press simulate it begins to use the fake window light):
Another example in a real scene:
As you can see there are some noticeable benefits to this:
- Significantly improved soft shadow detail provided by VSM/MDF shadowing
- Improved hit lighting reflections by providing more hit lighting
- Reduced splotchiness and noise, especially on high scalability.
- Dynamically updates, provides plausible lighting even in sunset conditions
A spotlight could be chosen instead of a rect light depending on the desired performance characteristics, and it otherwise has access to all the same controls as a regular light.
As noted I am using the skylight texture, I wonder if this could be improved by getting the color from Lumens translucent lighting volume from a point a bit behind the light? This would allow the light to take into account things like skylight shadowing and exterior bounce light which my implementation doesn’t do. Might even be useful for stationary lightmaps as an alternative to lightmass portals (which incur huge build time costs).
I think this would provide a higher cost, but higher quality alternative to skylight leaking or albedo boosting, since both of those create a mismatch between the screen and the surface cache which is an issue this method doesn’t suffer from.
Anyway… I’m not a tech artist, the way I had to implement this is awful (I can elaborate on it if needed) so I think people who knew what the hell they’re actually doing could be much better. I don’t know how feasible (or desirable) any of this really is to implement but I think it could be useful and I hope you’ll consider adding it 
Huge thanks to whoever was responsible for exposing the SkyLight texture to the material editor… honestly something I’ve wanted for a long time.