Lightmass settings for mirror-like materials


I have a mirror-like material in my scene (base color = white, metallic = 1, specular = 0.95, roughness = 0) used on static actors, which I would like to reflect a lot of light when I build static lightning for the level.

I have tried to set e.g. Diffuse Boost to 100 under Lightmass Settings for this material, but that doesn’t affect how much light it reflects when building light for the level (at least, I don’t see any change).

Where do I change how much light a material reflects for static lightning?

Thanks a lot in advance for all help.

Kind regards,
Uffe Flarup

That type of effect is actually caustics, which isn’t supported by Lightmass

I’m guessing I can fake the effect using some additional static light sources near the reflective objects, and carefully tweak the amount of light they emit. Any other suggestions for workarounds?

You could set metallic to 0 for Lightmass with LightmassReplace node.

Thanks for the advice. I’ll play around with this and see if I can get the desired effect.

Just tested that my self and it seems that lightmass is already doing that.

The effect I want to achieve is the following:

I have a wall with a glass-window, and both are directly hit by sunlight. There’s another wall not too far from them (which is NOT directly hit by sunlight), and I want this wall to be hit by reflected light from the other wall (this part works, as the shaded wall clearly receives some reflected light).

But, I would ALSO love to have the window reflect “more” light onto the shaded wall, such that the shape of the window is clearly visible on the shaded wall, since the glass-window reflects more light than the brick wall it’s in.

Is such an effect possible to achieve when baking light using lightmass?

Thanks a lot in advance.

Could you give any reference photo from real world. Glass isn’t actually very reflective so I am not sure that I follow what you are meaning.

If i’m understanding you correctly your best bet would be to use an emissive, half opaque decal to fake it.

Couldn’t you also shine a spotlight through the window from the other side? You’d have to work out the exact angle the light would be reflecting at, but it would work I think. It would also depend on if you need to see the outside of that wall.

The effect I want to achieve was right outside our office window this afternoon :slight_smile: It’s the reflections of the windows on the wall on the other side of the street which I want to have. You can see the pictures here:

If it’s possible to make something similar using Lightmass, then I would love to do this, so it simply get baked in with the other lightning. But so far I’ve been unable to make a material for the window which reflects light (for Lightmass baking) this way.

I’m sure that I can get the effect using another light behind the window, or by using a decal - and these things would definitely be the next things to try. But it would just be less work during level design if it automatically would be baked into the lightmaps using Lightmass.

Is it possible to obtain this effect from a window material using Lightmass?

Thanks a lot in advance.

Kind regards,
Uffe Flarup

Just what i thought you were trying to achieve and no, not possible with lightmass. Two of your options to fake it; light function(with additional movable light sources) or decals.

Thanks a lot for the clarification. I’ll experiment with additional light sources or decals.

Ironically, Lightmass uses photon mapping to calculate indirect lighting, but it doesn’t support caustics…