[jimminy]

What I am trying to do is create a material that can be mapped to a ceiling that will essentially stay white, even when very little or no light is hitting it, that doesn't emit any light.

The purpose is to simulate interior ceiling mounted lights in external renders of buildings, usually high-rises, so that those "lights" can be seen through the exterior glass even when there is a lot of reflectivity in the glass. It would be acceptable that nothing of the interior is visible besides these lights.

There is very little light actually hitting the surface so using a map with white for the lights doesn't work, not enough light hits it, and if I use emitters I will have hundreds and it will be very slow to render and to set up, not to mention doing nothing to improve the render since I don't want the interiors illuminated.

thanks!

[brodie_geers]

So you can't use a non-emitter or an emitter. That's a tricky one.

What about doing it post process. You could turn off your glass material, run a MatID and select the ID that matches the color of your "lights" and then maybe a color fill with some glow on a blended layer or something?

-Brodie

[jimminy]

Yeah, that's interesting and not too complicated. Wouldn't that mean 2 renders, one with glass on and one without? Not a big deal if so, just wondering.

Best case scenario is that there's no post work though.

[brodie_geers]

Yes, 2 renders, however, for the one with the MatID, you wouldn't have to run any other channels besides the MatID so it would be very quick.

-Brodie

[jimminy]

Was just trying the material ID thing, and I'm wondering how (or if it's even possible) to get the different color values in a single map to take on different MatID values.

[brodie_geers]

if you want to select individually, it's probably better to use the object id instead.

-brodie

[jojojoj]

why not applying a render tag and check "hide from GI" ? works here....

[jimminy]

Success!! Thanks jojojo, that works. I didn't really understand what you meant by applying a render tag, but I just selected the objects with the map that had the "lights" I want to show through the glass, checked the hidden from: Global Illumination box and it works just as I wanted.

Thanks again!

[jfrancis]

Sounds like you have a solution but I was going to suggest one poly slammed through multiple rooms with lights texture-mapped onto them or clip mapped so that it's one poly appearing as many correctly shaped lights.

Would that work? Or would the emitter poly / wall intersections make things slow?

[eric nixon]

jfrancis your right, low poly emitter plane with tiled map of ceiling lights and corresponding alpha, is the best way, you DO have to avoid intersecting walls, but this way you wont need the render tag, because it renders pretty quick.