Does anyone know if there is a way that I can use the glow channel to glow only when its in a shadow? In other words if I light an object so that half of its in a shadow and half of its in the light, the only part that glows is the half that is in the shadow. Is that a possibility? If anyone knows how, please let me know. Thanks.

Maybe you could use a glow map on it after you determine where the shadow falls. Would be tedious to apply to animation, obviously - but one frame wouldn't be too difficult.

That's the problem it is for an animation. I know that 3DS has a falloff map that you can set to self-illuminate in the dark but not in the light. Does Carrara have that option?

If the glow isn't too bright, it will be washed out in the light areas, but still show in the shadows. For example, if you use a 50% value of the color in the glow channel, the light at 100% should overpower it...

that's a good tip, but when I do that I don't get the desired glow strength in the shadows.

How about a mask in the animation? Layer 2 is the animation with glow. Then Layer 1 (above layer 2) is the animation without the glow, and you mask out everything but the part of the object in the light. Assuming you have a video editor that does layers and masks, like QT Pro or many others.

I'll try that, I was hoping to avoid doing a double render and compositing but if I have to then I have to. Thanks for the help.

Attached Link: Extending possibilities

On the Yahoo Carrara group something like this was discussed (city lights on the dark side of earth), and some solution was found using the extension Shader Ops by Digital Carvers Guild, worth checking out!

Thanks for the info, but I already own shader ops.

Then search for the thread in groups. You have to use UV shifter or something (it was about light interacting with the shader in an animation, so rather on-topic). I do not have Shade Ops so I don't understand it, actually.