Shadow Only Light

[retroactivecontinuity]

I'm looking specifically to create a "shadow only" light used for cheating shadows with Arnold in Maya 2018.

In other programs, I can make spotlight, for instance, completely black and then assign a negative number to the value of the color shadow, and it makes the light effectively shine no light and only darken the area where the shadow would have been. Unfortunately I can't figure out how to do this in Arnold, Maya 2018 is not accepting a negative number for the value in the HSV color of the shadow.

[Stephen.Blair · Accepted solution]

You cannot have a negative intensity or color for Arnold lights.

Light links and shadow links could be the way to go.

[retroactivecontinuity]

This does not answer the question for me, or at least what I'm trying to understand to do in the program. I don't necessarily need to use a negative light, I'm not attached to that. the real question is,

Let's say I have an object and the background plane behind it perfectly lit, but I dislike the shadow the object casts on the plane behind it for cosmetic reasons. How do I cast a shadow of just that object with just one light without also lighting the background?

As far as light-linking, this can't work by definition. If I choose the object to not be linked to the light casting the shadow, so that it's previous lighting is not affected by the new light addition, then it also won't cast a shadow in the shape of the object on the background plane. So that's the first question, how does something cast a shadow without being lit itself?

The second question is how does something receive a shadow without being lit itself? So in the cast of the wall, is it only possible to add a shadow by adding more light? I understand that this is the physical definition of a shadow (i.e. there is no such thing as a shadow just lower level of light), but again, the negative light cheated that by just sucking out light in the shape of the shadow. While nothing like that exists in real life, mathematically it is easy to produce.

[retroactivecontinuity]

Also in Maya's Arnold there is no shadow link, only cast shadows or not for every light.. you can't turn it off for specific lights.

[retroactivecontinuity]

One solution to the first question I just tested is duplicating the object, turning off visibility, and simply recreating the background plane lighting with the new duplicate object linked to it and all the other lights unlinked to it.

So for instance, disable the background plane from receiving any of the lights with light-linking, create a new light that only links to the background plane, get the object's shadow and lighting right, then disable the visibility of that object, so that it is no longer there but still casts the shadow of the shadow casting lights.

However, this does mean re-creating the background plane lighting or that basically there is no way to keep lighting exactly as is while also adding a cast shadow onto the object there way there was with a negative light.