I just found a workaround to something and thought I'd post it here in case it turned out to be something that helps someone else (since I've received so much help on these forums in the past).
I needed a light to shine on a logo in a scene set up in 3D space, but didn't want it to affect any other layers so I set it up as an Adjustment Light. However, it still was affecting the layers below the logo of course, and putting just the light and logo in a precomp for some reason didn't work. The light didn't seem to work at all that way, not even on the logo it was intended for. Putting my light and logo at the bottom of the layers wasn't an option either for various reasons.
So after trying a few different things, I tried placing the Adjustment Light layer above my logo, set at 100% intensity. Then I duplicated the light and placed the copied light right underneath my logo and set that light's intensity to -100%, effectively canceling out that light's affect on all the layers below the logo.
I remembered using negative lights in Maya a while back before I found out about Light Linking. So I've used the same principle in AE as there is no Light Linking in After Effects that I know of- using negative light to subtract light from certain areas of complex 3D scenes, based on where in the scene the negative light is placed.
But what I hadn't thought of was that the same principle can be applied with Adjustment Lights, but that negative lights can be controlled not only by where they are placed in a scene, but as an Adjustment Light, a negative light also be controlled in a different way by where it is placed in the layer order which seems to make things much easier (so far). I've only used it in 2 projects so far but both times it's worked the way I needed it to.