Do you ever notice that lights in After Effects have an Adjustment Layer switch? This switch forces the light to ONLY effect 3D layers below the light in the timeline. Why would you do this?

First, it's pretty handy to use to light one specific object, like a title. But most commonly, I use this when using Light Emitters in Particular. When you use a Light for an emitter, the Light will effect all your 3D layers.  Solution: make it an Adjustment Light and put it an the bottom of your timeline.