Interesting... Problem with deferred rendering was twofold: 1, apparently the deferred renderer doesn't honor ambient lights, and 2, it doesn't honor THREE.DoubleSided either, and my ground plane just happened to be facing down.

It does, however, seem to honor emissive lighting, so I think I'm just going to use that for now.
Back to where we were with WebGLDeferredRenderer, except sprites don't work yet.