Ok this might sound silly (to me anyway) but have you try checking if you didn't accidentally disable the environment map? You already mentioned isolating the spray alone but as far as I know, Texture Environment cannot be isolate unless you disable it manually.

If you are using the Texture ...

IF you need a precise selection of the light sources as a separate pass, the Emitters pass from the Render Elements is handy too as it only render any object that cast light in the scene.

I use it a lot when I composite in Nuke as it allows me to track in a lens flare with the Emitters pass and ...

Just upgraded mine and can't wait to try out the new features later.

Kudos to everyone at OTOY.