How would I grab the lighting pass in a post process shader for deferred lighting?

Guess it's all in the title.

I want to run the output of the lighting pass (in deferred rendering) through a look up table, this sounds simple if I can just grab the lighting pass in a post process shader. How would I go about doing that?

I've seen 'Grab pass' wondering if that'll do what I want but I have no idea how to work out the name of the lighting pass to us within that. http://docs.unity3d.com/Manual/SL-GrabPass.html

=== edit: Ok I've found the command buffer, that seems like it'll do what I want, having a little trouble as the command buffer is very poorly documented and no examples given :\

so far I know I want to use 'CameraEvent.AfterLighting' and then render the resulting texture with a shader that uses a look up table... just need to work out how