Grim, as we all know PS lighting effects filter works only on one layer at a time which makes changes a big pain. But jstuartj has a good idea. 50% grey is a neutral colour so creating a layer and changing the "blend mode" to OVERLAY will let you apply the lighting effect to the whole composition (as long as you place it at the top).

If you find you need to change the intensity (decrease) of the lighting effect you just need to change the opacity of the layer. If you find you need to change it only in certain areas of your composition, you can add a "layer mask" and paint a mask with grey where you want less light. If you need to boost the light more (increase), duplicate the layer and adjust the opacity to fit your needs.

As for being able to move, rotate, change directions... who's to say you can't try the "free transform" tool on the grey layer and see...

let us know if this is of any help (or if we're WAY off base ;) )

:)
retrocity