Light a hologram?

Hi guys,

I want to create a classic hologram effect (like the Princess Leia / R2D2 effect) BUT I only want the holograms to show up when you shine your torch at them or they stand under a street light etc.

Its like I want to feed the output of a simple lambert style shader (ie: calculate the lighting of the surface) and then feed the output of that calculation into the emissive slot of an Unlit/Additive shader (to make a totally transparent hologram).

Any tips? I’m pretty new to shader networks in UE4 so don’t be put off if the answer seems really obvious to you. I just can’t work out how to take one shader and pipe its illumination result into the emissive slot of another.

Thaks