No worries, couple of ways you can approach it to solve your design problem.
I am not sure how you do photomode, seems you are making another scene capture.
Simply you can do Capture->HiddenComponents.Add(MeshComp);
set you capture to RenderPrimitives this have option to hide components
However as a side note, think about if you really really need a render target every frame, it is a very costly thing to capture scene, you can maybe use a normal camera and upon action “take picture” you render frame once with the hidden actor of detector from scene capture (or you can even destroy light detector one frame before take snapshot)
Happy developing.