invisible material that reflects light bounces as normal - Need help ASAP

[lersince1991]

Hi,

I'm trying to do a lighting study of a model looking in from the outside as a perspective section. I want one of the sides to be invisible but still allow rays to bounce off it in order to not distort the results from my study. How can I make the side like this?

I have attached an example of the model I am using and showing the only light source from above.
I have deleted the side walls in photoshop but the front wall is non existent. how can I make the front wall affect the light bounces inside but make it invisible?

I've now made it an emissive material with 0 intensity and made it invisible to the eye. do emissive materials reflect ray bounces or not?

Need help ASAP please, i.e. tonight if possible please!
Thanks!
Luke