Attempting both faux and accurate simulation of light shining through thin translucent white plastic

Hey all.

I have been using three.js to flesh out a tool to help with the placement of LEDs on circuit boards for a light box. I am running into issues on finding any example of what I am trying to achieve.

Ideally I am wanting two rendering modes. The more complex one which I know can be done uses
a path tracing rendering library that has many properties to be able to do multiple passes where it computes the light bouncing through a transmissive material. I hope I can blend the colour fall off of multiple light source this way. I have found this and plan to implement it one day, however I am more focused on the below

The other mode is a much simpler mode where I think I can translate the light that falls onto one side of a plane (or box), onto the opposing side. The reason this mode needs to exist is that I would like a smooth rendering experience when nudging the light sources around during runtime. The accurate mode takes a long long time and only should be run afterwards.

The light technically doesnt shine through the material, it just remaps the result. I am not knowledgeable around shaders or materials, but my guess is that it needs to either flip some vertices directions on one of the maps of a StandardMaterial, or that the light needs to be baked in someway at runtime?

I would like to prove that I can get one of these two concepts working first before I start fleshing out the rest of the features as it would be waste if Three.js is not able to do this.

I would very much appreciate any project direction advice as I have no shader code experience and have been scrolling through examples for days.

Thankyou very much.