For the lighting I'm using a mix of ray tracing and stochastic cone tracing. Cone tracing mainly because it's very cache friendly and almost doesn't introduce any noise.
I'm not really using a regular cellular automata or rules, it's just similar on the aspect that the simulation is based on neighbors.
I took some inspiration from Noita and Sandspiel, but I found that falling sand simulations aren't flexible enough and I was thinking about how a system could be created to visually program the behaviour of circuits or stuff like falling sand yourself.
Also Noita is single buffered, while my simulation is double buffered which actually makes a huge difference in the possible features you can realize. Single buffering is faster but much more chaotic and "random", while with double buffering you get very precise behaviour. Also the simulation was designed from the ground up to be run on the GPU, while Noita and Sandspiel are CPU-based. Here's [0] a video of a previous 2D prototype doing falling sand on the GPU
Can you please describe the cellular automata rules you're using, what your goals and techniques were, and what inspired you?