someone asked me about this and I don't know how to answer them. I will attach a couple pictures. They asked me why the light penetrates a certain depth then just disappears instead of gradually fading away. Particularly in the sand bed as seen in the pictures. I've read through this https://en.m.wikipedia.org/wiki/Penetration_depth already. So is it just a property of em waves to diminish quickly depending on the medium? I just took an optic class last semester where I was fortunate enough to learn close to nothing so sorry if it's a dumb question.