Caustic (optics)

When light shines on an object, sometimes it makes the object look different. This is called a caustic. Think about how a shadow looks different when the sun is shining through a stained glass window. The light is bending and bouncing off the glass in a certain way that creates a cool pattern on the ground.

In optics, caustic effects are caused by something called refraction. That means when light passes through a certain material, like water or glass, it can bend in different ways. When you put a straw in a glass of water, it looks like it's bent. That's because the light is bending as it goes from the air in the straw to the water in the glass.

Now imagine shining a light onto a reflective object with a curved surface, like a spoon. The light will reflect off the spoon and bounce around in different directions. If you have a white wall nearby, the caustic effect might make a pattern on the wall that looks like little rainbows. This is because the curved surface of the spoon is bending the light in a certain way, creating the cool pattern on the wall.

So basically, a caustic effect is when light bends and bounces in a certain way, making an object or surface look different. It's mostly caused by refraction in materials like water or glass, or by reflecting off curved surfaces.