Lighting & rendering · Advanced

Caustics

Bright patterns of light focused by glass, water or polished metal

What are caustics in rendering?

Caustics are the bright patterns of light that form when a curved glass, water or polished metal surface focuses light onto a nearby area. Think of the wobbly lines on the floor of a swimming pool. In 3D, they are one of the hardest lighting effects to render cleanly.

Think of it like this

It is like using a magnifying glass to gather sunlight into a bright spot, only spread into rippling lines and curves.

Where it fits in a 3D project

  1. Create
  2. Surface
  3. Rig
  4. Animate
  5. Render
  6. Export

Render: Lighting the scene and turning it into images or video.

How caustics work

  1. 01Light hits a curved clear or mirror-like surface.
  2. 02The surface bends or reflects many rays toward the same small area.
  3. 03Where those rays meet, the light concentrates into bright lines or spots.
  4. 04The renderer must find those focused paths, which takes many samples.

Where caustics are used

  • Light through a glass of water or wine
  • Rippling patterns under pools and shallow sea
  • Jewelry and perfume bottle renders

Beginner tip

Caustics often cause fireflies. If you do not need them, turn them off in the render settings; if you do, use a larger light and plenty of samples.

Terms related to caustics

Caustics FAQ

What causes caustics?
Curved surfaces that bend or reflect light, such as water, glass or polished metal. They redirect many rays toward the same spot, and that concentration shows up as bright patterns.
Why are caustics hard to render?
A path tracer usually starts its rays at the camera, and only rarely does a random path pass through the glass and land exactly on a light. With so few successful paths, caustics come out noisy or speckled.
Can you render caustics in Blender?
Yes, with its path-tracing engine. Recent versions add shadow caustics options that mark which objects cast and receive them, which cuts the noise. Real-time engines usually fake caustics with a moving texture.

Updated October 29, 2026 · Browse all 3D terms