Curve opacity

Using opacity on curves can be slow to render, in this case use a fast opacity mode : Set the Surface > Opacity Mode attribute to UV or Vertex.

User Guide/Shading/Opacity for the details.

Curves and global illumination

When rendering the curves with GI, consider the following optimizations :

  1. Use the minimal Curves > Diffuse/Specular > Depth possible.
  2. Reduce the Curves > Diffuse/Specular > Ray Length attribute.
  3. Remove the curve objects from the Diffuse and the Reflection set.