You can render raytraced shadows with software-render type particles.

To create raytraced shadows with particles

1. Create your particles and set the Render Type to Cloud, Blobby, or Tube.
2. Add a directional, point, spot, or area light to the scene.
3. Display the Attribute Editor for the light and display the Shadows Attributes.
4. Turn on Use Ray Trace Shadows (under Raytrace Shadow Attributes).
5. In the Render Settings window, display the Raytracing Quality attributes and turn on Raytracing.
6. Do one of the following:
   • If you want particles raytraced in a mirror, display the particle Attribute Editor and turn on Visible in Reflections (under Render Stats).
   • If you want particles refracted in glass, turn on Visible in Refractions (under Render Stats).
     NoteMake sure Casts Shadows is turned on (under Render Stats). It is on by default.
     TipIf you get strange looking or missing shadows when rendering cloud or tube particles with raytraced shadows, it may be that the Ray Depth Limit is too low. Increase the Ray Depth Limit for the light that is using the raytraced shadows by an increment of 1 per software-rendered particle shape.