I'm trying to render stage lighting using cylindrical light sources and
environmental media.  Spotlights above a stage in a smoky bar, kind of
thing.

The light sources are in the image, surrounded by objects that make them
look like conventional spotlights, and the beams being emitted look
fantastic as do the objects (musicians) they illuminate.  However the light
sources look awful.

Here is a very simple example that exaggerates the problem.  The ends of the
cylindrical lights are rendered as stark black discs.

camera {
  location <0, 0.5, -1> look_at y/3
}
plane {-z, -1 pigment {rgb 1}}   // Backdrop
plane { y,  0 pigment {rgb 1}}   // Floor
// Illuminate the background so that the black discs at the ends
// off the cylindrical lights are more obvious
light_source {<10, 10 -10> rgb 0.3}
// Blue light on left, aimed right, striking the floor:
light_source {
  <-0.5, 0.4, 0>
  color rgb <0, 0, 5>
  cylinder
  parallel
  radius 0.05
  falloff 0.10
  point_at <0.3, 0, -0.1>
}
// Red light aimed nearly at the camera
light_source {
  <0.1, 0.6, 0.5>
  color rgb <5, 0, 0>
  cylinder
  radius 0.03
  falloff 0.07
  point_at <-0.05, 0.35, -1>
}
media { scattering { 2, rgb 1/2 extinction 0} }

I've various ways to replace the disks with illuminating objects, but they
all look awful and I get the feeling I'm just missing something obvious.

Please set me right.  Is there a simple way to remove those black discs?

Many, many thanks in advance.

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