How do I create visible light beams?

Here it is an extract from a discussion between Charles Blaquiere and P.Sauvageau:

PS>     I have find that the best way to make visible light is to use
PS> conical shaped bright objects. I use linear texture to augment
PS> transparency along the y axis, so the cone is semi-transparent
PS> (160-160-160) at the source and full transparent (255) at the end.

CB>     In addition, you could use the Ghost or Fakely textures; they
CB> would give you more control over the transparency falloff. This is
CB> off the top of my head, BTW; I haven't actually tried it to see if
CB> it gives better/worse results than plain ole fog.

PS>     One thing that I have done is to use FilterNoize applied on a
PS> parent axis, with "Apply to children".  When I rotate the light
PS> cone, I do not move the parent axis.  This way, you will see the
PS> light beem moving in an immobile cloud of irregular smoke or fog.
PS>     One of the problem I encoutered is that Filter Noise seem to
PS> override the linear transparency setting, so the beem do not appear
PS> to vanish as it come farther from the light source.

PS>     A conical lightsource is cast in the Y axis direction and the
PS> linear texture extend in the Z direction, so you will have to rotate
PS> the texture axis to have it's Z pointing in the same direction as
PS> the light source Y axis.  The transition lenght of the texture must
PS> be a little shorter than the lenght of the object or the edge of the
PS> cone will be visible.  Make the cone object transparency to 150, and
PS> the texture 255.  Make the cone object bright.

PS>     A very interesting effect can be made with this kind of light
PS> beem in an animation: I wanted the light beem to appear to be casted
PS> through smoke or fog.  I applied a pastella texture on the cone to
PS> make it appear to be more irregular, but when the light move, the
PS> effect look verry artificial. So I added a parent axis to the light.
PS>     This axis have the pastella texture with "apply to children"
PS> property. To animate the light beam, I moved it in the cycle editor,
PS> while keeping the parent axis untouched.  When animated, the light
PS> beem seem to move in an immobile cloud.

Last Update: July 13, 1995
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