Visible Light Paths

Visible Light Paths

Visible Light Paths

View spot light beams as if shining in a hazy room.

This feature creates a transparent lamp beam with a pattern to emulate light passing through a smoky or foggy room.

You can define a visible light beam on the spot-light creation wizard.


Lamp beam wizard.jpg

Beam and Field angle - these are set to the same value to make a tight beam of light.
Lamp Length - the length of the lamp itself.
Beam Length - the length of the lamp beams.

This should be long enough to pass through the wall or screen which receives the light paths.

No. of beams - creating 2 or 3 beams will produce a more realistic effect.

If you use multiple beams, see: Refraction issues below.

Total sub-beam width - the percentage of the full beam angle which is divided between multiple sub-beams.
Total Transparency - this is divided by the number of beams.
Haze Patterns one or more patterns can be applied to emulate a haze effect. See: Procedural Bump Patterns below.

Procedural Bump Patterns

You may select one or more patterns to place on the light beam.

The patterns are all created with default strengths and other settings. If you want to modify them, right click on the beam and edit its material directly.

Sandpaper pattern on light beam.
Rubble pattern on light beam.
:Wrinkled pattern on light beam.
Marbled pattern on light beam.
Pyramid pattern on light beam.
All 5 patterns on light beam.

Note: It sook 1 minute 16 seconds to render this image with just one pattern, and 2 miniutes and 18 seconds to render it with all 5 patterns.

Refraction issues

There is a setting in IRender nXt, Refraction Bounces, which determines how many transparent surfaces will be processed for transparency and refraction. The default for this setting is 6.

Refractive Bounces on the Render tab of the Setup Dialog.

Refreactive Bounces.jpg

If you use 3 sub-cones for your domes that means that light and colors passing through a single light fixture will need 6 refraction passes. If there are two light beams - one behind the other - then the second light beam will be opaque where it appears behind the first light beam - because all 6 refractions were used up for the first light beam. So you would want to change this refraction setting to 12 to process overlapping visible light paths.

Similarly, if you were to place 6 sub-beams in a single light, then 12 refraction passes would be required to see lights and colors from behind the 12 surfaces.

Visible Light Paths processed with 6 refractive bounces.


The lamps have 1,2,3,4,5 and 6 sub-beams - from left to right.
The lamps with 4 or more sub-beams require 8, 10 and 12 refractive bounces in order to be transparent.

Visible Light Paths processed with 12 refractive bounces.


The lamps with 4 or more sub-beams are now transparent.
However it took longer to render.

Note: It there are visible light paths behind each other you will need even more refractive bounces.

See also