Volume Light Attributes

Color range attributes

colorRange

The colorRange is the color of the light from the center to the edge of the volume. By changing the values on the ramp (gradient) you can decay or change color along the defined light direction. The right side of the ramp represents the light color at the center of the volume. The left side is the color at the outer boundary. The effect of decay is accomplished by the interpolation (blend) from the inner color to the outer color. The outermost color should be black to avoid a hard boundary at the volume edge.

TipAdvanced ramp features exist. For more information, see the following topics in the Shading guide:

Selected Position

Position of the active color entry in the ramp.

Selected Color

The color of the active color entry.

Interpolation

Controls the way colors blend in the ramp. Select an option from the drop-down list: None, Linear, Smooth, Spline. The default is Linear.

None: There is no interpolation; the different colors show up as different bands in the final texture.
Linear: The values are interpolated linearly in RGB color space.
Smooth: The values are interpolated along a bell curve, so that each color on the ramp dominates the region around it, then blends quickly to the next color.
Spline: This takes into account neighboring indices for a smoother effect.

Volume Light Dir: The direction of the light within the volume. Select an option from the drop-down list: Outward, Inward, Down Axis. The default is Outward.
Outward: Light moves away from the center of a box or sphere and away from the central axis of a cylinder or cone. It behaves like a point light.
Inward: The light direction moves towards the center of the light. This is a special effect that does not simulate an area light, but is instead a simple change in direction used for the light computation.
Down Axis: The light direction is down the central axis of the light. It behaves like a directional light.

NoteShadowing does not work properly for directions other than Outward. It always shadows as if from a point light.
Emit Specular has no effect on Inward lights.
Arc: Use this option to create a partial sphere, cone, or cylinder light shape by specifying a degree of rotation. Values can range from 0 to 360 degrees. The most common settings are 180 and 360, the default. 180 is similar to slicing the light volume in half and 360 is the full light. This option does not apply to the box light shape.
Cone End Radius: This option applies to the cone light shape only. This is the relative size of one end of the cone. At a value of 1.0 it is a cylinder, while at 0 it is a cone.
Emit Ambient: If turned on, light affects surfaces in a multi-directional manner. The default is off.

NoteEmit Ambient may wash out shadows and look flat.
When combined with Emit Diffuse, the lighting of a surface is 50% of the surface/light angle, and 50% in a non-directional fashion. If Emit Diffuse is off then the light is totally omnidirectional.

If Emit Diffuse and Emit Specular are off and Emit Ambient is on, the light behaves like an ambient light with decay and a bounded range. This is quite useful for adjusting lighting. It can be used with negative light intensity to pull light out of defined regions.

Penumbra attributes

Penumbra

This section applies to cone and cylinder light shapes only. This contains attributes for managing the penumbra, the area of partial illumination around the shadow border and the light. Using the graph you can adjust the spread and the dropoff of the light. The left side of the graph represents the intensity at the outer edge of the cone or cylinder and the right side represents the intensity from the center of the beam to the edge.

TipAdvanced ramp features exist. For more information, see the following topics in the Shading guide:

Selected Position: This value affects the active entry in the graph and is represented on the x-axis of the graph.
Selected Value: This value affects the active entry in the graph and is represented on the y-axis of the graph.

Interpolation

This controls the way the values are calculated. Select an option from the drop-down list: None, Linear, Smooth, Spline. The default is Linear.

None: There is no interpolation; the different values show up as different bands in the final result.
Linear: The values are interpolated linearly.
Smooth: The values are interpolated along a bell curve, so that each value on the ramp dominates the region around it, then blends quickly to the next value.
Spline: This takes into account neighboring indices for a smoother effect.