Soft Light


| General | Attenuation | Photon | Render Tree Usage

Category: Light

Shader Family: Light

Output: Color

This light shader implements the characteristics of the selected light source by controlling light functions such as color, spread, shadows, falloff, and so on.




The color of a light controls the color of the rays emitted by the light. The final result depends on both the color of the light and the color of object materials. Objects illuminated by white light appear in their "natural" colors. The specific color channels depend on the selected color model. The slider values range from 0 to 1, but you can enter higher values. For information on using the various color editing tools, see Defining Color Properties.


Controls the intensity of the light color.



Sets the angle (in degrees) of the decreasing light around the spotlight cone.


Controls how raytraced shadows are cast by the selected light. When rendering, these options work in conjunction with the Raytraced options in the mental ray Render Options Property Editor.


Activates the creation of raytraced shadows.


Switches on the transparency factor for the umbra (the main shadow where light is completely blocked by an object). This controls how the shadow blends with the material on which the shadow is cast. An umbra value of 0 means that no light is visible in the shadow area (gives a complete, black shadow) so no light passes through the geometry (unless the geometry is transparent). An umbra value of 1 gives no shadow.

Raytraced Soft Shadows

One of the advantages of using raytraced soft shadows over area lights is that only the shadow is sampled and not the entire render.


The raytraced shadow (on the left) has no umbra and produces hard outlines, whereas the raytraced shadow (on the right) has soft edges (Softness=0.3) and a smooth degradation (Samples=32).


The amount of blurring of the shadow edges into the material on which the shadow is cast. A value of 0 (zero) disables the raytraced soft shadows feature.

For spot and point lights, Softness is a maximum jitter distance. The light is moved to a different position within a sphere on every shadow sample.

For infinite lights, Softness is treated as an angle for rotating the light direction. At 0, shadows are crisp with no penumbra while at 90, shadows are very soft. In addition, shadows are softer the greater the distance between the caster and receiver but they do not depend on the position of the light. A value between 0.5 and 1.5 tends to give sun-like penumbras.

Softer shadows generally require more Samples to avoid a grainy appearance.


Specifies the number of times the light ray samples points on the surface, casts shadow rays and returns illumination from the points: a low value is grainy; a high value is smooth, but also takes longer to render. A value of 0 (zero) disables sampling.


Flat Light Mode

Turns the light into an ambient light. For more information, see Creating Flat Lights.


The attenuation options control how light intensity decreases over distance and the shape of the light. This mimics the way light behaves naturally. These options work only with point and spotlights, as well as point and spotlights defined as area lights.

A light's falloff parameters are sometimes defined in conjunction with a volume shader to create an atmosphere such as in a smoky bar or a heavy fog (see Volume Effects). You can also apply a volumic property to the light as described in Applying a Volumic Light Property. Yet another option is to use the Fast Light Effects shader that has a variety of built-in light effects with which you can experiment.

Distance Attenuation

You can set the distance at which the light begins to diminish, as well as the distance at which the falloff is complete (darkness). In addition, you can control how quickly or slowly the light diminishes.

Light Falloff

Activates the fading of light intensity over distance.


Specifies how Falloff is calculated over the specified distance.

  • Use Light Exponent: Uses an inverse square algorithm to calculate the fading of light intensity between the start and end points. The farther light travels from the start point, the more rapidly it looses its intensity. This provides a more sudden transition to 0 (end).

    This option uses the light's Exponent value to determine the falloff. The default value is 2. A high value such as 5 causes light to fall off very quickly, whereas a smaller value such as 0.1 makes the falloff more gradual.

  • Linear: Uses a linear algorithm to calculate the fading of light intensity between the start and end points. The intensity of light diminishes at a constant rate between start and end points. This provides a smoother and more gradual transition to 0 (end).

Start Falloff

Specifies the point at which the light intensity starts to decrease in all directions. Measured in SOFTIMAGE units.

End Falloff

Specifies the point at which the light intensity reaches 0. Measured in SOFTIMAGE units.

Start and End Falloff values using a point light: umbra = 0; bottom corner of chess board is 0; top, left corner is 10.


Start falloff = 0 and End falloff = 4


Start falloff = 0 and End falloff = 8


Start falloff = 6 and End falloff = 8

Shape Attenuation

The shape attenuation options in the soft light shader allow you to define and animate the shape of the light.


Enables the shape attenuation options.


Sets the roundness of the light's cross section. A value of 1 is a circle, and values less than 0.167 are rectangular.

Shape X, Y

Sets the width (in X) and the height (in Y) of the light's shape.

Edge Falloff X, Y

Sets the width (in X) and the height (in Y) of the light's edge shape.


Use Light Color as Energy

When on, uses the light's color as the color for any photon effects.

Energy Factor

Defines the light intensity when the light is used for photon effects (global illumination and/or caustics).

Render Tree Usage

The default Soft_Light shader is connected to every light to give it a color, falloff and cause it to create shadows. You can also use a Color Correction, Invert, or any other type of Image Processing shader to fine-tune or alter the light effect. Make sure it is the last shader connected to the Light Shader input. This shader is useful for applying other shader effects to a light. Expand this shader in the render tree, and notice how it accepts color, boolean and scalar inputs. You can control the color with a texture, use a 2D gradient to control intensity, or use the Change Range shader to control the Start and End falloff distances.

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