The Volume Parameters are located in a volume light’s Control Window (see Use the control window).

Volume lights have many parameters which define the shape of the volume and the direction of the light/force in the volume.

Shape

Defines the shape of the volume light as either a BOX, SPHERE, CYLINDER, CONE, or TORUS. The default setting is SPHERE.

You can also use the Transform tools to position or reshape a volume light. Apply the Transform to the light icon in the modeling window or to the DAG node above the light in the SBD window.

Specular

Makes the light contribute to the specular component. (If the Intensity value is negative, set SpecularOFF.) The default setting is ON.

Decay

Controls how quickly the light intensity decreases with distance within the light’s volume. (The volume light Decay parameter differs slightly from the Decay parameter for other light types.) The slider range is 0 to 10. The default value is 1.

0	No decay (light reaches everything within the volume and nothing outside).
> 0	Light intensity decreases from the center to the edges of the volume. For example, a value of 0.5 produces a linear dropoff from the center to the edges. With a value close to 1, intensity drops off very fast from the middle. With a value close to 0, intensity drops off slowly in the middle and fast near the edges.
< 0	Light intensity decreases from the edges to the center of the volume.

The direction that light decays depends on the volume light’s Shape setting.

Shape	Decay Direction
BOX and SPHERE	all directions from the center
CYLINDER and CONE	in the direction of the principal axis
TORUS	perpendicular to the principal axis

If Emit Particles is ON under Active Effects, the Decay value controls where within the volume the particles are emitted. For large positive values of Decay, particle emission is concentrated in the center of the volume. For large negative values, particle emission is entirely on the surface of the volume.

If Force is set (that is, not OFF) under Active Effects, the Decay value controls how quickly the force intensity decreases with distance within the light’s volume.

Decay Start

Defines how far out from the center of the volume the light intensity begins to decay. The slider range is 0 to 1. The default value is 0.

Dropoff

Controls the rate at which light intensity decreases from the principal axis to the edge of the light for CONE and CYLINDER volume lights only. The slider range is 0 to 10. Typical values are between 0 and 50. Values of 1 and less produce almost identical results (no discernible intensity decrease along the radius of the volume). The default value is 0 (no dropoff). The volume light Dropoff parameter is similar to the spot light Dropoff parameter (see Dropoff).

Dropoff Start

Defines how far out from the principal axis of the volume the dropoff starts. The slider range is 0 to 1. The default value is 0.5.

Torus Radius

The ratio of the minor radius to the major radius for TORUS volume lights only. The slider range is 0 to 0.5. The default value is 0.5 (a typical bagel, where the “hole” is reduced to a single point).

Cone End Radius

The radius of the end of the cone for CONE volume lights only. If the Cone End Radius value is negative, the direction of the cone is reversed. The slider range is 0 (a true cone) to 1 (a cylinder). The default value is 0.1.

Arc

The portion (in degrees) of the swept volume for CONE, SPHERE, TORUS, and CYLINDER volume lights only. The slider range is 0 to 360. The default value is 360 (the entire volume).

Directionality

The proportion of directional light to omnidirectional (ambient) light. The slider range is 0 (light comes from all directions, like an ambient light) to 1 (light comes from one direction only, like a directional light). The default value is 1.