Maya 2012 Tutorial
How to Add Volume Lights in Maya
Volume Lights are unique in that the light's illumination is based on one of four shapes. You can specify that the light is either a Box, Sphere, Cylinder or Cone. Within each shape is a small sphere to indicate the actual light source (provided the Volume Light Direction is set to to Outward or Down Axis). Volume Lights are like a three dimensional Area Light.
Once you get the hang of Volume Lights, you will find them to be very creative light sources.
Add a polygon plane to the scene by choosing Create > Polygon Primitives > Plane.
Add a volume light by choosing Create > Lights > Volume Light.
In the Front view, move the light upward with the Move tool (w key). The light's center sphere should be above the plane.
Use the Scale tool (r key) to enlarge the light beyond the plane.
Select the light and open the Attribute Editor.
The Volume Light Attributes section allows you to set the light Color, Intensity and Shape. Shape options include Sphere, Box, Cylinder and Cone.
In the Color Range section you can continue to fine tune the light's decay with the Gradient and Interpolation settings.
The Volume Light Direction menu includes Outward (from the center sphere), Inward and Down Axis (pointing down from the center sphere).
For Cylinder and Cone lights you can make adjustments in the Penumbra section.
The Light Effects section is used to create Fog and Glow.
In the Shadows section you can choose between Depth Map and Raytrace Shadows.