Directional Lights and Mental Ray
Maya 2012 Tutorial
How to Add Directional Lights for a Maya Mental Ray Render
Directional lights are unique because they project a series of parallel light rays. So you need to be careful as you set the light's direction.
Since directional lights don't have a decay attribute, it doesn't matter where you place the light in the scene. All objects in the scene receive the same light intensity with no soft falloff on the edges. Because of these qualities, they work great as a sun light.
Raytraced directional light shadows tend to look better than Depth Mapped shadows.
Add a NURBS sphere to the workspace by choosing Create > NURBS Primitives > Sphere.
Add a floor to the scene by choosing Create > Polygon Primitives > Plane.
With the plane selected, click the Scale tool (r key) and resize the plane several times larger than the sphere.
Using the Move tool (w key), position the sphere above the floor object.
Select the sphere, then right click the sphere and choose Assign New Material > Blinn.
With the sphere selected, open the Attribute Editor. Click the Blinn tab, Color rectangle to change the sphere color to blue.
Activate Mental Ray by clicking the Render Settings icon and choosing Render Using: Mental Ray.
Click the Quality tab and choose Quality Presets: Production.
Add a directional light by choosing Create > Lights > Directional Light. Use the Move tool (w key) to move the light above the scene.
With the directional light selected, use the Rotate tool (e key) to set the light's direction.
To activate Raytrace Shadows, select the light and open the Attribute Editor.
Open the Shadows section, Raytrace Shadow Attributes sub-section and click the Use Raytrace Shadows checkbox.
Increase the Shadow Rays to 30 and render your image by clicking the Render Current Frame icon.
To soften the shadow, return to the light's Raytrace Shadow options in the Attribute Editor and increase the Light Angle value to 5.
Turning the Light On and Off
In the light options you can turn your light on or off by selecting the Illuminates by Default checkbox.
Don't forget the Light Color
Light color works wonders to set the tone and mood of your scene. For example, a warm yellow conveys a different mood than a cooler blue or blue/green color.
Can't Find Mental Ray?
If Mental Ray doesn't appear in the Render Settings, Render Using: menu, choose Window > Settings/Preferences > Plug-in Manager. Make sure Mayatomr.bundle is loaded.