12.1.1 Directional light attributes

The attributes supported by Iray for Maya 2.0 are Color and Intensity. All other attributes in the Directional Light will be ignored by Iray.
Attributes in the Attribute Edtior of the Maya Directional Light
Adjust the color of the emitted light.
Adjust the intensity of the emitted light.
Directional Lights in Maya have no light decay. This is different in Iray for Maya because in reality light always has a decay over the distance. A Directional Light rendered with Iray for Maya always has light decay. So it is necessary to increase the intensity of the Directional Light to see any lighting effect.
Directional Lights rendered with Iray for Maya 2.0 will only cast hard shadows.