12.3.1 Spot light attributes

The attributes supported by Iray for Maya are Color, Intensity, Cone Angle and Dropoff. All other attributes in the Spot Light will be ignored by Iray.
Spot Light Attributes section in the Attribute Edtior of the Maya Spot Light
Adjust the color of the emitted light
Adjust the intensity of the emitted light
Spot Lights in Maya are able to send out light without light decay. This is different in Iray for Maya because in reality light always has a decay over the distance. So it is usually necessary to increase the intensity of the Spot Light to see any lighting effect.
Cone Angle
Defines the angle (in degrees) from the edge to the edge of the spot light's beam.
Controls the rate at which light intensity decreases from the center to the edge of the spot light beam.
Spot Lights rendered with Iray for Maya 2.0 will only cast hard shadows.