** This latest version disables (locks) the attributes of the base Maya area light that are not used **
Creating a Photometric light in Maya is unnecessarily complex. There are quite a few steps and that process can get old real quick. This script will create the whole setup in just one click.
This creates an Area Light and converts it into a spherical shaped mental ray Area Light (but you can make whatever changes you want after its created) and it attaches an mia_photometric_light node to the light shader and photon shader and sets it up for 139cd intensity (100 watt light bulb). It assumes your units are set to centimeters (Maya default). To soften the shadows you must adjust the scale of the Transform node.
It is recommended to use an exposure control when using the mia_photometric_light node because it always uses an inverse square (quadratic) decay rate.
10/2/2012 -- UPDATE: Autodesk has reportedly fixed the soft shadows and caustic photons bugs for mia_photometric_light in the lastest update for Maya 2013!