You can now import .IES photometric files into Cycles with this new add-on by Lockal.
Ray Tracer writes:
Great news for all the ArchViz people using blender Cycles!
Lockal released an useful add-on for importing and using real photometric (.IES) lamps directly in Blender Cycles. As a bonus you can select the colour temperature of the lamp in Kelvin!
After installation of this addon new item "IES To Cycles" appears inside "File" -> "Import" menu (also don't forget about space menu).
This add-on both works with standard and latest development releases.