I've just downloaded a free excel program called SPOT: Sensor Placement &
Optimization Tool. This may not be news to some, but It won the most
innovative product of the year at the 2008 LightFair International. It's
from Architectural Energy Corp. (www.archenergy.com) and is meant to "assist
a designer in quantifying the existing or intended electric lighting and
annual daylighting characteristics of a given space" and optimally locating
the photo sensor.

For locations outside the U.S., it even uses Energy Plus Weather (ERW)
files. You can get more information at www.archenergy.com/SPOT

Paul Hay