I don't know where you'd find a ready-made 4 quadrant light sensor, but it ought to be easy to build using a lens (perhaps a round Fresnel lens) and a home-made quadrant baffle using thin wood or foam-core sheets and a plastic bowl painted flat black. The RCTIME in Stamp Basic can be used to measure the light intensity in each quadrant (one at a time, but fairly quickly). Read the Stamp Basic Manual chapter on the RCTIME statement for details. There may be useful information also at www.emesystems.com at the "app-notes" link at the bottom of the page.
Comments
The Nuts and Volts Column #6 deals with controlling relays, solenoids, and small motors with Stamps.
The index is here:www.parallax.com/Resources/NutsVoltsColumns/tabid/272/Default.aspx