Not to fuel the fire but Toyota calls them solar sensors. A vehicle with dual zone auto a/c will have 2. A vehicle with manual a/c will have 1. Toyota also uses a separate ambient light sensor for auto headlights.
My only gripe with the Subaru system is it has no delay for auto headlights. This causes the lights to come on anytime the sensor has any sort of coverage. I live in a large metro area and commute on the interstate. At 80 mph going under an overpass it just looks like I'm flashing my lights at the car in front. With the separate sensor Toyota has built in a 2-3 second delay to stop the above from happening.