A self-contained system uses light reflectivity to examine intensity of a dyed
spot on a device membrane surrounded by background area to discern information
about the specimen that produced the spot. In a preferred embodiment, a master
clock alternatively drives one LED focussed upon the spot center, and then drives
two LEDS focused on the background area. Light reflected from the spot and background
is detected by preferably two photodetectors ("PDs") spaced-apart a multiple of
90 azimuthal.