LEDs as light sensors

3 LEDs as light detectors using reverse bias. An AVR reads each of the 3 LEDs reverse currents as voltage accross a large resistor. When the LEDs reverse current is below a certain level it is considered dark or shadowed and is flagged to be lit up after the cycle is completed. There is thus a short period when the LED is changed from being the detector into an emitter by switching the polarity of the supplied voltage. The apparent flashing is due to noise and the time pr cycle of the AVRs ADC cycle.