A light emitting diode (LED) signal with an LED light output monitoring sensor. If the LED light output drops below a pre-set level, an output signal of the sensor via a comparator and deactivation circuit, deactivates one or more LEDs creating a visible fault display aspect, thereby visually indicating...http://www.google.com/patents/US6667623?utm_source=gb-gplus-sharePatent US6667623 - Light degradation sensing led signal with visible fault mode
