status information is provided from an electronic signaling system to an array of n light emitting diodes connected in series between high and low voltage sources , where n ≧ 2 , and where n is selected so that the potential difference between the voltage sources is less than the sum of the cut - in voltages of the n leds in the array . control signals are delivered from the electronic signaling system to the led array over m control lines , each of which is connected between two of the leds in the array . the control signals cause the leds to conduct . the control signals are timed so that the leds in the array conduct one or two at a time .