At a fixed voltage, the current flowing through the LEDs can vary dramatically depending on the forward voltage of the individual LED array. For instance, the example here shows that the minimum, typical, and maximum currents for a 400 lumen cool white LED Array with an applied voltage of 8.4 V could be 0 mA, 70 mA or 300 mA, respectively, depending on the forward voltage of the array. If this voltage was applied to adjacent LED Arrays, one would appear to be out (0 mA), one dim (70 mA) and one bright (300 mA).  It is for this reason that the LED manufacturers recommend against driving LED arrays with constant voltage sources or connecting multiple LED arrays in parallel.