As previously mentioned, a designer could use a ballast resistor for each string, which is an inexpensive and simple solution. But, this design is inefficient and does not provide great current balancing between strings. Placing LEDs in parallel is difficult because of the variation in forward voltage from one device to the next, due to process variation increases. As a result, the forward voltage of each LED (VLED) will be different for each string in the LED array. If a designer only uses a ballast resistor for each string, the one with the highest forward voltage will receive the lowest share of current while the string with the lowest forward voltage will receive the highest share of current. Hence, the brightness through each string will not be matched. In addition, each ballast resistor is dissipating energy, and therefore heat, resulting in lower efficiency and lower system reliability.