dark zones also influence the spacing between leds, which is typically between about 9 mm and 11 mm; placing leds farther apart creates more pronounced dark zones. this, in turn, limits the ability of designers to reduce the number of leds in a display despite the cost advantages and increased energy efficiency of such a reduction. furthermore, the poor light-mixing of current light guides makes digital displays highly sensitive to variations in led color and brightness. closely packed leds can also create thermal management issues.