Minecraft wiki entry for Redstone_components, associated text: A powered redstone comparator turns ON redstone dust, a properly-facing redstone comparator or redstone repeater, or a mechanism component in front of it; or strongly powers an opaque block in front of it – all at the same power level as its input signal (unless modified by a side signal, see below). It has no effect on blocks in other adjacent positions (including the block beneath it).