Minecraft wiki entry for Redstone_components, associated text: For opaque mechanism components (command blocks, droppers, dispensers, note blocks and redstone lamps), it's important to make a distinction between a mechanism component being activated (so that it performs an action) and being powered (so that a redstone signal could be drawn from it by a transmission component). Any method of powering a mechanism component (such as a redstone torch underneath it) also activates it, but some activation methods (such as a redstone torch next to or above a mechanism component) does not actually power the component (following the usual rules for power components).