Minecraft wiki entry for Daylight_detector, associated text: The daylight sensor can be placed on top of TNT unlike most redstone devices. If planted at about midnight, this can make for an excellent timebomb, as the TNT ignites when the sun rises. Since the skylight is measured, which is shadowed out by blocks above, the sensor on TNT can be used in traps for players breaking the (e.g. ore or cake) blocks above the sensor. The Daylight sensor bomb can be rigged to go off at different times. If you want it to go off during the day, wire redstone to the TNT from the daylight sensor. While you can just place the sensor on top of the TNT, the TNT glitches to cause the TNT to appear above the daylight sensor. For a bomb to go off during the night, a NOT Gate is needed. Other than that, it is the same. For a bomb to go off at noon, you need a redstone comparator. The daylight sensor goes through the TNT, but because the lever is always full power, and the daylight sensor gets best power at noon, the bomb explodes at noon.