Stack light are indicators that indicate the operating status of machinery, systems, etc. using multiple colored indicator lights. Many display units have 1 to 5 tiers of vertical types with freely changeable color arrangement, and the number of colors to be used, the stacking order, and the number of tiers can be set according to the device or system. Light sources include LEDs and light bulbs, and body shapes include round, square, pole types, etc. In addition to the normal lighting function, there are those that flash or rotate, others that emit a buzzer, others that can display processes such as operating time and remaining battery level, etc. Many products have antifouling properties that can be used in factories where oil mist or dust is generated, have impact resistance that is suitable for installation in equipment with vibration, etc., and there are products with energy-savings in mind.