Opu White Ultrasonic Aroma Diffuser by Serene HouseThe Opu Ultrasonic Cool Mist Diffuser. The new easy fill lid allows you to add water straight from the top of the cover. Water will flow from the openings in the Opu's lid down into the water tank. A window on the front of the unit lets you see the water level without removing the cover. Opu has three operating modes. 8 hour low mist continuous mode, a 6 hour high mist continuous mode, or a 14 hour intermittent low mist mode. Seven soft LED ambient