The 100-hour* Ultrasonic Warm and Cool Mist Humidifier by Guardian Technologies guards against problems caused by dry air in the home. It features an easy to fill large 1.5 gallon tank, ideal for use in medium sized rooms. Unlike other humidifiers that grow slimy mold on the water tank surface, Silver Clean Protection is embedded in the tank to fight the growth of mold and mildew on the surface of the water tank. Thanks to ultrasonic technology, it disperses a fine mist into the air, and is ultra-quiet making it ideal to have on while you sleep. The humidifier is equipped with the option for warm or cool mist, a night light and variable mist control. A low water indicator light lets you know when it's time to refill the water tank.