LONG-LASTING RELIEF: Ultrasonic cool mist technology safely moisturizes the air for 10 to 24 hours of continuous operation (depending on mist control setting) so you can breathe easily and get more restful sleep 1 GALLON WATER TANK: Large tank and powerful steam output provides ideal coverage for large bedrooms, offices, and other rooms up to 500 square feet OPTIONAL NIGHT LIGHT: Offers soothing lighting for maximum relaxation and operation in the dark (choose between blue, green, and red) AUTOMATIC SHUT-OFF: Safely turns humidifier off when water level is low or the water tank is removed