Microorganisms collect in moist, dark places. When the light remains on, the reproduction of these organisms may be reduced. The method also simplifies the installation. Complex wiring into the fan circuit is eliminated. Isolation relays, sail switches, and pressure switches are not required for installation. The unit plugs into a standard 120-VAC outlet. It is also more energy efficient to leave the bulb on constantly. Similar to fluorescent lights, the energy necessary to switch on the UV bulb is high, while functioning energy is low.