The challenge is to provide a system that will function in a country with a somewhat unstable power network equally as well as in a country with a very stable power network, such as in the United States or Canada. Traditionally, manufacturers have used simple electromagnetic devices or ballasts, which incorporate electrical wires wound around a ferrite core. The number of windings determines the output current delivered to the lamp. The ballast also incorporates a starter to physically generate enough starting voltage to vaporize the mercury enclosed inside the low-pressure UV lamps. This all sounds relatively simple and in fact it is, as long as both the input voltage and input frequency remain constant.
Magnetic ballasts suffer from a multitude of pitfalls.
Although the cost of a magnetic ballast is relatively low, its use in the design of UV systems offers many obstacles. If the temperature rises above this optimum, the resistance of the lamp changes, altering the voltage and current supplied by the ballast. The result is lower UV output and ultimately a lower UV dose. In low-temperature situations, the lamp may experience difficulty in starting. In order for manufacturers to offer a variety of models with different flow rates, it is necessary to use UV lamps of varying lengths.