Ballasts & Power Supplies UV Ultraviolet Lamps and Bulbs

An electrical ballast is a device intended to limit the amount of current in an electric circuit. Ballasts vary greatly in complexity. They can be as simple as a series resistor as commonly used with small neon lamps or light-emitting diodes (LEDs). For higher-power installations, too much energy would be wasted in a resistive ballast, so alternatives are used that depend upon the reactance of inductors, capacitors, or both. Finally, ballasts can be as complex as the computerised, remote-controlled electronic ballasts now often used with fluorescent lamps.

Ballasts are used where a load does not regulate its own current consumption well enough. These are most often used when an electrical circuit or device presents a negative (differential) resistance to the supply. If such a device were connected to a constant-voltage power supply, it would draw an increasing amount of current until it was destroyed or caused the power supply to fail. To prevent this, a ballast provides a positive resistance or reactance that limits the ultimate current to an appropriate level. In this way, the ballast provides for the proper operation of the negative-resistance device by appearing to be a legitimate, stable resistance in the circuit.

Examples of such negative-resistance devices are gas-discharge lamps. All gas discharge lamps require a stable ballast for continuous operation. The type of ballast that a discharge lamp requires is called an inductor. An inductor is very common in line-frequency ballasts to provide the proper starting and operating electrical condition to power a fluorescent lamp or a high intensity discharge (HID) lamp. (Because of the use of the inductor, such ballasts are usually called magnetic ballasts.) The inductor has two benefits:

Its reactance limits the power available to the lamp with only minimal power losses in the inductor
The voltage spike produced when current through the inductor is rapidly interrupted is used in some circuits to first strike the arc in the lamp.

A disadvantage of the inductor is that current is shifted out of phase with the voltage, producing a poor power factor. In more expensive ballasts, a capacitor is often paired with the inductor to correct the power factor. In ballasts that control two or more lamps, line-frequency ballasts commonly use different phase relationships between the multiple lamps. This not only mitigates the flicker of the individual lamps, it also helps maintain a high power factor. These ballasts are often called lead-lag ballasts because the current in one lamp leads the mains phase and the current in the other lamp lags the mains phase.

Electronic Ballasts
Electronic ballasts have almost become the standard in the low pressure lamp lighting industry. They allow energy and financial savings in many applications. The lamp operation is free from flicker and the ballast produces virtually no noise or hum. The incoming 50 Hz power (240 volts) is converted to high-frequency AC (usually 20 to 40 kHz). This leads to a constant gas discharge compared to conventional ballasts and prevents cathode flicker. Electronic ballasts are more efficient than magnetic ballasts in converting input power to the proper lamp power. The operation of low pressure, amalgam ultraviolet UV lamps at higher frequencies reduces end losses, resulting in an overall lamp-ballast system efficiency increase of 15% to 20%. Electronic ballasts are directly interchangeable with magnetic ballasts. They operate with most ultraviolet UV lamps available.Special electronic ballasts can operate two or four lamps reducing the total number of ballasts in a system. This also reduces installation and field wiring costs. Other advantages are reduced weight, less heat and noiseless operation and reduced lamp flicker. Infralight supplies a comprehensive range of ballasts and HID power supplies for low pressure germicidal and medium pressure lamps.