14 Ballast

All Gas Discharge lighting operates on the principle of passing an electric current through an arc chamber containing some kind of gas which reacts to the moving electrons by emitting waves of visible light.

Standard voltages are generally unacceptable for operating these types of lamps, so a ballast is required to supply the appropriate striking voltage, and also to limit the current once the arc is established.

When a discharge lamp is first energized, the air gap is a very high resistance path, and so it takes a massive burst of voltage to convince the electrons to make the leap from one end of the lamp to the other.  Once the arc is established, however, it is a very low resistance path, and so the ballast must limit the current to a safe level to prevent the lamp from drawing too much current and damaging itself. This is the main function of all ballasts: to provide high initial striking voltage to establish the arc, and then to limit the current once the arc is established.

There are several types of ballasts, ranging from simple core and coil ballasts to more complex and modern electronic ballasts, and each ballast must be matched with the type of lamp that it is set to control. Mismatched lamps and ballasts can result in numerous problems, such as reduced light output and reduced lamp and ballast life.

When replacing older core and coil ballasts with newer electronic ballasts, care must be taken to properly dispose of the old equipment. Many older ballasts are filled with oil, and some may contain toxic PCBs, which are a health hazard. This oil is intended to help regulate the internal temperature of the ballast. Care should be taken to avoid contact with the skin if a ballast shows signs of leaking or has been subjected to severe overheating.

As a rule, a 10°C rise in operating temperature above the rated ambient operating temperature will shorten a ballast’s useful life by 50%.