Ballasts: 2 of 21

Ballasts can be either electromagnetic (transformers with iron cores and copper windings) or electronic. Note that electromagnetic ballasts are sometimes simply called magnetic ballasts.

Electronic ballasts are (1) lighter weight and smaller size than electromagnetic ballasts (2) increase system efficiency because they dissipate less power themselves and manage to squeeze out more light from the discharge (3) operate at very high frequencies (typically 20,000 cycles per second and more) thereby eliminating strobe and ballast hum.

HID ballasts can be electronic if they are low wattage, but are generally electromagnetic if they are higher wattage (175 and above.)

Many ballast are encased in a metal box and filled with potting compound. This makes them less noisy (remember transformers hum?) and also provides electrical insulation.