Magnetically Regulated (Mag Reg) and Regulated Lag (Reg Lag) are another type of EM (Electromagnetic Ballasts) HID ballasts. This ballast design is the most sophisticated and provides the highest power regulation to the lamp. They utilize a magnetic with three separate coils. The following schematic shows the Magnetic Regulator (Regulated Lag) HID Ballast Circuit Diagram. This circuit can operate at a variety of line voltages by usingthe different Line V transformer tap locations.