Why is a choke not required in high pressure MBFT lamps?

Why is a choke not required in high pressure MBFT lamps?

• A. They are ballastless
• B. They are ballasted by a tungsten filament and don't need control gear
• C. They require an external choke
• D. They rely on an electronic ballast

Answer: (B)

The main idea is that current control and ignition are provided by the lamp itself. In these high-pressure MBFT lamps, the tungsten filament is in series with the discharge and acts as a ballast by its own resistance, limit­ing the current during start-up and throughout operation. That filament also preheats the electrodes to help ignition, giving a reliable strike without needing separate control gear. Because the filament handles current limiting, an external choke or ballast isn’t required, nor is an electronic ballast needed for normal operation.

The main idea is that current control and ignition are provided by the lamp itself. In these high-pressure MBFT lamps, the tungsten filament is in series with the discharge and acts as a ballast by its own resistance, limit­ing the current during start-up and throughout operation. That filament also preheats the electrodes to help ignition, giving a reliable strike without needing separate control gear. Because the filament handles current limiting, an external choke or ballast isn’t required, nor is an electronic ballast needed for normal operation.