NALMCO Certified Apprentice Lighting Technician (CALT) Practice Exam

If you replace an HID lamp with another HID lamp type, which of the following are you most likely to have to replace as well?

1. The luminaire

2. The pole if it's mounted on one

3. The ballast

4. The nearest circuit breaker

The correct answer is: The ballast

When replacing an HID (High-Intensity Discharge) lamp with another type of HID lamp, it is crucial to consider the compatibility of the lamp with the existing ballast. HID lamps require specific ballasts to operate correctly, as the ballast controls the electrical supply to the lamp. Different types of HID lamps, such as metal halide, high-pressure sodium, or mercury vapor, typically have different electrical requirements in terms of voltage and starting methods. Therefore, if you switch to a different type of HID lamp, you will most likely need to replace the ballast to ensure that the new lamp operates properly and safely. The luminaire, which houses the lamp, may not necessarily need to be replaced unless it is specifically designed for only one type of HID lamp. The pole does not change with the type of lamp used; it is simply a support structure. The circuit breaker generally does not need replacement unless it is not rated for the load of the new system or there is a specific issue with the circuit itself. Thus, ensuring compatibility with the ballast when changing HID lamp types is the key reason why replacing the ballast is often necessary.