NALMCO Certified Apprentice Lighting Technician (CALT) Practice Exam

If a pulse-start MH lamp experiences a momentary power interruption, how long does it take to re-strike after power returns?

1. Seconds; heat sufficiently

2. Minutes; heat sufficiently

3. Seconds; cool down

4. Minutes; cool down

The correct answer is: Minutes; cool down

When a pulse-start metal halide (MH) lamp experiences a momentary power interruption, it can take several minutes to re-strike after power returns. This is primarily due to the lamp's need to cool down sufficiently before it can start again. A pulse-start MH lamp requires that the particular conditions for re-ignition are met after a power loss, which includes cooling the arc tube to a temperature where the discharge can be reestablished. If the lamp has been in operation and undergoes a brief interruption, the heat within the arc tube may not be sufficient for immediate re-strike, and it can take a longer period—up to several minutes—before the internal gas becomes conductive and the lamp can reignite. This is particularly true in pulse-start systems, where the starting requirements and thermal conditions are critical. Thus, the correct response emphasizes the necessity of cooling down, which is integral for the re-strike process following a power interruption.