In order to ensure all welded and brazed joints are liquid tight, what power rating must the lamp used for the light test have at minimum?

The correct choice is a power rating of 100 watts for the lamp used during the light test to ensure that all welded and brazed joints are liquid tight. This wattage provides sufficient intensity to clearly identify any potential leaks in the joints by illuminating them effectively. A 100-watt lamp produces a bright enough light to highlight any imperfections or gaps that might not be visible with lower wattage, enabling a thorough inspection to confirm the integrity of the joints.

Lower wattage lamps, unlike the 100-watt option, may not offer adequate illumination, potentially leading to oversight of leaks or weak points. Having a lamp with elevated brightness is especially critical in dim work environments or when inspecting complex or closely spaced joints in HVAC systems. Thus, the 100-watt rating balances effectiveness and practicality in ensuring that all welded and brazed joints are sound and reliable.