Liquid Penetrant Testing Level 2 (PT-2) Practice Exam

At what supply voltage do mercury vapour black lights tend to extinguish?

1. 120 volts

2. 90 volts

3. 220 volts

4. 200 volts

The correct answer is: 200 volts

Mercury vapor black lights are specifically designed to operate within a certain voltage range to ensure optimal performance. Typically, these lights can extinguish when the supply voltage drops below a certain threshold — in this case, around 200 volts. If the voltage supplied is lower than this level, the electrical discharge necessary to excite the mercury vapor may not occur effectively, leading to a decrease in light output or complete extinguishment. Understanding the functioning of mercury vapor lamps is essential for their effective use in applications like liquid penetrant testing, where proper illumination is crucial for detecting surface defects. It is important to recognize that the correct voltage is critical for not only lighting performance but also the durability and lifespan of the equipment. Hence, operating at or above 200 volts ensures reliable functionality of the black lights in field applications.