Which of the following is a gas discharge lamp type mentioned in the material?

• A. HMI
• B. LED
• C. Tungsten
• D. Fluorescent

Answer: (A)

Gas discharge lamps generate light by driving electricity through a gas or vapor, creating an arc that excites atoms to emit light. HMI, which stands for Hydrargyrum Medium-arc Iodide, is a metal-halide high-intensity discharge lamp. Its arc uses mercury vapor with metal-halide salts inside a quartz tube, producing an extremely bright light with a daylight-like color balance. This combination and operating principle make HMI a classic example of a gas-discharge lamp type highlighted in the material.

In contrast, tungsten lamps rely on a heated filament (incandescent), LEDs are solid-state diodes, and fluorescent lamps also use a gas discharge but are categorized separately due to the phosphor conversion process they employ. The material’s listing identifies HMI specifically as a gas-discharge type, which is why it’s the best choice here.