Which of the following is a HID lamp type?

• A. Low pressure sodium
• B. LED lamp
• C. Compact fluorescent
• D. Incandescent lamp

Answer: (A)

High-intensity discharge lamps produce light by passing an electric arc through a gas or vapor inside a sealed arc tube. Low-pressure sodium lamps fit this category because they generate light from an arc in sodium vapor at low pressure, delivering very high efficiency but a distinctive orange-yellow color with poor color rendering. The other options rely on different mechanisms: LEDs emit light from semiconductors, incandescent lamps light by heating a filament, and compact fluorescents use mercury vapor discharge with phosphors. So, the HID option here is the low-pressure sodium lamp.