Question T6D07
From subelement T6 - T6D
Which of the following is commonly used as a visual indicator?
Why is this correct?
LEDs (Light-Emitting Diodes) are specifically designed as visual indicators that emit light when forward current flows through them. The other options are primarily switching or control devices: FETs are field-effect transistors used for switching and amplification, Zener diodes regulate voltage, and bipolar transistors provide amplification or switching. Only LEDs have the primary function of producing visible light for indication purposes.
Memory tip
Look for components whose names directly describe their function. 'Light-Emitting' in LED immediately tells you it's for visual indication. When a component's name includes its purpose (like 'Light-Emitting'), that's usually the key to identifying its primary function on exams.
Learn more
LEDs are fundamental indicator components in amateur radio equipment, appearing as power indicators on transceivers, SWR meter displays, and antenna tuner status lights. They convert electrical energy directly into photons through electroluminescence in semiconductor junctions. Modern amateur equipment extensively uses LEDs because they're efficient, long-lasting, and can indicate multiple states through different colors or brightness levels.
Think about it
Why do you think amateur radio equipment designers choose LEDs over incandescent bulbs for most indicator applications in modern transceivers and accessories?