Question T6B07
From subelement T6 - T6B
What causes a light-emitting diode (LED) to emit light?
Why is this correct?
LEDs emit light when forward DC current flows through them in the proper direction - from anode to cathode. Like all diodes, LEDs only conduct when forward-biased (positive voltage on anode). Reverse current (B) would block conduction entirely. RF signals (C and D) are alternating current and wouldn't provide the steady DC flow needed for consistent light emission.
Memory tip
Remember: LEDs are diodes first, lights second. They follow all diode rules - forward bias conducts, reverse bias blocks. The light is simply a bonus effect when current flows in the forward direction through the semiconductor junction.
Learn more
In practical amateur radio operation, LEDs serve as visual indicators throughout your equipment - power lights, S-meters, frequency displays, and SWR indicators. They're preferred over incandescent bulbs because they consume less power, generate minimal heat, and have longer lifespans. Understanding that LEDs require forward DC current helps when troubleshooting indicator circuits or designing control panels for homebrew equipment.
Think about it
Why do you think LEDs won't work properly if you accidentally connect them backward in a circuit, and what would you observe?