Which of these voltages would you normally choose to cause an LED to light?

The choice of 3 V DC aligns with the typical operating voltage range for many small light-emitting diodes (LEDs). LEDs generally require a forward voltage that can vary depending on the specific color and construction of the LED, but many standard LEDs operate effectively at around 2 to 3 volts.

Using direct current (DC) is crucial for LEDs, as they are designed to be used in a forward-biased configuration, meaning that current should flow in one direction—forward, from anode to cathode.

In contrast, the use of alternating current (AC) could result in sporadic illumination or potential damage because the alternating nature of AC could cause reverse voltage conditions that are harmful to the LED. Therefore, while 1.5 V AC and 5 V AC would not effectively light the LED, a voltage of 12 V DC would typically exceed the maximum forward voltage rating for most standard LEDs, risking overheating and failure.

The 3 V DC option provides sufficient and safe voltage to enable the LED to light up brightly without exceeding its voltage ratings, making it the appropriate choice for lighting an LED.