What is the primary function of a Light Emitting Diode (LED)?

The primary function of a Light Emitting Diode (LED) is to emit light only when current flows in the correct direction. LEDs are semiconductor devices that produce light through a process called electroluminescence. When an electric current passes through the LED in the forward direction, it energizes the electrons within the semiconductor material, causing them to emit photons, which we observe as light.

This characteristic of LEDs is crucial for their application in various devices, including displays, indicators, and lighting solutions. The requirement for current to flow in the correct direction (forward bias) ensures that LEDs operate effectively, distinguishing them from other components like regular diodes, which primarily allow current to pass in one direction but do not emit light.

The other options relate to functions not associated with LEDs. While sound generation is relevant to other components like buzzers, energy storage is typical of capacitors or batteries, and resistance to electrical flow pertains to resistors, these do not apply to the functioning of LEDs. Thus, option B accurately captures the essence of what an LED does.