What is one common characteristic of light emitting diodes?

Light emitting diodes (LEDs) are semiconductor devices that emit light when an electric current passes through them. This phenomenon is known as electroluminescence. The key feature of LEDs is that they are diodes, which means they allow current to flow in one direction only. When current flows in the forward direction (from the anode to the cathode), it causes the electrons in the semiconductor material to recombine with holes, thereby releasing energy in the form of light.

This characteristic is crucial for their operation, differentiating them from other lighting technologies. LEDs can emit different colors of light depending on the materials used in their construction, but the defining feature remains their unidirectional current flow and the light emission that results from this.

The other options incorrectly represent the true characteristics of LEDs. While LEDs can emit various colors, including red, they are not limited to red light. Furthermore, they operate on direct current (DC) rather than alternating current (AC), and they do not require heat to function; rather, they are known for their efficiency and low heat output compared to incandescent bulbs.