A diode is an electrical component with the fundamental property of only allowing electric current to flow in one direction through it. This property is essential to the conversion of alternating current into direct current, which is why diodes are commonly found in AC adapters and other rectifier circuits. The most common type of diode nowadays is the semiconductor diode (see Figure 1).
Additionally, diodes can give off light, and these are called light emitting diodes, or LEDs. Commercial LED light bulbs have been available since the 1960s, but technical developments and improvements in the 1990s and 2000s greatly boosted their popularity. This product helps reduce energy consumption, and avoids the mercury contamination of compact florescent bulbs. Another key advantage is that LEDs almost never burn out the way traditional light bulbs do. The physics of these diodes are quite closely related to photovoltaic cells. LEDs take electricity and make light, while photovoltaic cells take light and make electricity.
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