Editing Light-emitting diode (section)

=== Power sources ===
{{Main|LED power sources}}
[[File:LED circuit.svg|class=skin-invert-image|thumb|upright|Simple LED circuit with resistor for current limiting]]

The current in an LED or other diodes rises exponentially with the applied voltage (see [[Shockley diode equation]]), so a small change in voltage can cause a large change in current. Current through the LED must be regulated by an external circuit such as a [[constant current]] source to prevent damage. Since most common power supplies are (nearly) constant-voltage sources, LED fixtures must include a power converter, or at least a current-limiting resistor. In some applications, the internal resistance of small batteries is sufficient to keep current within the LED rating.{{citation needed|date=October 2020}}

LEDs are sensitive to voltage. They must be supplied with a voltage above their [[P–n junction#Forward bias|threshold voltage]] and a current below their rating. Current and lifetime change greatly with a small change in applied voltage. They thus require a current-regulated supply (usually just a series resistor for indicator LEDs).<ref>[http://www.ledmuseum.org/ The LED Museum]. Retrieved on March 16, 2012.</ref>

[[LED droop|Efficiency droop]]: The efficiency of LEDs decreases as the [[electric current]] increases. Heating also increases with higher currents, which compromises LED lifetime. These effects put practical limits on the current through an LED in high power applications.<ref name="stevenson">Stevenson, Richard (August 2009), "{{usurped|1=[https://web.archive.org/web/20090805082614/http://www.spectrum.ieee.org/semiconductors/optoelectronics/the-leds-dark-secret The LED's Dark Secret: Solid-state lighting will not supplant the lightbulb until it can overcome the mysterious malady known as droop]}}". ''IEEE Spectrum''.</ref>