A diode is a device that typically allows current to pass in one direction only. The die, or semiconductor portion of an LED is doped in such a way that it will emit photons when current is passed through it in a forward direction, but does nothing when current is applied in the opposite direction. GaN, GaP, and GaAsP are normal materials that modern LEDS are made out of, although things like Silicon Carbide were used for the old green and yellow LEDS of the past. These were so inefficient that they were quickly replaced by other technolgies. LEDs didn't really get bright enough to do anything other than be a weak indicator until the 80s when brighter LEDs showed up on the market for a reasonable price, regardless of what people think were in their car instrument panels or electronics at the time. LEDs were discoveredaround 1907, as Silicon Carbide crystals will emit very weak light when a current is applied. These were so inefficient and random that it wasn't until the 60s that LEDs as we know them became a thing. ( https://en.wikipedia.org/wiki/H._J._Round ) TL;DR, A LED is a diode (one-way device) that emits light when powered, therefore an LED.