Light-emitting diodes shine in a spectrum of colors thanks to semiconductors inside them: materials that can easily shuffle electrons between two discrete energy levels when they’re connected to a power source. The color of an LED is directly connected to the gap between the semiconductor’s two energy levels. In this demo, YouTuber Tommy Technetium shows how that gap can change when an LED is dipped in –78 °C liquid nitrogen, changing a yellow LED to green. The low temperature increases the gap between semiconductors’ two energy levels. Specifically, it makes the lower energy level even lower and makes LEDs release higher energy photons, which are “bluer” than the room-temperature color.
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