There’s a new streetlight in front of my house. It really isn’t hard to miss. I mean, they replaced those old sodium-burning lights for the harsh glow of the white LED’s.
It used to be that they would have to send energy into this little container of sodium, vaporizing the poor little container (hooray for anthropomorphizing atoms!) and turning it into a gaseous state. From there, the sodium was shot full of energy until those valence electrons began to jump, one by one, up the orbitals. Unfortunately, it doesn’t stay up there very long, and it crashes back to its original state in a fit of glory, releasing just one itty bitty photon along the way.