Hydrogen Lamp

Faint: the lamp's steady lines through the window. Bright: the lines sounding now, as strong as they are heard. Each line is one transition from a level n down to a level m, and sounds at its frequency over Hα's, (1/m² − 1/n²) ÷ (5/36); helium's over its yellow D₃ line's, from NIST's levels; molecular hydrogen's over its infrared 1–0 S(1) line's.

The levels of the atom (a Grotrian diagram), lit by how many atoms the lamps hold in each, with the lines heard drawn between the levels they join. An atom falls from level to level, l changing by one each time, until it reaches 1s; in slow motion you hear the cascade fill in after each key. Hydrogen's levels up to n = 7; helium's up to n = 5, the singlets and the triplets side by side (an atom hardly ever crosses between them), with the ground state 1¹S far below; molecular hydrogen's ground-state ladder of vibration (v) and rotation (J) below, and its excited electronic states far above.

Each line comes in as the cascade feeds its upper level and fades as the level empties after the key: the lines from high levels, fed only from above, light last. Their widths are the levels' lifetimes in slow motion, the atoms' Doppler shifts and the electric fields of the ions around them.