Paschen Series
The spectral series of hydrogen atom emission lines produced by electron transitions dropping from upper energy states to the n=3 level.
Governing formula
1 / λ = R_H (1 / 3² - 1 / n_i²), n_i = 4, 5, 6...
SI unit
Infrared Wavelengths (nm)
In depth
Because energy drops to the n=3 shell are smaller, Paschen series emissions fall entirely within the infrared spectrum. They are undetectable by the human eye but measurable using infrared detectors.
Examples in the real world
Infrared astronomical observations studying cool interstellar gas clouds where visible Balmer light is obscured by cosmic dust.