Paschen series
(hydrogen lines for electrons settling from n > 3 to n = 3)
The Paschen series is the set of
emission lines from atomic hydrogen gas,
due to electrons descending from
an electron shell number n greater than 3 down to n = 3,
or the analogous absorption lines when absorbed electromagnetic radiation
makes electrons do the opposite.
It is one of the hydrogen line series, such as
the Lyman series and Balmer series and is
named after Friedrich Paschen.
Lines:
 4 > 3: 1875 nm
 5 > 3: 1282 nm
 6 > 3: 1094 nm
 7 > 3: 1009 nm
 8 > 3: 995 nm
 9 > 3: 887 nm
 ...
 infinity > 3: 820 nm
Formula for wavelengths:
1/wavelength = R_{H} ( 1/9  1/n² )
 wavelength is the wavelength within the Paschen series.
 R_{H} is the Rydberg constant for hydrogen, 1.0973731568160 × 10^{7}m^{1} = 13.6 eV / hc
 n is the higher electron shell number.
 h  Planck constant.
 c  speed of light in a vacuum.
(Paschen,hydrogen,line series,lines,spectrum)
Further reading:
http://en.wikipedia.org/wiki/Hydrogen_spectral_series
WaveL  Freq  Photon Energy   
820nm  366THz  1.6eV  begin  Paschen series 
1875nm  160THz  661meV  end  Paschen series 

Referenced by pages:
hydrogen (H)
spectral line
Index