Emission spectrum: 1/lambda = $RZ^2$(1/$n1^2$ - 1/$n2^2$), R = 1.097 x 10^7 $m^{-1}$. Series: Lyman (n1=1, UV), Balmer (n1=2, visible), Paschen (n1=3, IR), Brackett (n1=4, IR), Pfund (n1=5, far IR). For each series: first line has n2 = n1 + 1 (longest wavelength, lowest energy). Series limit has n2 = infinity (shortest wavelength, highest energy). Total lines when electron falls from n to ground state: n$\frac{n-1}{2}$. Lines in a specific series from level n to n1: n - n1 lines. Balmer series visible lines: H-alpha (656 nm, red), H-beta (486 nm, blue-green), H-gamma (434 nm, violet), H-delta (410 nm, violet). The hydrogen spectrum was the first evidence for quantised energy levels.