= Balmer series
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The <Balmer series> consists of hydrogen transitions terminating at <principal quantum number> $n=2$. Its emission wavelengths obey $1/\lambda=R_H(1/4-1/n_i^2)$ for $n_i=3,4,\ldots$, a special case of the <Rydberg formula>.
The first transitions fall in the visible part of the <electromagnetic spectrum>, while the high-level lines converge toward a shorter-wavelength limit with $\lambda_{\rm lim}=4/R_H$. A hydrogen discharge observed through a <spectroscope> shows separated lines rather than a smooth continuum because the atomic energy differences are discrete.
The same level separations can produce absorption when atoms initially occupy the lower state. Temperature, excitation and the number of atoms in that state affect line strength; a wavelength formula alone does not predict the observed relative intensities.
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