It can occur because of a change in environmental conditions: for example, a change in solvent polarity will result in solvatochromism.
A series of structurally-related molecules in a substitution series can also show a bathochromic shift. Bathochromic shift is a phenomenon seen in molecular spectra, not atomic spectra; it is thus more common to speak of the movement of the peaks in the spectrum rather than lines.
where  is the wavelength of the spectral peak of interest and