Because the red color in the visible spectrum has a higher wavelength than most other colors, this effect is also commonly called a red shift, although this usage is considered informal, and has no relation to Doppler shift or other wavelength-independent meanings of redshift. This usage is often found in the scientific literature.
This 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
See also 
- Hypsochromic shift, a change to shorter wavelength (higher frequency)