In spectroscopy, bathochromic shift (from Greek βαθύς (bathys) 'deep' and χρῶμα (chrōma) 'color'; hence less common alternate spelling "bathychromic") is a change of spectral band position in the absorption, reflectance, transmittance, or emission spectrum of a molecule to a longer wavelength (lower frequency).
[1] Because the red color in the visible spectrum has a longer wavelength than most other colors, the effect is also commonly called a red shift.
Hypsochromic shift is a change to shorter wavelength (higher frequency).
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.
Bathochromic shift is typically demonstrated using a spectrophotometer, colorimeter, or spectroradiometer.