|Does red or blue light bend more in glass?
Blue light almost always bends more than red light because blue light almost always travels more slowly through glass than does red light. This phenomenon is known as dispersion However, there are some glasses that exhibit anomalous dispersion, where red light travels faster and bends more than blue light. Anomalous dispersion only occurs when there is a resonant absorption of light in the glass, typically because of some impurity atoms or ions in the glass or because of some transition that occurs in the glass itself. While the resonance will only absorb light at one particular wavelength, it alters the propagation of light at nearby wavelengths. At wavelengths just shorter than the absorbed wavelength, light travels anomalously fast through the glass so that it bends less than light that is somewhat redder in color.