 A different sort of spectrometer component called an immersed grating also consists of a prism with a diffraction grating ruled on one surface.However, in this case the grating is used in reflection, with light hitting the grating from "inside" the prism before being totally internally reflected back into the prism (and leaving from a different face).The reduction of the light's wavelength inside the prism results in an increase of the resulting spectral resolution by the ratio of the prism's refractive index to that of air.