Although there are many designs, the core of any optical spectrometer is some component that separates light by wavelength. Most commonly this component is a diffraction grating – a sheet of material etched with repeating grooves that causes light reflected from it or transmitted through it to diffract and bend at an angle proportional to its wavelength. Prisms – or some combination of gratings and prisms - can also be used to bend and separate light in this way. This bending and separation by wavelength is referred to as dispersion. If a camera is placed after the dispersive element, some geometry can be used to determine where on the camera different wavelengths will fall.