The PARISS® Micro-Spectrophotometer A Comparison of Prism Versus Diffraction Grating Efficiency Light throughput (efficiency) compared • Prism: close to 100% from ~390 to ~1000 nm.  • Diffraction grating: Varies across the spectrum. Maximum efficiency is at a single “blaze”: wavelength High order diffraction • Prism: NONE all wavelengths are refracted to the detector • Diffraction grating: can present many orders Benefit: A prism is significantly more sensitive than a diffraction grating over an extended wavelength range. Camera quantum efficiency (QE) versus spectral resolution • The QE of a CCD camera falls at longer wavelengths • The spectral resolution of a prism also falls at longer wavelengths.  However, this is a good thing!. Benefit: A prism effectively compensates for the loss in the QE of the camera. The net result is enhanced light throughput extending into the near IR exceeding that possible with a diffraction grating  View this movie to see how diffraction gratings produce higher orders.  The presence of higher orders dilutes light in first order where the detector is located  Copyright © LightForm Inc, 2011