The Secondary Electron Detector (SED) is the first link in the chain of image formation after the initial illumination of a specimen in a Scanning Electron Microscope (SEM), therefore it is most crucial that the efficiency of the SED be as great as possible in order to maximize Signal-to- Noise Ratio (S/N) as any imperfections, inadequacies, and noise are then amplified along with the signal by the subsequent electronic amplifiers in the signal chain.

In the Everhart-Thornley SED, matching the scintillator's output spectrum to the photomultiplier tube's photocathode spectral sensitivity is one factor along with other characteristics of the PM tube, like quantum efficiency and noise characteristics. Light-pipe material along with as optical coupling techniques are another factor which determines the overall efficiency of converting SE electron strikes on the scintillator to a video output signal.