The electrons travel through the tube, accelerating towards anotherplate and causing a cascade effect that increases the number ofelectrons. These electrons strike a screen coated with aphosphorescent compound that will glow as shown in Figure 2-3.When using an I2 NVD, the operator views the scene through anocular lens that focuses the image. A separation between the ocularlens and the eye, known as eye relief distance, is necessary.Many types of phosphor screens are available on I2 devices, with themost common being designated P22 (green), P43 (yellow-green), andP45 (white). The P22 screen is the most commonly used, and is the popular choice for militaryand law enforcement due to the wider visible spectrum. The P43 screen has a narrower visiblespectrum and has become popular among aviators for its fast decay time (i.e., the time it takes forthe image to fade on the screen). The P45 screen provides similar decay times to P43, withexcellent recognition capability. The image presented to the user of a P45 screen is black andwhite, which results in less eye fatigue, faster recognition (especially in sandy/rocky terrain), anda slightly better discrimination of shades of intensity than the traditional green