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The US Army uses both Gen 2 and Gen 3 NVIS as goggles and weapon sights for ground operations. Because the peak sensitivity of Gen 2 goggles is in the visible green band, with relatively low sensitivity in the near-infrared (figure 15), they depend on lots of moonlight for best visibility.
Figure 15: Response of unfiltered Gen 2 and Gen 3 NVIS.
The best example of this NVIS type is the US Army's AN/PVS-5 (figure 16), the most common goggles for ground operations. The US Army also uses unfiltered Gen 3 NVIS, better suited to moonless conditions, when higher infrared (IR) sensitivity is preferable. The unfiltered Gen 3 response range still includes visible light down to 450 nm (figure 15). An example is the AN/PVS-7, available in Gen 2 and Gen 3 configurations. Known as "Cyclops," these goggles use only one intensifier tube to reduce cost (figure 17). NVIS for ground operations remains sensitive to any available nighttime radiation. NVIS for aviation takes a different approach and filters out most of the visible light to help avoid interference from crewstation light.
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