Night Optics Falcon 6x Gen 3 Gated Long-Range Night Vision Binocular - Manual (Page 63)

2-28
b. Operational Defects. These defects relate to the reliability of
the image intensifier and are an indication of instability. If
identified, they are an immediate cause for rejecting the NVG.
They include shading, edge glow, flashing, flickering, and
intermittent operation.
(1) Shading. If shading is present, you will not see a fully
circular image (see Figure 2-3). Shading is very dark and you
cannot see an image through it. Shading always begins on the
edge and migrates inward eventually across the entire image area.
Shading is a high contrast area with a distinct line of demarcation.
Return the NVG to the maintainer.
Figure 2-3. Shading.