What is a sign of failing image intensification in NVG units?

In night vision goggles, failing image intensification can lead to several observable issues, one of which is edge glow. This phenomenon occurs when bright light sources cause a noticeable halo or brightening at the edges of objects in the NVG's field of view. This can detract from the clarity of the image and indicate a degradation in the performance of the image intensifier tube. Edge glow is a common symptom that signifies that the NVG units may be nearing the end of their operational lifespan or that they may require servicing.

Constant clarity and reduced weight are not indicators of any failure in image intensification. Constant clarity suggests that the NVGs are functioning well, while reduced weight relates more to design and materials used in manufacturing, not the performance of the image intensifier. The choice of "None of the above" would imply that no signs of NVG failure have been listed, which is incorrect since edge glow is indeed a well-documented symptom of failing image intensification.