That doesn't look like it's affected by amp noise, so probably no effect at all. What Long Exp NR does is to eliminate the pinkish blobs that sometimes seem to intrude on the edges of frames with long exposures. It's caused by thermal buildup on electronic components near the sensor, so the various cameras have different liabilities in this regard. (Presumably also the various sensors affect this too.)
The way it works is to take your exposure, then leave the shutter closed and captures another one that should be all blank. If amp noise is affecting the sensor, the camera can safely conclude that anything in the blank exposure should not be, and it subtracts that from your exposure before it saves it to flash memory.
_____ Brian... a bicoastal Nikonian and Team Member
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