I took this pic this morning showing something green in the frame
ISO 1600 30 second exposure f/5.6 70-300mm @300mm
It is right under the camera lens and i turned it on and off a couple of times, but i would think that it will ruin an image even at a distance if it crosses the imaging path enough times or stays within it for long enough.
So it definately shows up and would be a problem if people are waving these things around all over the place while others are trying to image.