Mr. Pop, with my illuminator the 850 gives more glow. I did a little visual testing up to 100 yards with both 850 and 940nm, to determine if I could see a glow. The 850 could be seen all the way to 100 yards, though the glow was not intense. The 940 was seen out to about 70 yards or so. After that distance I could not see any glow at all. Just keep in mind to not stare at the light source if you conduct tests yourself. I would quickly glance at the source then shield my eyes. Those lights give off a tremendous amount of light that can be damaging if looked into them for any length of time.
One thing that surprises me however, is that my large 940nm spotlight that has 198 LED’s has no glow at all, even from 25 yards and closer. I have it mounted on a tall 4x4 post that is 25 yards from my coyote bait site. I deploy it remotely on and off when something is at the bait site, allowing me to look with both rifle scope and camera / monitor to determine what is there. It is pure stealth. I only wish my weapon mounted IR light was as stealthy.