There seems to be many who say you can't see IR ... Wrong. The fact that I can, is causing me a problem. I work in the security field, ultra low light video camera's, IR illuminators etc, most of these have to be totally Covert, with respect to the IR spotlights.
Currently using Osram SFH 4503 IR leds, which have a peak wavelength @950nm, a half angle of +/-4 degrees, spectral bandwidth of 40nm and a radiant intensity of 250mW/sr. These are really bright. There is about 10% of this bandwidth at 875nm, tailing off to about 1% at 850nm, so basically nothing below 845nm. With a 12x led spot, using these leds, in total darkness, and viewed, on-axis, these are Very easy to see, not covert at all. Ok, we're possibly only seeing the 850nm end, but is seen as quite bright due to the 8 degree beam angle and the high power of these leds.

So as to humans 'Not' seeing IR, I would have to disaggree, it's all down to relative intensity, eye colour seems to be relevant too, if the IR is very powerful, the eye will catch some of this.

Steve