[micheljansen]

A cool property of NIR filters is that they are able to produce a relatively recognisable picture of the world with all screens (TFT, projected) filtered out. I've used this in the past for computer vision to do object recognition on top of a projected display without having to programmatically filter out the projection.

It's also pretty easy to make a rudimentary NIR filter by layering a red, green and blue filter on top of each other: the resulting filter will not allow any visible light through (e.g. red, green or blue), only the "rest".

edit: and they make your eyes look really creepy too (not me in the picture btw): https://flic.kr/p/6CYzDZ

[Artlav]

Another easy way to make a NIR filter is to get a couple of black frames of a regular photographic film - it's transparent to NIR, but blocks all the visible light.