Contact lens converts IR to visible light. Use cases include night vision and seeing if your tv remote is working.

Seems like it would be good for marking cards. Make some cards reflect in the NIR. These contacts don't focus, however, so you can't get a clear perception of where the NIR is coming from.

TL;DR You can see heat, and normally invisible IR signalling so you can see your universal TV remote light up and other things, potentially air or liquid currents as turbulent flow, when its sensitive enough (which it isn't at this point).

The downsides they seem to ignore, include the literature showing light on the lower end Blue->UV, and light on the upper end to NIR, have direct impact on the endocrine system through light activated pathways in your eye. If you wear a contact lens, this light is blocked, the same goes for laser eye surgery where a artificial lens is used.

John Ott, and Fritz Hollwich pioneered early studies on photobiology, and funding for it has been sparse despite Asia's myopia crisis; which statistics show generally increased dramatically shortly after blue LEDs came to market in the late 90s, and appear correlated with exposure.