This is quite an interesting article on building a pair of cheap infrared goggles and how they work.
At one point I started wondering just how much IR light a human eye could see. After all, if the infrared light was EXTREMELY BRIGHT (such as the IR of a sunny day,) human eyes might still detect it. And remember, if 30KHz ultrasonic sound is loud enough, you will hear it. Same basic idea. I got some of our black IR filter plastic and cut it into 2in. oblong disks to fit the eye-depressions in my own skull. I taped them onto my face with black electrical tape. Yes, I looked odd, but it worked! After I became accustomed to the darkness inside the filters, I could see through them. Going outside on a sunny day was stunning. The sky was almost black, while the trees and shrubs where all frosty pink. The grass looked like fluorescent red cherry Koolaid powder. Different colors of human skin were always the same light grey. People’s eyes looked very black, and certain dark clothing looked white. I was afraid that I might damage my eyes, since the IR sunlight was very bright, and my pupils were wide open. (After years of playing with these, I still haven’t hurt my eyes, so they’re PROBABLY somewhat safe to use.)