Infrared light is outside of the visible spectrum of light that makes up all the colors we see. Usually, when you see a blue t-shirt, it's because that shirt is absorbing all the colors in the visible spectrum, but blue. Blue is being reflected and interpreted by our eyes, (basically).
Infrared light has similar properties, but what makes it so interesting and intriguing is the light is based on just purple (which is usually converted to black) and white. Foliage reflects all infrared light, so it ends up looking pure white. If an object has no infrared reflective properties, it just looks black. Normally you look at a tree and see green leaves, but with an infrared camera, the leaves are white, the trunk is black, the grass is white and a park bench would be black.
Traditional camera film is designed to capture visible light, but only works if the lens is open for a split second. Any longer and you over expose color and light to the film and nothing can be made of it. What is interesting, is that a fully exposed piece of film that has been processed (developed) will only allow infrared light to pass through it. So by using a digital camera that does not have an infrared blocker built in to the CCD, and removing the thin plastic enclosed blocker inside the camera in front of the CCD, we can insert a few layers of exposed film in front of the lens Egypt inside the camera). This will produce an infrared image on a digital camera, as seen in the photography on my website, linked below.