Visible light consists of a spectrum of colors (ROY G. BIV, et. al.), and there are a set of invisible light waves on either side of visible, called ultraviolet on the blue side and infrared on the red side. Humans can't see them, but some animals and insects can. For instance, flowers which are uniformly colored in the visible have clear ultraviolet patterns to direct insetts to optimal pollination. There is generally a lot more of a spectrum of near infrared light than there is of visible light, and digital cameras are sensitive to this light and can "see" this to some extent, and show it as some form of reddish, whitish, or bluish image because the software of the camera doesn't know what to do with the stimulation that it's sensors are getting, and just interprets it as best it can. The stimulation the camera receives is mostly from infrared light close to the visible spectrum, hence it is often called NIR or Near InfraRed. Far infrared is things like heat, which is a form of radiation much longer in wavelength than NIR or visible and is typically used for those "night vision" goggles. Digicameras aren't sensitive to this. Most things are colored to some extent in the infrared, that is, they absorb or reflect light to different extents. Living trees reflect brightly, dead ones not so much. Eyes often look dark and translucent because NIR passes through the white part. Fair skin is often translucent and veins/capillaries can appear. (this may be, too, I think, why biting insects can see where to pierce the skin). Images that are camouflaged by surrounding color can often suddenly be contrasted.
You can back journey in my journal, or you can visit sites like http://www.irdreams.com/
(some not work-safe images) to see what potential seeing light that isn't visible can do for photography. For a more scientific and work-safe reason, there are sites like http://www.naturfotograf.com/index2.html
There are no stupid questions. My goals in life center around challenging and questioning reality and coming to think clearly and correctly. I'm Matt, and I'm a twisted boy. I hope you enjoy reading. lapis_lazuli
recommended that I read your journal.