Humans (and most animals) can see in the “dark” only if there is some starlight or, better, moonlight. It takes some time (10 to 30 minutes) for your eyes to become dark adapted to see in such low-light conditions. Best conditions are on a night with no clouds and a full moon (try it!). When dark adapted, you can see only in black and white (no color). If there is no light at all – say in a deep cave – you cannot see anything.
A few animals have infrared “vision”, which works by detecting heat. Heat produces infrared radiation, which is invisible to the human eye. In some snakes (for example, rattle snakes, that hunt mainly at night), this infrared vision is well developed. This vision only works when there is a temperature difference between objects, say between a warm blooded rodent and the background.
Night vision goggles allow to us see the infrared radiation with reasonable clarity, if there is a temperature difference between objects, but the sharpness of the view is not as high as with our usual daylight vision.
Infrared radiation and visible light are all part of the electromagnetic spectrum. They are waves of different frequency. Radio waves, microwaves, infrared and visible radiation, ultraviolet rays (which give sun burns) and X-rays are all part of that spectrum – each at different frequencies. These waves interact with matter (including us) in different ways depending on their frequencies.
Frank J. DiSalvo
Ph.D. Stanford University
Wife, Barbara, 2 Daughters, 4 grandchildren
Fishing, swimming, traveling
West Middle School Science Club
West Middle School