Infrared rays are a form of electromagnetic radiation whose wavelengths lie between 750 nanometres and 1 millimetre. These wavelengths lie between visible light and microwave radiation, just beyond the spectrum of red light. Because the wavelength of infrared radiation is just a bit longer than the wavelengths that the eye can perceive, infrared radiation is invisible to the human eye. However, you can sense IR radiation with your skin, which perceives it as heat.
Materials that Absorb IR Wavelengths.
Most materials absorb some IR wavelengths although it may be only a small per cent. Others, such as water vapour in the Earth's atmosphere absorbs the majority of the IR radiation that comes from the sun. In addition, carbon dioxide, ozone and oxygen also absorb much of the IR radiation, allowing very little to actually reach the ground. Aside from water vapour, bodies of water on the surface of the Earth also absorb IR wavelengths well. Glass, Plexiglas, wood, brick, stone, asphalt and paper all absorb IR radiation. While regular silver-backed mirrors reflect visible light waves, allowing you to see your reflection, they absorb infrared radiation. Gold, manganese and copper also absorb IR radiation well. According to Next Energy News, the U.S. Department of Energy is using these three metals to design nanoantennas, which will convert waste heat in the form of IR radiation into electricity.
Materials that Reflect IR Radiation
Skin reflects IR radiation, as does aluminium foil. Because of aluminium foil's IR reflection ability, placing sheets of aluminium foil behind your radiator on an exterior wall can reduce heat loss through the wall. Snow's ability to reflect IR radiation back into space helps to keep the planet cooler. If your car sits in the sun too long, it becomes too warm inside. Partly this is from trapping visible light waves, but a bigger effect is the absorption of IR radiation by the car's paint.
Materials that Radiate IR Radiation
Almost everything in the universe radiates IR wavelengths unless it is at minus 460 degrees Fahrenheit, which is absolute zero and is the coldest possible temperature. At this temperature, the bonds in a molecule stop rotating and it has no more energy to radiate as heat. Interestingly, materials that are good at absorbing infrared radiation are also good at emitting, or radiating, that radiation. Even glaciers emit IR radiation although at much lower levels than water. Incandescent light bulbs emit a lot of IR radiation along with visible light, whereas the newer fluorescent bulbs do not.
Colour of Materials
Darker colours absorb the visible wavelengths in sunlight, not IR rays. Therefore, the colour of the material is unimportant in the ability of a material to absorb infrared light. That may change, however, with the development of new technologies. According to Plastemart, new pigments designed to reflect IR radiation will soon keep the car interior cooler.