Infrared

Infrared, like ultraviolet at the other end, is invisible to the human eye: it is electromagnetic radiation of longer wavelength than red, discovered by William Herschel in 1800 when he measured a rise in temperature just beyond the red edge of a spectrum cast by a prism and realised there were rays there that carried heat but no light. Everything warm radiates in the infrared, which is why thermal cameras can see in the dark.

In modern esoteric colour systems infrared serves as the band below the root, the invisible red-ward extension of the chakra rainbow, associated with the densest, most physical and instinctual level, the body's survival heat beneath the visible spectrum of the subtle centres. As with ultraviolet above the crown, this is a twentieth-century analogical use rather than any traditional attribution; the older chakra sources know nothing of infrared, and the extension of the visible rainbow into the invisible bands is a recent feature of aura and energy literature. Physically, infrared is simply radiant heat.

Infrared is radiation beyond the red end of the visible spectrum, and its discovery in 1800 is the moment the idea of light stopped being coextensive with the idea of colour.

William Herschel was looking for a practical answer to a practical problem: which coloured filter would let him observe the sun without burning his eye. He passed sunlight through a prism and moved a thermometer along the spectrum to see which colours carried the most heat. The reading rose from violet toward red, and then, when he moved the bulb past red into what appeared to be nothing at all, it rose further still. He had measured radiation outside the visible band, and he called it radiant heat.

The consequence for colour symbolism is the same as for ultraviolet at the other end, and it should be stated as plainly. Infrared has no traditional correspondences because no tradition could perceive it. Any scheme that assigns it a planet, a chakra or a virtue is a modern construction extending an older system into territory that system never covered, and the atlas records it as such.

What infrared does have is a substantial modern life. Thermal imaging reveals heat rather than light, and it is used in astronomy to see through the dust that blocks visible wavelengths, so a good deal of what is now known about star formation was obtained in a band nobody can look at. Some snakes detect infrared through pit organs, which is a form of sight that has nothing to do with eyes.