How Does Light Interact With Matter?

The interaction of light with matter varies based on the type of matter, the geometry of matter, the wavelength of the incident light and the light intensity. Because different parts of the electromagnetic spectrum interact differently with the same form of matter, there is no one specific interaction between light and matter.

Taking the human body as an example of matter, low frequency electromagnetic waves, such as radio waves, pass through the body with almost no interaction. The transparency of radio waves to most forms of matter makes it possible to receive radio waves even when a radio receiver is not in direct line of sight of the emitting radio tower. As the frequency of the electromagnetic waves gets higher, the wavelength gets shorter.

Microwaves, infrared waves and visible light are all well absorbed by the matter of the human body. Microwaves are particularly dangerous in the sub-visible region of the electromagnetic spectrum, because they are still of a low enough frequency to penetrate through the body, but high enough in energy to excite water molecules to boiling by matching the resonant frequency of these molecules. The post-visible range of the electromagnetic spectrum includes short wavelength, high-energy radiation, such as ultraviolet, x-ray and gamma radiation, that causes permanent damage to bodily tissues in even small doses.