Infrared light is located or can be found between the visible and microwave portions of the electromagnetic spectrum. Infrared light has a range of wavelengths, just like visible light has wavelengths that range from red light to violet. "Near infrared" light is closest in wavelength to visible light and "far infrared" is closer to the microwave region of the electromagnetic spectrum.

Far infrared wavelengths are about the size of a pin head and the shorter, near infrared ones are the size of cells or basically microscopic.

Source of Infrared Radiation

The primary source of infrared radiation is heat or thermal radiation, any object which has a temperature radiates in the infrared. Even objects that we think of as being very cold, such as an ice cube, emit infrared energy.

When an object is not quite hot enough to radiate visible light, it will emit most of its energy in the infrared form. For example, hot charcoal may not give off light but it does emit infrared radiation which we feel as heat.

The warmer the object, the more infrared radiation it emits.

Our Body and Infrared radiation

Our body at normal temperature radiate most strongly in the infrared at a wavelength of about 10 microns. (A micron is the term commonly used in astronomy for a micrometer or one millionth of a meter.) Many things besides human body and animals emit infrared radiation – for example the Earth, the Sun, and even far away things like stars and galaxies also emit infrared radiation.