Infrared radiation and visible red light differ primarily in terms of their wavelengths and how they interact with matter.
Visible light is a narrow range of electromagnetic radiation that humans can perceive with their eyes. It spans a wavelength range of approximately 400 to 700 nanometers (nm). Within the visible spectrum, red light has longer wavelengths and is typically perceived as light with a wavelength of around 620 to 750 nm.
Infrared (IR) radiation, on the other hand, has longer wavelengths than visible light. It occupies the region of the electromagnetic spectrum just beyond the red end of the visible spectrum. Infrared radiation spans wavelengths ranging from about 700 nm to 1 millimeter (mm), although the boundaries of the IR region can vary in different contexts.
The longer wavelengths of infrared radiation have several implications:
Perception: Infrared radiation is not visible to the human eye. We cannot directly perceive it as light, unlike visible red light.
Interaction with matter: Infrared radiation interacts differently with matter compared to visible light. While visible light is readily absorbed and reflected by many objects, infrared radiation can pass through certain materials, including some types of glass, plastics, and fabrics.
Heat transfer: Infrared radiation is strongly associated with heat. Objects at normal temperatures emit infrared radiation, which we commonly refer to as thermal radiation. Infrared radiation is often used to measure or detect temperature variations, as it can indicate the thermal energy emitted or absorbed by objects.
In summary, infrared radiation has longer wavelengths than visible red light, making it invisible to the human eye. It interacts differently with matter, and its association with heat makes it valuable for various applications related to temperature sensing and thermal imaging.