Visible light and infrared radiation are both forms of electromagnetic radiation, differing primarily in terms of their wavelength and the corresponding energy they possess.
Visible light is the portion of the electromagnetic spectrum that can be detected by the human eye. It consists of various colors ranging from violet (shorter wavelength, higher energy) to red (longer wavelength, lower energy). The visible light spectrum spans approximately 400 to 700 nanometers (nm).
Infrared radiation, on the other hand, has a longer wavelength than visible light, falling just beyond the red end of the visible spectrum. It extends from around 700 nm to 1 millimeter (mm) in wavelength. Infrared radiation is often divided into three regions: near-infrared (NIR), mid-infrared (MIR), and far-infrared (FIR), based on their respective wavelength ranges.
The main difference between visible light and infrared radiation lies in their interaction with matter and their detection by different technologies:
Detection: Visible light can be detected by the human eye, which contains specialized cells (rods and cones) that respond to different wavelengths of light. In contrast, infrared radiation is invisible to the human eye. It requires specialized detectors such as infrared cameras or sensors to be observed and measured.
Energy: Visible light carries higher energy compared to infrared radiation. This difference in energy is responsible for the human eye's ability to perceive visible light as colors, whereas infrared radiation is felt as heat.
Penetration: Visible light interacts with matter in various ways. It can be reflected, transmitted, or absorbed depending on the properties of the material. Infrared radiation, particularly in the NIR and MIR regions, has the ability to penetrate certain materials, such as glass or plastic, to a certain extent. Far-infrared radiation (FIR) has even greater penetration capabilities and can be used to study the internal structure of materials or for thermal imaging.
Applications: Visible light is essential for human vision and is used extensively in lighting, photography, and displays. Infrared radiation, due to its ability to detect heat signatures and penetrate certain materials, finds applications in night vision devices, thermal imaging cameras, remote sensing, medical imaging (such as infrared thermography or infrared spectroscopy), and even in some cooking appliances.
Despite these differences, both visible light and infrared radiation are part of the broader electromagnetic spectrum and share fundamental properties like the ability to propagate through vacuum, exhibit wave-particle duality, and travel at the speed of light.