When we say that we cannot "see" infrared or ultraviolet light with our eyes, it means that our eyes are not naturally sensitive to these specific wavelengths of light. The human visual system is designed to detect and perceive a narrow range of light wavelengths known as the visible spectrum, which spans from approximately 400 to 700 nanometers (nm).
Infrared (IR) light has longer wavelengths than those within the visible spectrum, ranging from about 700 nm to 1 millimeter. Ultraviolet (UV) light, on the other hand, has shorter wavelengths than those within the visible spectrum, ranging from about 10 to 400 nm. While both infrared and ultraviolet light exist in the environment and can reach our eyes, our eyes are not equipped to directly perceive or interpret these wavelengths.
However, even though we cannot see infrared or ultraviolet light, their waves can still enter our eyes and interact with the structures within. For instance, infrared light can pass through the various layers of the eye, reaching the retina. Certain specialized devices, such as infrared cameras or sensors, can detect and convert infrared light into a visible image that we can interpret.
Ultraviolet light, especially in high doses, can have harmful effects on the eyes and the skin. The cornea and lens of the eye offer some natural protection against UV light, but excessive exposure can lead to issues like sunburned eyes (photokeratitis), cataracts, or other eye damage. It is crucial to take precautions, such as wearing UV-blocking sunglasses or using appropriate protective eyewear, to safeguard the eyes from excessive UV exposure.
In summary, while infrared and ultraviolet light can enter our eyes, our visual system is not naturally sensitive to these wavelengths, and we cannot perceive them as visible light.