Although the human eye is sensitive to a specific range of wavelengths known as the visible spectrum, it is still possible to perceive objects that emit or reflect light outside of this range. There are a few reasons for this:
Sensitivity of detectors: While the human eye has its peak sensitivity in the visible range (approximately 400-700 nanometers), it is not completely insensitive to light outside of this range. The sensitivity of the eye gradually decreases as we move away from the visible spectrum, but it can still detect certain wavelengths of light to some extent. For example, some people may perceive faint flashes of ultraviolet (UV) light or longer-wavelength light in the near-infrared (NIR) range.
Interaction with visible light: Objects that emit or reflect light outside of the visible spectrum may still interact with visible light in a way that is detectable to our eyes. For instance, certain UV-emitting objects can cause fluorescence in nearby materials that emit visible light when excited by UV radiation. This fluorescence can then be observed by the human eye.
Converting light to visible range: In some cases, special optical devices or materials can be used to convert light of non-visible wavelengths to the visible range. For instance, certain imaging techniques, such as thermal imaging or night vision, employ technology that detects and converts infrared (IR) radiation into visible images that can be seen by humans.
It's important to note that the ability to perceive objects outside the visible spectrum is limited and depends on various factors, including the intensity of the non-visible light, individual variations in human vision, and the use of technological aids. In general, the visible spectrum represents the range of light that our eyes are most sensitive to, and objects emitting or reflecting light outside of this range may not be perceived in the same way as those within the visible spectrum.