Introduction
The rainbow, a natural spectrum of light in the sky, has long fascinated humans. Commonly described through the acronym ROYGBIV, it represents the colors Red, Orange, Yellow, Green, Blue, Indigo, and Violet. However, this visible spectrum is just a part of the electromagnetic spectrum that includes wavelengths not visible to the human eye, such as ultraviolet (UV) and infrared (IR).
The Visible Spectrum
The visible spectrum comprises wavelengths of light that the human eye can detect, approximately ranging from 380 to 750 nanometers (nm). This range encompasses all the colors we traditionally associate with a rainbow. The perception of these colors results from the varying wavelengths of light, with red having the longest wavelength and violet the shortest in the visible range.
Beyond the Visible: Ultraviolet
Ultraviolet light lies just beyond the violet end of the visible spectrum, with wavelengths ranging from 10 to 400 nm. It’s not visible to the human eye due to its shorter wavelength and higher energy than violet light. However, some animals, like bees, can see ultraviolet light, which aids them in pollination.
UV light is typically divided into three categories:
- UVA (315 to 400 nm): The least harmful and most commonly experienced type of UV radiation.
- UVB (280 to 315 nm): More harmful and responsible for sunburns.
- UVC (100 to 280 nm): The most harmful but completely absorbed by the Earth’s atmosphere.
Infrared: The Heat Beyond Red
Infrared light exists just beyond the red part of the visible spectrum, with wavelengths from about 750 nm to 1 mm. Infrared is typically divided into:
- Near-infrared (750 nm to 1.4 µm): Closest to visible light and used in remote controls and night-vision equipment.
- Mid-infrared (1.4 to 3 µm): Used in thermal imaging.
- Far-infrared (3 µm to 1 mm): Felt as heat and used in heaters and thermal cameras.
Scientific Applications
Both UV and IR light have significant applications in science and technology. UV light is used in sterilization and forensic analysis, while infrared technology is critical in weather forecasting, astronomy, and medical diagnostics. While the human eye perceives a rainbow as consisting of seven distinct colors, the electromagnetic spectrum extends well beyond this range. Ultraviolet and infrared light represent the invisible parts of a rainbow, each with unique properties and applications. Understanding these invisible wavelengths opens up a world of scientific and technological possibilities, from medical advancements to deepening our understanding of the universe.