The human eye allows us to perceive the world around us through light. However, our visual capabilities are not limitless. We detect only a small fraction of the entire electromagnetic spectrum, leaving a vast range of ‘colors’ and light types invisible to us.
The Visible Spectrum
The visible spectrum is the range of electromagnetic radiation the human eye can detect, typically spanning 380 to 750 nanometers (nm). Within this narrow band, our brains interpret different wavelengths as distinct colors, forming the familiar rainbow of red, orange, yellow, green, blue, indigo, and violet (ROYGBIV). Red light has the longest wavelength, while violet has the shortest.
Beyond the Visible Range
The visible spectrum is only a small portion of the larger electromagnetic spectrum. Beyond violet lies ultraviolet (UV) light (10-400 nm), and past red is infrared (IR) light (700 nm-1 millimeter). Our eyes lack the photoreceptors to translate these wavelengths into perceived color, making them invisible to most humans. The electromagnetic spectrum also includes radio waves, microwaves, X-rays, and gamma rays. These are not considered ‘colors’ and exist far outside our visual system’s processing range.
The Biological Basis of Human Vision
The reason human eyes are limited to the visible spectrum lies within their biological structure, specifically the retina. The retina contains specialized cells called photoreceptors: rods and cones. Rods are sensitive to low light, providing black and white vision. Cones are responsible for color vision and require more light.
Humans possess three types of cones, each sensitive to different wavelengths: short (blue), medium (green), and long (red). These cones detect specific light wavelengths, sending signals to the brain for color interpretation. Our eyes lack photoreceptors tuned to wavelengths outside the 380-750 nm visible range, like UV or IR light. The lens also filters out most UV light, protecting the retina.
How Other Animals Perceive Light
While humans are limited to the visible spectrum, many animals have evolved different visual systems to perceive light beyond our capabilities. Insects like bees and butterflies see ultraviolet (UV) light, using it to identify flower patterns for nectar. Birds, such as starlings, also possess UV vision, with some female birds’ feathers reflecting UV light to attract mates.
Other animals perceive infrared (IR) light. Pit vipers, boas, and pythons use specialized pit organs to detect IR radiation, sensing prey heat in the dark. Some fish, like goldfish and salmon, have enzymes enabling IR vision for navigation and hunting.
Goldfish are unique, believed to see both IR and UV light. Mantis shrimp have up to 16 types of photoreceptors, detecting both ultraviolet and polarized light. This diversity highlights how life adapts to interpret the vast electromagnetic spectrum.