Light allows us to perceive the world’s colors. What precisely gives light its color? Understanding this requires exploring the physical nature of light itself.
Light as a Wave
Light travels through space as an electromagnetic wave. Like other waves, it has wavelength (the distance between two consecutive peaks or troughs), frequency (the number of wave cycles passing a fixed point per unit time, typically measured in hertz), and amplitude (the wave’s height, indicating brightness). Wavelength and frequency are inversely related. While both relate to light’s energy, wavelength primarily determines the color we perceive. Amplitude influences brightness; a larger amplitude means brighter light.
Wavelength and Color
Wavelength directly determines light’s color. Our eyes are sensitive to visible light, a specific range of wavelengths within the electromagnetic spectrum, spanning 380 to 750 nanometers (nm). Different wavelengths within this range correspond to different colors.
Red light has the longest wavelengths (620-750 nm), while violet light has the shortest (380-450 nm). The sequence ROYGBIV (Red, Orange, Yellow, Green, Blue, Indigo, Violet) represents this progression. White light, such as sunlight, combines all visible wavelengths. When it passes through a prism or water droplets, it separates into its constituent colors because each wavelength bends at a slightly different angle.
How We See Colors
Specialized photoreceptor cells in the retina detect light and enable color vision. These are rods and cones. Rods are sensitive to low light, allowing vision in dim conditions and shades of gray. Cones require brighter light and enable color perception and fine details.
Humans have three types of cone cells: S, M, and L cones, sensitive to different wavelength ranges. S-cones are most sensitive to short wavelengths (blue light, peaking around 420 nm). M-cones respond best to medium wavelengths (green light, peaking around 530 nm). L-cones are sensitive to longer wavelengths (red light, peaking about 560 nm). The brain interprets the combined signals from these cones to create the colors we perceive.
The Electromagnetic Spectrum
Visible light represents only a small segment of the larger electromagnetic spectrum. This spectrum is a continuous range of electromagnetic radiation, organized by wavelength and frequency. Beyond visible light, it includes radio waves, microwaves, infrared radiation, ultraviolet light, X-rays, and gamma rays.
Each type of radiation has its own range of wavelengths and frequencies. For instance, radio waves have the longest wavelengths and lowest frequencies, while gamma rays have the shortest and highest. Although not perceived as colors by the human eye, wavelength defines and differentiates these forms of radiation across the entire spectrum.