Light is a form of energy that travels through space in waves. The specific color we perceive is linked to the physical characteristics of these waves. Every distinct color represents a different energy level, determined by how frequently its wave oscillates. Understanding this relationship is key to identifying the color at the lowest end of the light spectrum.
Defining Light and Color Frequency
The primary physical properties used to describe a light wave are its frequency and its wavelength. Frequency refers to the number of wave cycles that pass a fixed point in one second, and it is measured in units called Hertz (Hz). Wavelength is the physical distance between two consecutive peaks of the wave, commonly measured in nanometers (nm).
These two properties share an inverse relationship: as one increases, the other must decrease. High frequency results in a short wavelength, while low frequency results in a longer wavelength. Furthermore, frequency is directly proportional to energy; a high-frequency wave carries more energy than a low-frequency wave.
The Lowest Frequency Color Red
Red light is the color with the lowest frequency within the spectrum visible to the human eye. This means red light waves possess the longest wavelengths of all visible colors, typically ranging from 620 to 750 nanometers. Red light sits at the boundary of what humans can detect.
These long wavelengths correspond to the lowest visible frequencies, spanning approximately 400 to 484 Terahertz (THz). Since frequency and energy are linked, red light carries the least amount of energy compared to other visible colors. When ordered by increasing frequency, the visible colors start with Red, followed by Orange, Yellow, Green, Blue, and Violet (ROYGBIV).
The visible spectrum places red at the end where waves are longest. The transition from red to violet marks a continuous increase in frequency and a corresponding decrease in wavelength. Red is the terminus before light waves transition to a frequency too low for the human eye to register.
Context on the Electromagnetic Spectrum
The visible spectrum is a very narrow band within the much larger Electromagnetic (EM) spectrum. The EM spectrum includes all types of light waves, organized by their frequency and wavelength. While red light has the lowest frequency of all visible colors, it is not the lowest frequency of light waves overall.
Immediately adjacent to the red end are light waves with even lower frequencies called Infrared (IR) light. Infrared waves have frequencies lower than 400 THz and wavelengths longer than 750 nm, often perceived as heat. Beyond infrared, the EM spectrum continues to drop in frequency through microwaves and then to radio waves, which have the lowest frequency and longest wavelengths.