Light is a fundamental part of our daily lives. Understanding why we see different colors involves exploring the basic scientific principles governing light itself.
The Wave Nature of Light
Light behaves as a wave, similar to ripples on water or sound traveling through air. This wave-like behavior means light possesses characteristics such as frequency and wavelength. Frequency is the number of wave cycles passing a point per second, measured in Hertz (Hz). Wavelength is the physical distance between two consecutive peaks or troughs of a wave. For light, these properties are inversely linked: a higher frequency corresponds to a shorter wavelength, and a lower frequency means a longer wavelength. This relationship is consistent because light travels at a constant speed in a vacuum.
Decoding the Visible Light Spectrum
The light our eyes can detect is a small segment of the electromagnetic spectrum, known as the visible light spectrum. Our perception of different colors arises from varying frequencies and wavelengths within this range. When white light, such as sunlight, passes through a prism or water droplets, it separates into its constituent colors, much like a rainbow. This phenomenon, called dispersion, reveals a natural progression of colors: red, orange, yellow, green, blue, indigo, and violet, often remembered by ROYGBIV. The human eye typically perceives wavelengths ranging from approximately 380 nanometers (nm) to 750 nm.
Pinpointing the Lowest Frequency Color
Within the visible light spectrum, red light possesses the lowest frequency and, consequently, the longest wavelength. Its wavelengths generally fall within 620 to 750 nm, corresponding to frequencies around 400 to 484 terahertz (THz). Conversely, violet light sits at the opposite end, characterized by the highest frequencies and shortest wavelengths, typically ranging from 380 to 450 nm with frequencies between 688 and 789 THz. The lower frequency of red light gives it unique properties, particularly regarding its interaction with atmospheric particles. Red light is scattered less by small particles in the air compared to higher-frequency colors like blue and violet. This reduced scattering explains why sunsets often appear reddish; as sunlight travels through more atmosphere, blue light is scattered away, allowing red and orange light to reach our eyes more directly. This characteristic also makes red light useful in applications where light needs to travel further or be more easily seen through scattering mediums, such as traffic signals.