How many colours does white light consist of and what are they?

White light, often associated with purity and simplicity, is far from being simple when dissected through the lens of physics. In essence, white light is a mixture of all the colors that the human eye can perceive. When rays of white light hit an object like a prism, they undergo a process called dispersion. This process separates the light into a spectrum of colors, revealing the hidden complexity of white light. Each color that emerges has a particular wavelength, and when these wavelengths are combined, they give us the white light we are familiar with.

Experiencing White Light in Nature

A common natural phenomenon that showcases the composition of white light is a rainbow. After a rainstorm, droplets of water in the air act as tiny prisms that break the sunlight into its constituent colors, offering a splendid display of the light's true diverse nature. Understanding the makeup of white light is not only essential for comprehending various optical phenomena but also serves as a foundational concept in the study of light and color in physics.

The electromagnetic spectrum comprises a range of different kinds of energy waves characterized by their wavelengths and frequencies. Visible light is just a small portion of this extensive range, which includes other types of waves like radio waves, microwaves, infrared radiation, ultraviolet light, X-rays, and gamma rays.

Visible light sits between infrared and ultraviolet light on the spectrum. The human eye has evolved to detect this particular range of wavelengths, approximately from 380 nanometers (nm) for violet light to 750 nm for red light. Beyond the visible spectrum, other waves are not perceptible to the naked eye but play critical roles in technology and the natural world. For example, radio waves are crucial for communication, while X-rays are used in medical imaging. Understanding the electromagnetic spectrum helps us to comprehend the full range of electromagnetic radiation that surrounds us, only a fraction of which we can visually experience.

The colorful acronym 'ROYGBIV' encapsulates the continuously varying hues that constitute the visible spectrum of light. The sequence starts with Red, boasting the longest wavelength, and ends with Violet, which has the shortest wavelength. The colors follow the order of Red, Orange, Yellow, Green, Blue, Indigo, and Violet–a range that mirrors the decreasing order of wavelengths and energies.

Why Red Signals Caution

One may wonder why red light, with its longer wavelength, is used in stop signs and traffic lights to signal caution. It is because red light waves disperse less in the atmosphere compared to shorter wavelengths, making red signals visible from a distance. This property of red light gives it priority in safety signaling. The ROYGBIV colors are not just a mnemonic for remembering the colors of the rainbow but also represent the varying energy levels across the visible spectrum. Each color has its own unique wavelength and related energy, and together, they weave the tapestry of color that the human eye can detect.