# Wavelength of Light

## Light

Commonly referred to as visible light for less ambiguity, light is the electromagnetic radiation that is part of the electromagnetic spectrum, which can be perceived by the human eye. Visible light has wavelengths in the range of 400 - 700 nanometers (nm) and frequency values between 430 and 750 terahertz (THz). Visible light is characterized by properties like intensity, propagation direction, frequency or wavelength spectrum and polarization. All types of electromagnetic radiation, including light, has a speed of 299,792,458 meters per second (m/s) in the vacuum. This value of light, often denoted by the letter ‘c’, is a fundamental constant in physics and related fields. It is extremely important to mention ‘visible’ when addressing light waves that are perceivable by the human eye because, in physics, the term light refers to any electromagnetic radiation of any wavelength like for example, gamma rays, X-rays, microwaves and radio waves are also light, even if the light waves are visible or not. Light demonstrates both particle and wave characteristics, and this is referred to as the dual nature of light or also called the wave-particle duality. As is the case with any electromagnetic radiation, light propagates through free space in the form of waves, but on impact with the target or any obstacle, it imparts energy as particles do; the energy is absorbed in single locations. This energy imparted is in the form of photons, and this represents the quanta of light. The study of light is known as optics.

## Wavelength of Light

Wavelength is defined as the measured distance between two identical points on two successive waves. Wavelength can be measured either between two successive crests or two successive troughs. Light propagates through free space in the form of transverse waves; the direction of motion of the wave is perpendicular to the direction of oscillation of the photons. Wavelength is represented by the symbol λ (lambda), and the units are nanometers (nm) or micrometers (µm). The wavelength, in the case of waves, can be expressed as follows.

### λ = c/f

Or in the case of particles as

### E = hf

where

• λ = the wavelength of light
• c = the speed of light in free space/ vacuum
• f = the frequency with which the photons in the light wave oscillate
• E = the energy of the light wave
• h = the Planck’s constant (6.64 x 10-34 joule/ second)

Visible light comprises multiple different wavelengths, and each wavelength corresponds to a different color. The color of objects humans perceive is a result of the reflection of light waves by that object. The molecules of an object absorb all other wavelengths of light except one, which is then reflected by it and perceived by the human eye in color specific to that wavelength. The sun, which is the primary source of light for our planet, produces polychromatic light. That is, the light waves from the sun are considered to be white, which is the combination of all the seven visible light spectrum colors. However, in the case of lasers, the light produced will be one specific color, and is called monochromatic because the color of the light depends on the wavelength. The seven colors of the visible spectrum are violet, indigo, blue, green, yellow, orange and red.

## Visible Spectrum of Light

 Color Wavelength (in nm) Frequency (in THz) White 750 - 400 790 - 400 Red 750 - 610 480 - 405 Orange 610 - 590 510 - 480 Yellow 590 - 570 530 - 510 Green 570 - 500 580 - 530 Blue 500 - 450 670 - 580 Indigo 450 - 425 600 - 670 Violet 425 - 400 700 - 790
• White light: White light's wavelength ranges from 400 to 750 nm. When the white color is passed through a crystal structure like the prism, the light spectrum is formed by refraction of different wavelengths through different angles.
• Red Light: The wavelength of red light is in the range of 750 - 610 nm. The sky can appear to be red during sunsets and sunrises when the Earth’s atmosphere improperly scatters the incoming sunlight.
• Orange Light: Orange lights have wavelength values that can vary anywhere between 610 to 590 nm. Much like red, the color of orange can also be observed during sunsets and sunrises.
• Yellow light: Yellow light can be seen emitted by zero-watts bulbs that have a tungsten filament in them, and sometimes also during sunsets and sunrises because they are close in value to red and orange lights.
• Green light: The wavelength of green light lies between 570 – 500 nm. Green color can be seen in trees and other vegetation.
• Blue light: Blue light has the appropriate wavelength values that help them to be scattered by the atmosphere much more easily. Hence, the sky is blue.
• Indigo light and Violet light: Since the wavelengths of both colors are almost identical in value; they appear to be slightly similar.
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