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# Visible Light

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 Sub Topics Light has intrigued humans throughout history. Prehistoric humans were undoubtedly aware that the Sun and heavenly bodies provided light and that could ward off nightly dangers. While we all have a familiar understanding of light, it can best be understood scientifically as a type of electromagnetic wave. An electromagnetic wave consists of two parts: an electrical part and a magnetic part. Electromagnetic waves with wavelengths ranging from 400 nm (violet) to 700 nm (red) comprise visible light. The frequency of visible light ranges from 4$\times10^{14}$ Hz (red) to 8$\times10^{14}$ Hz (violet).

## Definition

The visible light region occupies only a very small portion of the total electromagnetic spectrum. The visible spectrum covers a range of less than 4% of the width of the electromagnetic spectrum. It runs from a frequency range of 4$\times10^{14}$ Hz to about 8$\times10^{14}$ Hz or a wavelength range of 700-400nm respectively. Visible light emitted or reflected from the objects around us provides visual information about our world.

## Sources

• Visible light can be emitted by many sources, such as an incandescent bulb or a hot metal filament.
• The resulting board emission spectrum is referred to as thermal radiation and it is one of the major sources of light.
• Light is also generated by passing an electric discharge through a gas filled tube. The atoms of the gas will become excited and emit a stream of photons as visible light.

## Wavelength

The average wavelength of visible light is about 0.0005 mm. This means that roughly 50 light waves would fit end to end across the thickness of a sheet of household plastic wrap. The wavelength of visible light ranges from about 400 nm to 700 nm (4000 to 7000 A°). Just as you sense the wavelength of sound as pitch, you sense the wavelength of light as color. Light with wavelengths at the short-wavelength end of the visible spectrum looks violet to your eyes and light with wavelengths at the long wavelength end looks red.

## Visible Spectrum of Light

Energy from light is radiant energy, energy transmitted by electromagnetic waves. Types of radiant energy include infrared rays, radio waves, ultraviolet and X-rays. We only see a tiny part of all the different kinds of radiant energy; the part we see is called the visible spectrum. Light is visible only when it is the source of light itself or when it is reflected off something else. Visible spectrum includes the colors from violet to red according to the order or wavelength or frequency. Given figure shows the visible spectrum of light.

## Energy

Absorption of a photon of visible light by a compound results in the excitation of an electron from a low energy orbital to a higher energy orbital within the substance. In order for the photon to be absorbed, the difference in orbital energy levels must match the energy of the photon absorbed. Finally, the excited electron must be able to be excited to the higher energy orbital-that is, the higher energy orbital must not be full. For example, when visible light strikes rust, an electron in a lower energy orbital absorbs a photon of blue light. The electron is excited to a higher energy orbital. Orange light is reflected and that is what our eyes detect. Rust is orange colored. The equation for energy of visible light is,
E = h$\nu$
where E is the light energy
h is the Planck's constant
$\nu$ is the frequency

## Uses

Some of the uses of visible lights are:

• Indispensable for writing, reading etc.
• Helps to avoid stepping in stuff
• Photography
• Medical uses
• Helps to observe things

The examples of visible lights are: violet light, red light, green light etc

The radiation we are able to detect with our eyes falls into the rather narrow frequency range from 4$\times10^{14}$ Hz to 8$\times10^{14}$ Hz, corresponding to wavelengths from about 700 nm to 400 nm. This radiation is called visible light. The color of visible light varies systematically with its frequency. Visible light radiation is comes under nonionizing radiation. Nonionizing radiation is associated with radiation that does not have enough energy to cause ionization. It also be referred as optical radiation; the wavelengths are generally expressed in nanometers.