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# Visible light

Visible light is the form of light that we see with our eyes. They are electromagnetic waves that are seen as a rainbow. Light is broken up when going through a prism, then each color goes in a different direction depending on the wavelength. Red has the longest wavelength and violet has the shortest. [1] The frequencies of visible light range from 4-7.5 X 1014Hz. Although there are several different colors of visible light, there are many kinds of light that cannot be seen. The best examples of these would be infrared, ultraviolet, X-rays, and gamma rays.[2]

There are many ways that light can be used for us. An example is a lasers. Lasers can be used in printers, CD's, DVD's, and satellites. In satellites they can be used to gather data to calculate the elevation of Earth's polar ice sheets, and determine how much water is in them. They can also be used to find information about clouds. [1] Using visible light we can see reflection and refraction along with interference and diffraction. Various objects have been made to help use and understand light better. Some tools are mirrors, prisms, lenses, diffraction gratings, and spectrometers all help understand the light that we see with our eyes. [3] There are more then just real colors in satellite images, there can also be false colors. False colors are recorded by the brightness of an image. The brightness is recorded in a numerical value, then color coded. [4]

## Properties

A prism which causes light to split into the light spectrum

Visible lights are the only electromagnetic waves that can be seen with the human eye. The visible light is seen as a rainbow. When light shines through a prism the light is broken up by wavelength and is seen as the colors of a rainbow. This is because the prism separates the wavelengths and sends them out at different angles resulting in the different colors. Each color of the rainbow is a different wavelength of the electromagnetic spectrum. Red has the longest wavelength, and violet has the shortest. [1] The frequencies of visible light range from 4-7.5 X 1014Hz. Wavelengths of visible light are from about 750-400 nm. Its quantum energies are 1.65-3.1 eV.[2]

The main source of light is from the sun. This is the most common light that we see with our eyes. The sun's corona, which is the outer layer of the sun, can be seen in visible light. However it is very faint and usually can only be seen during a solar eclipse. The hotter an object is, the shorter the wavelength it produces. An example is a blowtorch of which the flame can change from red to blue as it grows hotter. The sun appears yellow because it is about 5,600 degrees. If the sun were hotter, for example 12,000 degrees C, it would be blue like the star Rigel. On the other hand if the sun were not as hot, say 3000 degrees C, it would be red like the star Betelgeuse.[1] Light waves are emitted by anything that is hot enough to glow. Light bulbs work when an electric current heats the substance inside the lamp to about 3000 degrees C. The result causes the light bulb to glow a bright white. Another example includes cinema projectors which use a powerful filming lamp that has a "color temperature" of 3000K. [5]

## Non-visible light

Gamma Ray Burst

Although we see only visible light, there are light waves that can't be seen by the human eye. Some of these include infrared, ultraviolet, X-rays, and gamma rays. Infrared is a broad range of frequencies used for communication. Infrared wavelength is from 1mm-750nm. The section of infrared close to the visible spectrum is called the near infrared, and the section farther is called the far infrared. Infrared sets molecules into motion. Infrared spectrometers are used to study these vibrations caused by infrared. Infrared does not travel through the atmosphere well. Ultraviolet is below the visible spectrum. Ultraviolet wavelength are from 400nm-10nm. Most solid objects absorb ultraviolet light strongly. It is even absorbed by air. Short wavelengths of ultraviolet light reach the ionization energy for lots of molecules. The far ultraviolet can cause ionization radiations. Some effects on the human tissue include sunburns, and some therapeutic effects. Ultraviolet radiation is mostly dispensed from the sun but luckily most of the shorter ultraviolet wavelengths are eliminated by atmospheric absorption. Ultraviolet rays also can damage our eyes. Because of this welders wear protective masks because the UV in welding arcs can cause severe damage to the eyes. Also when it is really sunny and the ground is covered in snow, it can be dangerous because the snow reflects UV rays.[2]

X-rays are very strong rays that are formed when high energy electrons hit a metal target. They are commonly used to treat broken bones. We know that they are high frequency electromagnetic rays produced when electrons are decelerated. They can also be made when electrons transition between lower atomic energy levels in heavy elements. Characteristic X rays have energies determined by atomic energy levels. X-rays wavelengths are 10nm or lower. Gamma Rays denote electromagnetic radiation from a nucleus as part of the radioactive process. Gamma rays wavelengths are less than 10-12m. Nuclear radiation energy is very high because the radiation between electromagnetic force and the nuclear strong force causes an intense conflict. A gamma ray photon is similar to an X-ray. Gamma rays are ionizing radiation that can produce physiological effects which aren't seen with non-ionizing radiations, like cancer in tissue, or mutations.[2]

## Uses

A laser printer

As light waves are sent from the sun, we have changed and can use these for our own purposes. An example of using visible light is laser altimetry of active remote sensing. NASA has a satellite called the Ice, Cloud, and land Evaluation Satellite (ICESat), which contains a Geoscience Laser Altimeter System. It uses lasers and ancillary data to calculate the elevation of Earths polar ice sheets. These changes in elevation can be used to determine the amounts of water stored in ice. Laser altimeters can also be used to measure the height and characteristics of clouds. They are also used to study the canopy of forests, and dispersion of substances from things like forest fires and dust storms. [1]

Using visible light we can see reflection and refraction along with interference and diffraction. Various objects have been made to help use and understand light better. Some tools are mirrors, prisms, lenses, diffraction gratings, and spectrometers all help understand the light that we see in our eyes. Galileo's telescope uses refractive properties to magnify light and make it easier to see distant objects. Today basic telescopes and binoculars use the same method of total internal reflection. [3] Light waves can be made using a laser. Lasers produce coherent light, instead of a light bulbs light. Lasers are used in printers, CD's, or DVD's. Light is reflected from the tiny pits in the disc. The pattern is detected and translated into either sound or data. [5]

## False colors

Double slit x-ray simulation polychromatic false-color

Although satellite data can show true colors, it can also show another kind. These are called false colors. True colors are seen when a satellite scans the red, blue, and green visible light waves that bounce off earths surface. But false colors are when the satellite records data about the brightness of the light. Different brightness is recorded on a numerical value, which then is color coded. The colors could make it look realistic, or display a certain feature in the image.[1]

Here is a description of what false colors do to show an image. The way human eyes see a planet, it appears as only one color. True color can be processed through filters to record data about the planet. False color and extreme contrast can be used to bring out the polar regions in an image. The greatly exaggerated colors can also be used to study the clouds on a planet. [1] by Josephus

## References

1. Netting, Ruth. visible light waves Visible light waves. Web. Date of access March 31, 2014.
2. Nave, R. Infrared Electromagnetic spectrum. Web. Date of access March 31, 2014.
3. Villanueva, John Carl. university visible light. Web. Date of access April 3, 2014.
4. Visible light NASA. Web. Date of access April 3, 2014.
5. Browser, Safeguard. spectrum The electromagnetic spectrum. Web. Date of access March 31, 2014.