Light
Light is a fundamental part of our world. The uses of light are endless, it can be used to transmit data, change the mood of a space, perform surgery, and cook food. Light is the reason we see the world the way we do, but what is light?
History
People have attempted to explain light in many different ways. The earliest idea, held by Ptolemy, Euclid, and Hero, was that, “the rays [of light] originate in the eyes and travel to the object that is seen” (Physics). This was the accepted idea, until the 10th century when Alhazen discovered that, “light rays are emitted by a luminous source and are then reflected by objects into the eyes” (Physics). Seven hundred years after Alhazen, Newton discovered that white light was made of a combination of all the colors. Newton also claimed that light was made up of a “stream of particles” (Physics). This was challenged by Huygens, who said that light was made of waves. Huygens was later proven to be correct by Fresnel.
Radio waves, gamma rays, x-rays, and light are waves that make up the electromagnetic spectrum. Waves are forms of vibrations and are not made of matter. The difference between them is wavelength and frequency. Wavelength is the distance between two crests of the wave, and frequency, measured in hertz, is the number of times the wave oscillates between crests per second. These can be expressed in relation of one another as 
Color
Light is the visible portion of this spectrum and it ranges from a frequency of 350nm to 800nm. These frequencies correspond to different colors of light ( Figure 1). The bottom end of the visible spectrum starts at violet, which changes to blue, to green, to yellow, to orange, and lastly to red at the upper end.
Figure 1
The visible spectrum
Source: Apollo Design Technology
White light is light made up of every color of light. Colored light is white light that has had certain wave lengths of light removed while leaving only others. This process is called subtractive color mixing and is usually accomplished with a color filter called a gel. In subtractive mixing, the colors cyan, magenta, and yellow are used to form all other colors. Additive color mixing is the opposite of subtractive. Instead of starting with white light and then removing light, it begins at black and different colors of light are added. In additive color mixing with light, the colors red, green, and blue are used to create all other colors. An example of additive color mixing would be mixing two different colored beams of light one green and one red to produce yellow.
Reflection and Refraction
Besides color, another aspect of light is its interaction with other objects. These interactions are called reflection and refraction. Reflection is when “a wave hits the boundary and returns immediately to its original medium” (“Refraction”). Light strikes a material at an angle called the angle of incident. It then bounces off at an angle called the angle of reflection. The angle of reflection and the angle of incident are equal to one another and share a ray perpendicular to the surface of the material (Figure 2).
Figure 2
Snell’s Law
Refraction is the bending of light; this is often achieved with lenses. Refraction is caused by a ray of light going from one material to another. The angle of refraction is explained in Snell’s law, 
Light comes in all sorts of forms for all kinds of functions from data transmission to theatrical lighting. It comes in so many forms because of color, intensity, and focus. Light has uses everywhere from lasers to food preparation, to fiber optics. Light is an integral part of the world today.
Sources
Dijksterhuis, Fokko J. “Light Transmission.” EBSCO. N.p., 2000. Web. 15 Apr. 2010.
“Light.” EBSCO. 6th ed. N.p., 1 Oct. 2009. Web. 22 Apr. 2010.
“Light; Colors of the Spectrum.” World Almanac. World Almanac Education Group, 2009. 1152. EBSCO. Web. 27 Apr. 2010.
Physics. Spec. issue of Physics (2006): n. pag. EBSCO. Web. 10 May 2010.
“Reflection.” American Heritage Student Science Dictionary. Boston: Houghton Mifflin Harcourt Publishing Company, 2009. EBSCO. Web. 10 May 2010.
“Refraction.” American Heritage Student Science Dictionary. Boston: Houghton Mifflin Harcourt Publishing Company, 2009. EBSCO. Web. 10 May 2010.
“Refraction.” EBSCO. 6th ed. N.p., 1 Oct. 2009. Web. 8 May 2010.
