Basic Optical Principles
Wave Length & Frequency / Refraction of Light

Light travels at the rate of about 186,000 miles per second in air. There are two theories which explain how light is propagated. Both theories are necessary to describe how light behaves under all circumstances.

Wave Theory: Put forth by Christian Huygens in the late 1600�s describes light as moving in waves, very much like the motion of waves in water.
Corpuscular Theory: Described by Isaac Newton also in the late 1600�s describes light as being minute particles which originate from the light�s source. These tiny particles are called photons.

 

Rays of light diverge and radiate outwardly in all directions from their source. Light can be said to travel in waves.

Wavelength: The distance from the crest of one wave to the crest of another.
Frequency: The number of times the crest or trough of a wave passes a point in space in a given unit of time.

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Refraction of Light

When light enters any given transparent material which is denser than air, the velocity of light in that material is reduced. If it enters the new medium at an angle parallel to the normal, as in Figure A above, the light is slowed down while it is in the new material then resumes its original speed after exiting. The direction of the light does not change. If it enters the material at some angle other than parallel, the direction of the light is altered as it exits the denser medium. The denser the material, the more the light is slowed down and the more it is deviated from its original course. The density of any given material can be expressed as index of refraction.