• Visible light consists of electromagnetic radiation of wavelengths about 400 to about 700 nm.
• We perceive different wavelengths of light as different colors.
• Light, like all waves, has a finite speed which depends on the medium it is traveling in.
• B/c the speed of light is very large its measurement is difficult.
• Visible objects are either luminous (emitting light) or illuminated (reflecting light).
• As we move away from a source of light, the intensity of the light decreases by the inverse square law. This occurs because the area the source illuminates increases in the same way the surface area of a sphere increases.
• White light is composed of all wavelengths of visible light.
• Black objects absorb (nearly) all wavelengths of light.
• Objects usually have color b/c they absorb some wavelengths and reflect others.  The reflected wavelengths are perceived as the colors of the object.
• The additive primary colors of light are red, blue, and green.  They produce white light when combined.
• The complementary colors of light are formed from a combination of two of the primaries.  The addition of the third primary produces white light.  The complementaries are yellow, cyan, and magenta.
• A color composed of one or a few wavelengths is said to be spectrally "pure."  Such a color is saturated. If it were mixed with other wavelengths, we would say it is desaturated.
• The brightness of a color is related to the total intensity of the light wave.
• The hue of a color is the name we would give it.
• Pigments and dyes are chemical compounds that absorb some wavelengths and transmits or absorbs others.
• Diffraction of light occurs when it bends around an object in its path.  Diffraction also occurs as light "forces" its way through a thin slit.
• Diffraction produces regular patterns of alternating light and dark areas.  The dark areas are the result of destructive interference (waves lambda/2 out of phase).  The light areas are the result of constructive interference (waves in phase).
• If the light source producing a diffraction pattern contains many wavelengths, many colors will be visible in the pattern.
• Thin-film interference occurs when light reflects off the front and back surface of a material.  Constructive interference produces bands of color in thin films.
• Polarizing materials have an orientation of their make-up that produces an effect analogous to "slots" for light waves. The polarizing material blocks light whose waves are oriented 90° to the slots.

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