All electromagnetic waves travel through free space at the same speed, c = 3x 10⁸ m/s. The difference between radio waves, light, x-rays etc. is in their wavelengths. Our eyes are sensitive to electromagnetic waves whose wavelength covers the range of approximately 3.8 x 10^-7 m (380 nm) to 7.5 x 10^-7 m (750 nm).

The color of a beam of light is determined by the wavelength of the oscillations that are present. Violet light has shorter wavelengths (380 to 440 nm) than red light (629 to 750 nm). The light-sensitive cells called cones that are located near the center of the retina detect color. White light consists of a mix of various wavelengths, and an appropriate mix of the three primary colors blue, green, and red produces it.

Materials can selectively absorb specific colors whenever white light strikes them, thereby removing that color from your perception of the color of the objective. Different materials absorb different colors. Materials also scatter different wavelengths of light through different angles which results in the object appearing to have a different color.

Whenever two waves occur in the same region they can interfere with each other. The interference may be constructive in which case the effect of each wave is enhanced or destructive in which case the waves tend to cancel each other. Interference patterns of light can be produced by thin films (the films must be thin because the wavelength of light is very short).

The effect of a beam of light can be observed beyond a narrow slit in a why in which it appears that the light was "bending around corners." This phenomenon is called diffraction. The dimensions of the slit must be comparable to the wavelengths of the light involved. Diffraction gratings have many small slits for producing such diffraction patterns.

Polarized light has the electric field vector pointing in particular directions as shown in Figure 16.22 in the text.

For some materials, e.g. calcite crystals, the speed of light in one direction through the crystal is different than the speed in another direction. The result is the production of two images whenever an object is viewed through such a crystal. This phenomenon is called birefringence.