The Nature of Light
Page 5: More Phenomena
Different wavelengths (colors) of light have different refraction angles. For white light, which is a combination of colors, each of the component colors of the white light will have a different refractive index (a different speed of light in the dense optical medium) so that the component colors each have a different refraction angle.
That is why raindrops cause rainbows. Sunlight enters and exits each raindrop through interfaces that are not parallel.
In lens design, the dispersal of light directions, resulting from different refraction angles for different colors, is called chromatic aberration. Lens designers try to account for this by using special shapes and materials.
Polarization is a phenomenon of light that is not usually directly observed by humans. Some animals, however, readily observe and use the polarization of light.
Electromagnetic waves, including light, have electric and magnetic waves. Each electromagnetic wave has an electric wave and a magnetic wave.
Figure 5.2: Electric and magnetic wave. [NASA]
The electric wave is perpendicular to the magnetic wave, and both are perpendicular to the direction of travel of the wave.
Polarization refers to the orientation of the electric field, whether it is vertical, horizontal, or any other angle. Sunlight is randomly polarized, with each photon (electromagnetic wave) having a different polarization. Reflection changes light polarizations depending on the approach angle of reflection.
Polarization causes glare, which some insects use to locate water (by detecting high intensity light with horizontal polarization).
Reflection of sunlight in the atmosphere polarizes the sunlight. Sunlight in the atmosphere becomes most polarized 90 degrees away from the sun. Some insects are able to detect that polarization in the sky, and use that for navigation.
Satellite remote sensing can emit radar signals of known polarizations to see what polarizations are reflected back, to help determine what type of objects are reflecting.