Daylight

Figure 1-10.–Controlling polarized light. when a section of line is secured at one end and the free end is held in your hand and given a shake, a wave travels down the length of the line from the end that was shaken to the secured end just like an oscillator. A light source acts as an oscillator. The wave motion in the line, however, does not represent the true wave motion of light because light waves move in all possible directions at right angles to their direction of travel. A much clearer picture of light wave motion can be seen by having a number of parallel lines with each one being shaken in a different direction-one up and down, one sideways, and the others at various angles in between. Ordinarily, light waves vibrate in all directions at right angles to their direction of travel. However, when light waves strike a series of parallel microscopic slots, all the light that passes through vibrates in one direction. This is polarized light. Filters that polarize light, termed polarizing filters, have a practical use in photography (fig. 1-10). Specular reflected light, from a nonmetallic surface at any angle between 32° and 37°, is polarized in such a manner that the light rays vibrate in a direction parallel to the reflecting surface. Light reflected in this manner is said to be plane polarized and is seen as glare (fig. 1-11). There is no polarization whatsoever produced by reflections from metallic surfaces. LIGHT SOURCES In the beginning of photography, daylight, or sunlight, was the only light source suitable for exposing the slow film available at that time. Today, photographic film is not only vastly more sensitive to light, but a wide range of light sources have been developed for the needs of the photographer. These light sources include the following: tungsten lamps, tungsten-halogen lamps, fluorescent lamps, and electronic flash. DAYLIGHT Sunlight, of course, is the light photographers are most familiar with and for good reason. It is the light they use the most. Naturally, sunlight is the only practical light source for general outdoor photography. Artificial light sources, however, can provide useful supplementary lighting to sunlight as fill-in for shadows (to make them lighter) and take the place of sunlight entirely for photography of small areas and close-ups. Sunlight is often referred to as daylight. The term daylight, as used in photography, is meant to include all Figure 1-11.–Light, plane polarized by reflection. 1-7