The types of artificial lighting you use in photography give you complete control over the direction, quality, and strength of the light. You can move these light sources around, diffuse them, or reflect them. You can alter their intensity to suit the situation.

There are two types of artificial light sources: spotlights and floodlights. Spotlights provide a concentrated beam of light. Floodlights give diffused, softer, more even, spread out light. You can add to these two basic types of artificial light sources. By using lighting accessories, such as reflectors, barn doors, diffusers, and snoots, you can control the light to provide a variety of lighting effects.

Unless special effects are wanted, artificial light sources that are different in color temperature or quality should not be mixed (used together). When you are viewing a scene, your eyes adapt so color differences between two or several light sources are minimized. Color film, however, cannot adapt and shows the color difference in parts of the scene illuminated by different light sources.

Tungsten-Filament Lamps

Tungsten light color films are made to be used with tungsten-filament light sources and are color balanced for 3200 K or 3400 K. Tungsten lamps, operated at their rated voltage, produce light of 3200 K and 3400 K. The color temperature of tungsten lamps changes with voltage fluctuations, decreasing with lower voltage and increasing with higher voltage. For example, the color temperature of a tungsten lamp rated for operation at 115 volts increases about 10 K for each 1 volt increase. Usually, a variation of less than 100 K has no adverse effect on the rendering of scene colors. However, a shift as low as 50 K can be noticeable on subjects with important neutral areas, such as white and light shades.

When you are using tungsten lamps, the color temperature can shift, depending on the amount of power being drawn on the same circuit. When possible, you should avoid having other equipment on the same circuit. For these lamps to produce light of the correct color, they must be operated at exactly their rated voltage. When it is not possible to operate the lamps at their proper voltage appropriate filters can be used to correct the color of the light reaching the film.

Tungsten-Halogen Lamps

Tungsten-halogen lamps have a tungsten filament inside a quartz envelope. This type of lamp does not blacken the inside of the envelope and operates at an almost constant brightness and color temperature throughout its life. Tungsten-halogen lamps for photography operate at color temperatures of 3200 K and 3400 K. Filters can be used to convert them to daylight. For its size, a tungsten-halogen lamp generally delivers more light than a conventional 3200 K lamp. Tungsten-halogen lights are becoming more popular and are rapidly replacing regular tungsten lights for general photographic use.

Fluorescent Lamps

Pictures made on daylight type of color films under fluorescent lights without a filter may be acceptable; however, they usually have a greenish cast. When a tungsten type of color film is used with a fluorescent lamp without a filter, the pictures usually are too blue.

Fluorescent light is not generated by heat, as are other types of light. It has special characteristics different from either daylight or tungsten light. Fluorescent lights have no true color temperature, but a value of approximate color temperature has been worked out.

Daylight fluorescent lamps: 6500 K

Cool, white fluorescent lamps: 4500 K

Warm, white fluorescent lamps: 3500 K

Electronic Flash Lamps

Electronic flash is an excellent light source for both outdoor and indoor photography, especially when the predominant lights are fluorescent. Electronic flash uses a discharge tube filled with xenon gas and is supplied with a powerful charge of electricity from a capacitor. The flash is triggered by means of an electrical current that ionizes the gas. The output, or intensity of the flash, is usually given in effective candlepower-seconds and depends on the voltage and size of the capacitor. The design of the reflector on an electronic flash has a direct relationship on the efficiency of the unit.

Electronic flash resembles daylight in color quality and is excellent for exposing daylight type of color films. The duration of the flash is short, usually 1/500 second or less. With a computerized (automatic) unit used close to the subject, the flash duration can be as

Figure 1-13. A lamp reflector can increase the intensity of light reaching the subject.

short as 1/50,000 second. Computerized electronic flash units have a sensor that switches off the flash when the subject (depending on its distance and tone) has received enough light for proper exposure.