PROPERTIES OF ARTIFICIAL LIGHT
by William Lulow
Artificial light is normally produced by light bulbs of one variety or another. The most common are household utility light bulbs which range in intensity based on how many watts they supply. Artificial lights for photography work the same way with the exception of non-continuous light sources such as electronic flash or strobes. Light from a continuous light source, such as an ordinary light bulb by itself would scatter light rays all about the room in a generally haphazard way with approximately a 360-degree field. When we are considering lighting a subject for a portrait, this type of light would yield a flat, low contrast looking picture with little definition and no directional shadows. The purpose therefore, of using certain reflectors with these light sources is to aim the light in whatever direction we want in order to create definition and detail and focus the light to hit certain parts of our subjects. Also, by using these reflectors, we create shadows on our subjects which can be used for various purposes.
So, the first important property of artificial light for portraits is that whenever a reflector of some type is added to a bulb, the light is given some direction. The tools available to us for directing light in various ways are the following:
(2) Spotlights with lenses,
(4) Light diffusers (spunglass, frosted acetate, plastic),
(5) Light Banks,
(6) Light projectors,
(7) Snoots and cones,
(9) Reflector Cards,
(10) Barn doors and Gobos,
(11) Strobes (Electronic Flash).
Each of these items produces light of different types and qualities. For instance, one 500 watt floodlight mounted in a socket with a metal reflector of 12″ or so in diameter, produces a very bright, harsh light. The reflector acts to direct the light in a fairly broad pattern (somewhere in the vicinity of 100 degrees) .
This would be a broad enough pattern to light a person’s face fairly well. If we wanted to light just the person’s eyes say, we would obviously need a somewhat narrower reflector to keep some of the light off the other facial features. This would call for a smaller, narrower reflector. Probably something like 4″ or 5″ would do the job. Another way to control the light from a large reflector is to set up barn doors or “gobos.” A barn door is simply a dark card which is placed over part of the light to cast a selective shadow on the subject. It can be moved back and forth or in and out so the effect is just right. Similarly, a “Gobo” is a black card which “goes between” the light and the subject in much the same way as a barn door. Obviously, the spread of the light from the two different reflectors or the “gobo-ed” light would be very different. In the same way, light from the same reflector can be different in quality as well as direction and intensity. For example, if I took that same 500 watt floodlight and put a piece of spunglass over it, the resulting light would be softer, less harsh and more diffuse. The spunglass would act as a diffusion material, scattering the light rays even further and producing that softened effect. This can be very useful to the portrait photographer who is trying to flatter the subject with very soft light. (More about flattery later). Light can also be altered by each of the other tools mentioned above. There is a great difference however, in the quality of light given off by strobe light (Electronic Flash) and continuous light (Hot Light). Strobe light is non-continuous light created when a generator, consisting of several large capacitors, resistors and electronic relays, stores electricity until it is needed. When the photographer snaps the shutter, all the stored electricity is routed through the flash tube in the flash “head.” Gases in the tube glow very brightly but very briefly when the electricity hits it. This all produces a very short but intense “flash” of light. This single flash is many times brighter than our 500 watt flood light. Also, due to the short duration of the flash, (usually 1/400th of a second or shorter) it is able to “freeze” most action in the photograph. However, the effects of the light are exceptionally hard to distinguish for the naked eye. Another difference between hot light and flash is that the former is on all the time and the latter is on only when the picture is taken. If you have ever sat under a 500 watt floodlight you can imagine how uncomfortable it could get for a subject sitting for a whole portrait session with it on. Electronic flash therefore, is usually much more comfortable for the subject. Even though this is a distinct advantage, the disadvantage is that electronic flash units are much more expensive than hot lights and it takes a lot of power to run them. It is also more difficult for the photographer to preview the lighting without actually taking a picture.
So, the best way to learn the effects of lighting is by using hotlights. You can then transfer the knowledge to strobes.