Most lighting require a key light and a fill light. The key light is the main light source and is generally set at about a 45 degree angle from the camera. The fill light is about 2/3 the intensity of the key and is set about 45 degree on the opposite side of the camera. The fill does not need to be an actual lamp. A reflector works just as well. For example, if a photographer is using sunlight as the key then a reflector would be more than adequate for the fill.

The key light sets the tone of the shot. It is the brightest light of the set. All shadows and other indicators of depth and distance will be based on the position of this one lamp. Every other lamp on the set complements the key so placement is of absolute importance.

But where does one place the key? Generally the key is placed about 45 degrees to the side of a line between the camera and the subject and a little above the subject. The stand should be just even or forward of the camera to avoid errant shadows from the photographer.

The colour can be any colour the photographer chooses but should complement the subject (i.e. using a bluish color for blue or black inanimate objects, using white for people, etc.). The colour can also simulate other environmental conditions such as using an orangeish yellow to simulate sunrise/sunset. However, one is most safe by sticking with the standard 1500 degree Kelvin white and letting the fill lights use colour to set the tone. There may be circumstances where using white is inadequate for the key.

The fill light has two roles. First, it fills in the deep shadow areas where the key light does not reach to reduce contrast. Second, it helps set the mood of the shot.

The fill light is set at the same heighth as, and about 45 degrees on the opposite side of the camera from the key. It is about 1/2 to 1 f-stop dimmer than the key. If the meter indicates f-11 with just the key then the fill will indicate f-8 or smaller by itself.

To compare intensity the fill will be as intense to the key as the moon is to the sun. Since the moon is merely a reflector of the sun’s light then it follows that a reflector may be used as the fill light. The fill or reflector can be white, aluminum, gold, copper, or any color that the photographer wishes as long as it supplies sufficient light in the shadow areas. Any shadows cast by the fill light must remain out of the frame.

In portraiture the high light, also called the “hair light” is placed directly above the subject pointing straight down to reflect off the subject’s hair (if any) which gives depth to the photo. It helps to “separate” the subject from the background. The intensity is about the same as the fill light but, since it is so much closer to the subject, appears nearly as bright as the key. Therefore, it’s relative position to the subject resemble the key’s.

Background lights help to separate the subject from the background. The also help in perspectives. For example, a background may indicate the subject is in a long hallway but it is just a painting. Perspective is ruined if the subject’s shadow is cast on the far wall. Background lights are also useful to prevent the photographer’s reflection in a highly reflective background.

Background lamps are usually placed on the floor or above the background at very steep angles to the background to eliminate reflections from the lights. Background lamps can also be placed behind a transluscent background to brighten it up, such as a simulated computer or television screen.

A black reflector is used when one is photographing very reflective or clear items. Glassware, coins, fine china, jewelry, and silverware benefit when being photographed using a black reflector. The reflector is placed near the fill light but it does not supplant the fill. The black reflector provides an edge contrast to provide separation from backgrounds. The black reflector also lets the viewer see details in engraved or embossed pieces. A black matte such as felt works best since the objective is to remove illumination from the edges.

I recommend The Lighting Cookbook that can be purchased at most bookstores or Adorama http://www.adorama.com/BKTLCB.html for graphical depictions of typical lighting requirements.