Illuminations: Casting Shadows

Robert G. Nulph, Ph.D.
July 2007

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Did you ever think about where you wanted to place the shadows or how you could add shadows to your images to make them look less flat and more realistic? TV is a two-dimensional medium. In this column, we will focus our attention on the shadow - how you can manipulate its look and density - and we'll look at some ways in which you can cast it to create a more three-dimensional feel to your images.

A shadow is an area of darkness created by an object that passes in front of a light source. The position of the object in relation to the cast shadow, the type of light being blocked and the amount of other light in the area all affect the quality of the shadow.

The first and most important factor you have to remember about a shadow is this: the closer the object casting the shadow, the sharper the shadow's edge. Even with a large soft light source, you can cast shadows if the object you are using is close enough to the surface that you want to shadow. When shooting a scene, the shadow-casting object can be just out of the shot, getting it close enough to the scene that the shadow it is casting is sharp and clear.

The type of light you are using is very important when casting shadows. Small intense lights create a hard-edged light that casts very sharp shadows. Set your lights on spot, and the shadows you are trying to create will have sharper edges. Large soft lights create a very diffused light that does not provide a good shadow.

The density or darkness of your shadow depends entirely on the amount of ambient light falling on the shadowed area. If you are able to control all of the light falling on a surface, the shadows that you cast will be very dark and dense. However, any other light in the area will reduce the density of the shadow and turn it from black to gray.

You can also create colored shadows. Normally, shadows are black or gray. However, you can create green shadows by casting a shadow with a red light and illuminating the shadow with white light. As you add the white light, the shadow will turn green. As you see, light will either color the shadows or brighten them, and the resulting color is the complementary color to the light that is blocked to cast the shadow. The complement of red is green and vice versa. For a blue shadow, use orange light: you can create a yellow shadow by using a purple light.

There are a number of tools you may want in your shadow-casting tool kit. A cookie or gobo (short for go between) is a piece of black foamcore, plywood or other sturdy material, shaped or cut to create a patterned shadow when placed between a light and the background to be shaded. Windowpanes, doorways, leaf patterns and fence-rows are just a few of the many types of gobos you might want to use as background shadows.

Another type of gobo is a small metal slide used in a pattern projector or theatre leko. This metal slide has intricate designs cut into the metal, so that it can project tree leaves, fireworks, company logos or thousands of other designs. The leko, which is an ellipsoidal light fixture, is capable of focusing the design shadow very sharply on any surface.

Another shadow-casting tool is the flag. This is a piece of black foamcore or metal-framed opaque black cloth used to place shadows on the background and control your light sources.

Dots are another useful tool. Like flags, only smaller, dots are small circular pieces of metal or foamcore used to precisely place shadows at particular points in your image.

Now that you know the facts about shadows and the tools used to manipulate and cast them, how do you use that knowledge to make your images look even better? Let's take a look at some simple but standard lighting situations you may encounter.

You are doing an interview, and you want to create an interesting background, but you don't have any nice drops or props to use. How about a nice dappled shadow background to add that three-dimensional look?

Set up your typical three-point lighting with a nice soft light for the key, a back light opposite the key giving your talent's hair and shoulders a nice rim light, and finally a bounce card to provide a little extra fill light to fill in any dark shadows on the face. Set up another light so that it is focused on the blank back wall behind your talent. Cut an irregular branching organic design in a piece of black foamcore and place it between the light and the wall. Adjust the placement, size and sharpness of the shadow by moving it closer and further away from the wall, always making sure it is out of camera shot. Look through the viewfinder to decide on the look you want. Simple as that, you have turned a flat ugly wall into a three-dimensional background. (See Figure 1.)

What if you are shooting a movie and want the shadow of a doorway or windowpane in the background? Set up your shot and place a small, hard light so that it lights up the area on the set where you want the shadow. Place a door-shaped or windowpane-shaped gobo as close to the set as possible, keeping it out of the shot. Adjust its position to achieve the desired effect. Keep in mind that you don't need a real-sized window to create the shadow. The further away the gobo, the bigger the shadow. Use a hard light, so that the shadow has a good sharp edge.

If you are shooting a scene and notice that there is a glare on a TV or computer screen, you can set up a flag just out of the shot, to create a shadow on the screen. Adjust the size of the flag by moving it towards and away from the computer. You can also turn it and twist it to conform to the shape of the screen. Dots can also be used to reduce or eliminate unwanted spectral highlights (bright reflections) from metal objects. Place a dot on a small arm connected to a light stand and cast its shadow on the bright spot.

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