Magazine article American Cinematographer

Specular Transparency: Controlling the Primary Highlight

Magazine article American Cinematographer

Specular Transparency: Controlling the Primary Highlight

Article excerpt

A recent production for a Buick California Regal television involved photographing a car on a black, covered stage. The plan for lighting the shoot was to illuminate the car with a single, large overhead light source, and to light the black background wall with HMI Pars. The daylight-balanced Pars would produce a blue glow that would provide separation between the car and the background. Beyond a few minor choices regarding separation lights, the most important lighting decision to be made was the method in which the car was to be lighted.

There are an infinite number of ways to light almost any subject, and the tools that we choose in a large part help to define the individual styles of each imagemaker. But there are subjects, especially in product-based commercials, that do require the use of certain tools to define their particular characteristics. For automobile commercials, shape and color are very important characteristics that need to be accurately conveyed. Surface texture, or shine, also requires a great deal of attention. It is the specular highlight (the mirrored image of the light source) that helps us to define on film both the shape and the surface texture of a product. This article is not so much an illustration of how to light a car, for there are many ingenious ways to light cars, but more an effort to determine the controis and effects of the large, primary light source used to illuminate them.

Specular transparency is a term that I use to describe the level of translucence of the specular highlight. A highlight with a high level of transparency would be one which allows you to see into the highlight, or which reveals a great deal of detail in the highlight area. Low specular transparency would be a highlight area that reveals no product detail, such as car color, or a highlight considered to be white without detail. To understand how to manipulate the transparency of the primary highlight area, we must first understand the controls that affect the specular highlight.

Because the specular highlight is a mirrored image of the light source, its size, position and brightness are all directly related to the size and relative position of the light source to the subject. The larger the light source, the larger the specular highlight. The closer the light source is placed to the subject area, the larger the specular highlight. The Inverse Square Law states that light from a point source increases or decreases inversely to the square of the distance moved. (The theory is accurate for intensity of light with raw, unaffected light only, as reflectors, lenses and diffusion will affect the rate of fall-off.) This means that if you move a light source from 10 feet to 20 feet away from the subject (twice the distance), the light will diminish to ¼ of its original intensity. Moving it from 10 feet to 5 feet, on the other hand, will quadruple the intensity. Of course, the starting point for all of these measured values is a random factor.

The same is true of the size of the light source and the specular highlight; if you move your source twice as close, the effective size of the source and the highlight will increase by a factor of 4. If a source is moved 4 times the distance away from the subject area, the source effectively becomes 1/16 the size. As you can see by this explanation, moving a large source away from the subject will diminish its effective size rapidly. If the source must be set at a great distance relative to the product, the light source must be enormous in size and intensity to compensate for the distance and maintain the same lighting effect.

Cars are often shot under the open sky at day's end, or magic hour; in such situations, the entire sky acts as a large, spherical silk over the car. Relative to the size of the car, the sky is extremely large and fairly close to the product, so it coats the car in a wonderful highlight that reveals shape and texture to the viewer. …

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