Thursday, January 15, 2009

Use Gobos to Design With Light

Lighting in schools and classrooms is usually pretty boring and unattractive. An easy way to add color and pattern to a dull room is by modulating the light. Gobos (left) and Cookies (right) are devices used in theatre to provide interesting lighting designs. A gobo is a template or pattern cut into a circular plate used to create patterns of projected light. Gobos are attached to the lighting fixture while cookies are placed between the lighting fixture and the area to be lit (as in the picture on the right taken during the filming of the movie "National Treasure".

Gobos are similar to cookies (see cucoloris), and flags, which are placed farther from the lighting instrument between the lens and subject. Gobos control light by blocking, coloring, or diffusing some portion of the beam before it reaches the lens. Because the light is shaped before it is focused, hard edged images can be projected over short distances.

A theatrical gobo may be made from either sheet metal or borosilicate glass, depending upon the complexity of the design.
Glass gobos can include colored areas (much like stained glass windows), made of multiple layers of dichroic glass, one for each color glued on an aluminium or chrome coated black and white gobo. New technologies make it possible to turn a color photo into a glass gobo.

In low budget applications, discarded soda cans or pie plates can be used and patterns cut out with any cutting tool. The latest commercial technology enables finely dithered patterns which give the illusion of shading.

Plastic gobos—which are generally custom made—are available when a pattern is needed in color and glass does not suffice. However, these thin plastic films generally need to be used with special cooling elements to prevent melting them.

A number of simple and complex stock patterns are manufactured and sold by various theatrical and photographic supply companies, or custom gobos from customer-created images can be manufactured for an additional fee. Generally the lighting designer chooses a pattern from a catalogue or small swatch book provided by the manufacturer. Because of the large number of gobos available, they are generally referred to by number, not name. For example, most manufacturers offer a gobo of a window, but they are all slightly different. So instead of calling it window, it would be identified as gobo 77143.

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