Gobo Lighting

Gobo (lighting)

A gobo in a gobo holder, which goes in a stage lighting instrument. The discolored portion is oxidation of the stainless steel caused by the high temperature of the lamp, but the gobo is still usable.
A gobo is a template or pattern cut into a circular plate used to create patterns of projected light. The name may be derived from go between, or from Goes Before Optics. Go between refers to its position between the lamp and the lens. Another origin may be: Graphical optical blackout. Gobos are similar in use 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. Most ellipsoidal reflector spotlights (ERS) have moveable lenses to allow sharp or soft focusing.

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 theater, 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. In the UK, printer's Lithoplate was widely used as an inexpensive gobo substitute. However, these gobos tend to wear quickly due to the heat produced by a stage lighting instrument and are not viable for most venues.

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 lapse in the cooling apparatus, even for just a few seconds, can cause an expensive gobo to be ruined.

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.

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