Gobo (lighting)

A gobo or GOBO (short for Graphical optical blackout) is a physical stencil or template that is placed inside or in front of a light source, to control the shape of the emitted light. They are often used with stage lighting instruments to manipulate the shape of the light which is cast over a space or object. A metal gobo with patterned holes allows only the desired shape or pattern of light through, casting a specific pattern of light and shadow into the space.

Though the term "gobo" has come to generally refer to any device which produces patterns of light and shadow, and various pieces of equipment that go before a light (such as a gobo arm or gobo head), in theatrical lighting applications the term more specifically refers to a device placed in 'the gate' or at the 'point of focus' between the light source and the lenses (or other optics). This placement is important because it allows a pattern with crisp, sharp edges to be projected (for logos, fine detail, architecture, etc.). Gobos placed after the optics do not have the option of such fine focus, and are more precisely called "flags" or "cucoloris" ("cookies").

Gobos may be used, in connection with projectors and simpler light sources, to create lighting scenes in a theatrical application. Simple gobos, incorporated into automated lighting systems, are popular at nightclubs and other musical venues to create moving shapes. Gobos may also be used for architectural lighting, as well as in interior design, as in projecting a company logo on a wall or other feature.

Gobos can be made from various materials. Common types include steel, glass and plastic/transparency gobos.

Steel gobos use a metal template from which the image is cut out of. These types of gobos are the most sturdy of the common gobo types but often require modifications to the original design called bridging in order to display correctly. In order to correctly represent the letter "O" for example, small tabs or bridges must be made in order to keep the metal tab in the middle of the letter supported. This effect may be undesirable in more intricate patterns or designs.

Glass gobos are made from transparent glass with a partial mirror coating to block the light and produce "black" areas in the projected image. This eliminates any need for bridging, since the glass itself is the support, and allows more intricate images to be produced. Glass gobos can also include colored areas (much like stained glass windows), whether by multiple layers of dichroic glass (one for each color) glued on an aluminium or chrome coated black and white gobo, or by newer technologies that allow the thickness of the dichroic coating (and therefore the color) to be varied in a controlled way on a single piece of glass, making it possible to turn a color photo into a glass gobo. Glass gobos generally offer the highest image fidelity but are the most fragile.

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Wikipedia