The profile-spotlight, which is one of the most common types of theatre luminaires, can be used to project simple contour patterns. A gobo (also called template or  cookie), which is a cut out metal slide, is inserted into the gate of the profile-spot. Celluloid slides cannot be used as the temperature of the gate is very high and only a hardy metal can survive the heat. Gobos were first used in the 1950's by cinematographers. Theatre lighting designers like David Hersey of England and Jules Fisher of the U.S.A. began to explore the potential of gobos to create shapes and textured light, and it quickly became a popular effect used in theatres all over the world.

A gobo can be used to recreate light patterns and textures for projection on any surface: sets, floors, and actors. Gobos can also be used to great effect in conjunction with color filters. In certain luminaires, the gobo can be rotated using a rotator attachment with a motor which allows variable speed rotation, and many types of intelligent luminaires feature specially designed rotating gobos. Gobos are, on occasion, used for effects of lightning, snow, water or a moon or sun .

Gobos are affordable even to the humblest theatre and are available from most lighting equipment suppliers who will supply both off-the-shelf, as well as custom-made, gobos in various shapes and forms. Simple gobos can be produced in-house by cutting zinc-tin plates or aluminum foil.

Rosco's VORTEX 360 Dual Rotator placed in Strand SL series spotlights

Rosco's Indexing Rotators - Double and Single Gobo Rotators

A variety of gobos

Gobos have certain limitations. The cutout shapes must be connected by pieces of metal, and the quality of the projection deteriorates with time as the gobo becomes warped from the heat. The more intricate a shape, the more chance there is of this happening.

Glass Gobos
A gobo may be made from borosilicate glass with a metal thin film coating, allowing more complex designpup.
Glass gobos can include colored areas (much like stained glass windows on a small scale), made of multiple layers of dichroic glass, one for each color glued on an aluminium or chrome coated black and white gobo. New technologies have made it possible to turn a color photo into a glass gobo.