Strobe lights use stroboscopic lamps to produce regular pulses of light, each one similar to the flash on a camera. These pulses can be controlled for whatever speed the director wishes. The strobes are used for a number of atmospheric effects in theater, including providing the illusion of actors moving in slow motion. Strobe lights are also used to accomplish many supernatural effects.
Gobos are metal discs inserted in front of stage lights. Patterns are cut out of these discs, blocking light in some areas and allowing it to pass in others. The result is that these patterns are projected onto the stage. Some gobos have specific and recognizable shapes such as geometric symbols or animal outlines, while others are more abstract and can be used for a number of effects.
Gobos are sometimes attached to a revolving wheel in front of its light source, giving the illusion of moving clouds, mist, fire and other effects onstage.
Fog machines similar to those used at Halloween (though more powerful) are often used to create smoke and fog effects in theater. These pass a special fluid over a heating element, which vaporizes it. The vapor is pumped out of a nozzle on the end of the machine. There are two types of fog fluid that can be used: short term, which creates fog that lasts only a few minutes; and long term, which lasts up to 30 minutes.
In addition, dry ice is often used to create fog that must cling to the floor. It is a frozen, solid form of carbon dioxide and has gasses that are heavier than air. When chunks of dry ice are put in hot water, it sublimates (turns directly from a solid to a gas) and spreads out to cover the surrounding area before dissipating.
Flash pots allow the safe execution of fire, smoke, sparks and explosions onstage. Also used in rock concerts and professional wrestling, these metal containers are filled with specific amounts of chemicals that are ignited electronically with the push of a button. Flash pots are among the most dangerous of theatrical special effects and should only be used by a trained professional.