A variety of fire effects are available, depending on your needs and how realistic you want the effect to appear. Simple fireplace or torch effects are available at party supply shops and department stores, if you want a bit of fake flame for your party or special event. For larger events such as theatrical productions, you can rent fire effect units that simulate the appearance of moving flames.
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You can create the look of a live torch or cozy fireplace without the dangers of real fire by using an LED-based fire fan. These units generally have several bits of silk or other semitranslucent cloth cut into rough flame shapes. Red and orange LED lights illuminate the fabric, while a gentle fan blows the pieces to create the look of moving flames. The most realistic versions of these effects also include a blue LED near the center of the fire, which helps create a more realistic color for the false flames. You can make your own fire effect by examining the commercial variety, but make sure you use LEDs rather than incandescent light bulbs, as LEDs do not create much heat, while incandescent bulbs may get hot enough to turn the fabric flames into real fire.
Most special effects units that project moving flames use steel patterns called "Gobos." The special effects unit is attached to a standard theatrical lighting instrument (the proper term for a stage light). One method of creating this look is to use a gobo in a basic flame shape set into the lighting instrument's standard gobo slot. Choose a second gobo with a different pattern -- anything with several fine lines in an irregular pattern will work -- and place that in a gobo rotator, which is a simple, relatively inexpensive special effect unit. When the light is focused so the stationary flame pattern is semisharp and the spinning gobo is soft-edged, the spinning motion creates the look of flickering and movement in the flame. Add an orange gel (color filter) to your light and you'll have a fire effect. Scrolling effect units that use patterns made of steel loops cut into flame shapes are also available for a similar effect.
If all you need from your fire effect is the look of firelight, not the flame itself, your job is simple. Place any lighting instrument bright enough for your purposes at a low angle, such as on the floor at the front of the area you are lighting, or inside a false fireplace, and add an orange gel to the light. Attach the light to a lighting console or any other programmable controller and set the controller to flicker it to at least five various levels -- including off -- in a random pattern. For example, set your controller to give the light power at 0 percent (off), 30 percent, 60 percent, 75 percent and 100 percent, continuously changing from one to the next in random order. If your controller will randomize the speed, set it to do that as well. Keep adjusting the speed and levels until you achieve the look you want. A slower flicker will create a warm, cozy firelight look, while a faster flicker can simulate out-of-control flames.