Back to Home Back to Lightning About the real thing
There are a lot of ways of creating an illusion of lightning on stage: Strobes, Tesla Coils, Neon tubes, etc. The best way to produce a convincing illusion of lightning on stage is not to use an illusion at all, but to use the real thing: a real bolt of lightning. Using technology developed for testing military and commercial power line equipment, we can produce artificial lightning on cue.
We create a real lightning bolt: a very fast high voltage pulse of tens of thousands of amps, producing an arc column about an inch in diameter, a very bright light, and a very loud noise. This is real lightning.
This is not the Tesla coil type displays you may have seen before. Tesla coils produce high voltages but at relatively low currents (measured in fractions of an amp). You typically get a brush of thin sparks with the usual crackling noises. Tesla coils can be used to generate 20-30 foot long sparks, however, there are some practical problems at these sizes, and it doesn't look like lightning anyway.
So how do we make lightning? There are several techniques we can use. The brute force approach is to generate a multi million volt pulse of electricity, which will jump from the electrode to whatever is nearest, hopefully another electrode. A million volts will reliably jump about 5-6 feet through the open air, with the distance proportional to voltage. Other objects would need to be a minimum of 20 feet away from the electrodes to prevent inadvertent side flashes which would damage equipment. The Deutsches Museum in Munich, Germany has a nice high voltage show which illustrates this technique nicely.
A better way, which we use to make the lightning safe and controllable, is to pre-rig a fine wire (invisible from more than 10 feet away) between the electrodes. A high energy electrical pulse vaporizes the wire (it actually explodes) and an electrical arc follows the path of the wire. Since there is a wire already there, we don't need as high a voltage to jump the gap. A single wire spanning 40 feet can be exploded with very high voltages near a megavolt (1,000,000 volts). With more reasonable voltages and powers, the wire segments are 6-10 feet long. To create longer lightning bolts, or for creating jagged forks, we arrange a series of wires, and fire them simultaneously or in quick succession. For multiple strokes, you can rig multiple wires, and switch between them during the show. Different types of wire can be used to produce colored arcs: red, yellow, green, blue, etc.
Although this technique is much safer and more controllable than giant Tesla coils or multi-megavolt pulsers, it still requires some careful planning and installation. It is not suitable for a continuously changing show. However, in a permanent installation or for a travelling show which is fundamentally identical in each venue, the engineering and design time would only be required once.
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The basic approach we use is similar to an electronic camera flash or strobe. We gradually store electrical energy in a capacitor, and then dump it all at once into the wire. Of course, in a strobe, the voltages are typically less than 1000 volts (1 kilovolt). In our exploding wires, we start at 10,000 volts for short wires, and go up from there. The peak power during the lightning bolt may be a billion watts, but it lasts much less than a thousandth of a second.
The equipment required to do this consists of a high energy discharge capacitor, high current trigger switches and a variety of other components (safety dumps, timing controllers). The whole assembly is called an Energy Discharge Unit, and is about a cubic meter and will weigh several hundred pounds. Higher voltages require bigger and heavier capacitor units. Special high voltage cables connect from the capacitor to the exploding wire attachment points. These cables are comparable to welding cables in size and weight. The following drawing shows an example arrangement on stage with the wires hung from a lighting truss and the energy discharge units offstage on the side.
A dual redundant control system is responsible for controlling the energy discharge units, the charging supplies, and triggering the discharges when required. The entire system is designed to fail-safe, so that if one or more components fail, no hazards can exist.
Natural lightning is often forked, and the bolt appears to travel from one end to the other. We do this by using a series of wire segments that are exploded in sequence. The following diagram shows an arrangement with 3 segments and their associated equipment. The insulating standoffs are plastic or ceramic posts that hold the wire in position. The drawing isn't to scale, so the wire segments can be quite close to each other (a few inches, typically) and will look visually continuous from any reasonable distance. There isn't any real limit on the number of bends in each segment, nor on the number of segments (except for the cost of the hardware, of course).
The visual effect is quite impressive, creating a forked bolt of lightning that appears to progress as you trigger each wire in sequence. The following diagram illustrates this overall effect. Of course, for multiple bolts in a show, you rig parallel wires, and fire them as appropriate.
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The precise system necessary for a desired effect will require custom design, however, here are some design guidelines to help you determine how to make the lightning work for you. The following paragraphs describe some of the design parameters that we work within when designing your system.
If possible, you should strive for each explosive wire leg being 4-10 feet long. This length will provide the best effect while keeping voltages down, which makes safety easier. The legs do not have to be straight lines. Insulating support posts made of plastic are used at the bends and can be made in a variety of colors, although they cannot be painted. The exploding wires should be at least 2 feet away from any other metallic objects, including things painted with aluminum paint, lighting instruments, trussing, etc. The precise distance will depend on the voltage levels being used and details of the objects. Closer spacing is possible with careful design.
Consider where you will want to place the energy discharge units. The distance from each exploding leg to its corresponding energy discharge unit should be minimized. Longer lead wires reduce the maximum leg length and require higher voltages, which costs more. For instance, if the lightning is arranged on a set piece or backdrop, the energy discharge units could be supported behind the drop near the wire span. A truss based system might mount the energy discharge units on the truss.
The exploding wires cannot touch each other, and must be separated by several inches if they cross. Exact minimum spacings are installation dependent. You can put a number of wires parallel to each other, several inches apart. This is handy for doing multiple bolts in sequence, or for rigging a whole day's worth of shows at one time. The energy discharge unit will be designed with multiple outputs to connect each wire in turn.
The time between firing successive wires from the same energy discharge unit mostly depends on how much electrical power you can supply. Recycle times range from 60 seconds to about a second. The faster you recycle, the more electrical power you draw, and the bigger (more expensive) the charging supplies are. Recycle times faster than 1 second will require significantly more complex system design. If you need to fire a bunch of bolts in quick succession (e.g. fractions of a second to a few seconds between bolts), you are better off planning for multiple energy discharge units.
Water and electricty is a tricky combination, particularly at the voltage levels we use for the lightning. If you need to have a rain storm with lightning, consider spacing the rain from the lightning, say by having the rain in the foreground, and the lightning behind it separated by a good distance. However, with special design and much more complex insulation, you can actually fire the lighting in a rain storm. For example, electric utilities build high voltage power transmission towers which run at several hundred thousand volts in the rain without too many problems.
The lightning bolts create an intense electromagnetic pulse (just like the real thing), which will potentially disrupt radio communications or other electronic equipment that is close to it. Properly shielded electronic equipment (e.g. that which has FCC certification), will probably not be affected. Radio communications might get a “pop”, although this is highly idiosyncratic, and you might not hear it over the “bang” from the discharge. In any system design, we will address these concerns.
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The costs for this effect can be divided into 3 basic areas: (1) Design and Development - including any testing necessary to develop the precise effect; (2) Initial Equipment - The high voltage componentry, fixturing, etc; and (3) Operating Costs - which can be divided into Expendables (e.g. the wires that explode) and Equipment Replacement. While there is a significant initial investment for a system, the operating cost is quite low, particularly compared with pyrotechnics. As a rough estimate, the direct operating cost (excluding electrical power, manpower, etc.) for expendables and equipment replacement is a few dollars per shot.
Two things are consumed in each shot: the exploding wires get vaporized and need to be replaced, and, the high voltage switches use an dry nitrogen as an insulator which is replaced after every shot. Wire costs are pennies a shot and about a cubic foot of nitrogen is used in each shot, also at pennies a shot.
The high energy discharge components used in these systems have finite lives, typically specified as a number of “shots”. A typical component will have a life of 10,000 to 100,000 shots, depending on design parameters, which would take into account the replacement costs of the component and the labor costs to do the replacement.
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This effect is comparable to real lightning in its potential hazards. There is a lot of energy like lightning, a very bright light like lightning, and a very loud noise just like lightning. In fact, it is deadly just like lightning; if it hits you, you will be dead. The safety of this effect is of paramount concern, and is addressed from three standpoints: operator, performers & crew, and audience. A signficant amount of the system design time is devoted to safety, since the basic technology of exploding wires and arcs is relatively well understood, particularly for an application like this, where the actual details of the wire vaporization and followthrough arc are not critical.
Primarily, this is concerned with insuring that the operator doesn't get electrocuted when rigging or setting up the effects. Proper grounding switches, energy dump relays, and similar devices are necessary to insure that the exposed parts of the system are at ground potential when anyone is working on them. Extensive training, as well as hiring people who have the necessary background and knowledge, is also essential. Mechanical and electrical interlocks also provide some safety. However, they can be circumvented; ultimately, you have to rely on good procedures and well trained operators. The operator is also responsible for insuring that the effect isn't triggered when it would create a hazard.
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The exploding wire effect requires safety precautions similar to those already familiar to show designers. Current shows use high power lasers and pyro effects which require appropriate consideration as to safe distances, aiming of lasers, and so forth. Some education of the show designer as to the peculiarities of this effect will be necessary.
The exploding wire will create extremely high peak sound pressure levels (SPL's). Existing shows already run at sustained high SPL's (>140dB), and have very high impulse peaks. For example, theatrical maroons produce high peak SPL's similar to those from an exploding wire.
One novel hazard which will need to be addressed is the intense UV radiation from the arc. We can control this to some extent by choosing appropriate waveforms (and hence the plasma temperature and size). Depending on how the show is designed, the performers may need to wear sunscreen and protective eyewear or appropriate shielding would be installed(transparent UV blocking curtains) . In any case, the hazards are similar to those created by arc welding operations.
The other novel hazard is the presence of fairly high voltages at specific times during the effect. By segmenting the wire and firing the segments separately, we can keep the voltages down. After that, it is an issue of determining appropriate safety distances and procedures, much as is done currently for pyro effects.
The issues here are similar to those with the safety of the performers and crew, with two significant differences. First, the audience is farther away than the performers and crew, so some of the effects are reduced as the square of the distance. Second, the audience won't be wearing sunscreen or protective eyewear, and cannot be assumed to take any particular precautions. The high peak SPL will probably comparable to existing effects. We envision that something like transparent, UV blocking curtains would provide any necessary UV filtering.
The exploding wire effect will be potentially hazardous. However, the level of hazard is comparable to existing theatrical effects using pyrotechnics. We would like to make a distinction between this electrical effect and pyrotechnics, since although similar precautions are necessary, e.g. shielding, safe distances, trained operators, there are distinct differences. A licensed pyro technician probably would not be the optimum person to operate this effect, and in any event, we would like to avoid the regulatory issues that surround the manufacture and use of pyrotechnics. We expect to develop appropriate selection criteria for potential operators, and train them extensively. This effect is unique, as are its hazards, however, the uniqueness is what makes it desirable.
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Comparing ours to the real thing. (Background on natural lightning)
A typical lightning flash is composed of 2-4 visible strokes spread over a couple of tenths of a second, which is what gives you the “flickery” effect. Each stroke is preceded by a faint leader which establishes the path for the actual visible stroke to follow. The actual path isn't straight, but is a series of 50 meter long straight segments that are connected together. It takes about 60 millionths of a second for the return stroke to follow the channel established by the leader. In a few millionths of second, the air is heated to about 20,000 degrees Celsius, causing it to expand very quickly and forming a shock wave, which eventually turns into thunder. The long duration rumble of thunder is caused by the sound from different parts of the stroke (which is typically 5 km long, although you only usually hear the sound from the lower 1000 meters) arriving at different times. If you are really close to the lightning, all you hear is an incredibly loud bang or crack. The energy in a stroke is about 100,000 Joules per meter, or 300 million joules for the whole stroke.
If you are looking to duplicate the look of real lightning, you need to think about the proper scale. Scaling a 3000 meter long flash down to 10 meters means that the little jagged segments are going to be about 20 cm long. There are typically a half dozen or so branches, which would be about every 2 meters in a scaled version. More significantly, the apparent brightness of a scale lightning flash would be about 100,000 times less than the real thing, requiring about 3000 joules (watt seconds) to produce a comparable intensity of the flash.
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Copyright 1997, Jim Lux / Back to home page / Mail to Jim
