A "strobe light" is a device that emits incredibly bright flashes of light, at a timed rate.
There are numerous haunt applications for a device that regularly flashes a bright light. Uses include: flashing at people to disorient them ("dot" rooms), slowing or stopping repetetive motion, startle lights, and simulating lightning.
There are various different kinds of strobe lights. Or perhaps there's a really good definition out there, and some of the products are misnamed. I have seen the following called "strobes":
Xenon flash lamps are frequently used for strobes, but other things can serve as well. Some old turntables use a tiny NE-2 neon tube as a strobe to help set the rate or rotation.
Strobe circuits are based on high voltages. This is true of even battery-operated units. It is extremely important to exercise appropriate cautions around this type of equipment to avoid electric shock. You don't have to be a rocket scientist, like my wife, but you do need to be careful!
All strobe units must have their electronics fully enclosed in an insulating case. The xenon strobe lamp must have a cover, in case it shatters during operation. When you purchase a ready-to-use strobe, it should come with these features. Don't open the case - it's dangerous in there!
If you build a strobe, from scratch or a kit, you must make it fully enclosed in an insulating case. The xenon strobe lamp must have a cover, in case it shatters during operation.
People with a particular type of epilepsy (photosensitive epileptics) can have seizures triggered by strobe lights. Strobes are not unique in this respect - any repetetive visual pattern can do it, from flashing video screens to sunlight twinkling off a mountain stream. The color of the light or visual pattern does not matter. The repetition rate does matter - the range of 5-30 repetitions per second is particularly sensitive. Strobes have a reputation for inducing seizures only because they are a relatively common source of precisely timed visual stimulation. If you are not already a photosentitive epileptic, exposure to strobes will not cause seizures. But if you are an undiagnosed photosentitive epileptic, exposure to strobes might cause a seizure. Most haunters accommodate this situation by putting up a sign simply stating that strobes are in use, letting the patrons decide for themselves whether they want to take the risk - photosensitive epileptics usually already know who they are.
There is a good article on photosensitive epilepsy on the web site of Birket Engineering, Inc.
http://www.birket.com
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In the United States, section 508 of the Rehabilitation Act of 1973 sets standards for accessibility of electronic and information technology. One part of the standards states:
Software shall not use flashing or blinking text, objects, or other elements having a flash or blink frequency greater than 2 Hz and lower than 55 Hz.Peak sensitivity is between 15 and 25 hz. The larger the size of the flashing area, and the higher the intensity of the flashing, the greater the chance of triggering a seizure.
There are additional risks posed by the use of strobes. The light is very bright - dazzling. When combined with motion or other visual effects, at can be disorienting. The resulting mental confusion can be used to advantage in a haunt, but in some places might prove dangerous, such as stairways.
Looking straight into a strobe for long periods might injure your eyes. If you are using high-power strobes in a haunt, you might want to bounce the light off of some light-colored surface instead of aiming the strobe straight at patrons.
Incandescent lamps use electricity to heat up a metal wire (filament) until it glows white-hot (black-body radiation). This heating and cooling process is not instantaneous, due to the heat capacity of the filament. In other words, an incandescent lamp is not capable of flashing very rapidly or of making flashes that crisply turn on and off.
But there is an alternative: the strobe light.
A strobe light is an interesting beast, producing light by a means utterly unlike the hot filament wire in an incandescent light bulb. A strobe light stores up energy in an electrical component called a "capacitor", and then suddenly dumps it all into a lamp bulb filled with xenon gas. The normally insulating gas in the bulb suddenly conducts electricity. This produces a sudden, brief, and intense flash of light.
WARNING — Strobe light circuits can be very dangerous to work with, because they store up a large amount of energy in a capacitor and can release it all at once. If you purchase any kind of flash unit prebuilt, don’t open the case - there are potentially lethal voltages inside. Just use it. If it breaks, take it to a qualified repair facility. Even unplugged and turned off, these units can be lethal! Every strobe light should have a transparent cover over the lamp.
Whether you know it or not, you have probably seen hundreds of strobes before, in the form of flash units on cameras. The following schematic approximates the electrical contents of a Kodak Funsaver disposable camera.
The circuit is composed of four areas: an inverter to generate high voltage, the energy storage capacitor, a triggering mechanism, and the actual flash lamp. We will soon examine exactly how it works.
This particular circuit contains two gas discharge tubes. Understanding how they function is the key to operation of a strobe light, and how they might be useful to the haunter.
We will start with a discussion of the common NE-2 neon lamp. This is a small tube that has two leads that go through the bottom of the glass envelope and attach to metal electrodes inside the lamp. The neon gas that separates the electrodes within the tube makes a poor conductor of electricity. You could try all day to pass 75 volts through the NE-2 and it would act like an insulator. But if you crank the voltage up high enough, the gas ionizes and suddenly turns into a good conductor of electricity. This is called the "turn-on threshold" voltage, and is roughly 90 volts for a NE-2. We would see that as an orange glow in the tube, and a meter would indicate that there is plenty of electricity flowing through what was formerly an insulator.
Once the tube fires up, it continues being conductive, even if the voltage is reduced below the turn-on voltage. When you drop to about 60 volts, the NE-2 goes out. This is the turn-off threshold. In order to start it up again, you must get back up to the turn-on threshold. This is an example of the phenomenon called hysteresis.
The flash circuit uses a miniature neon lamp, similar to the NE-2, for the "ready" light. The lamp is actually about half the size of a NE-2 and has a higher turn-on threshold of roughly 180V.
The other gas discharge tube in the circuit is the flash lamp. It is a thin cylinder 22 mm long, filled with xenon gas instead of neon gas. The electrodes exit at opposite ends of the tube. Like the other gas discharge tubes that we have discussed, the xenon lamp has a threshold at which it will suddenly begin to conduct electricity, but the turn-on threshold is even higher for the xenon flash lamp. Just like the neon lamp, it acts like an insulator until you hit the threshold, then it ionizes and conducts well, even at a subsequently reduced voltage. The nice thing about the xenon tube, however, is that it makes a nice white light that is well suited for photography - or lightning.
If you so desired, you could make a flash unit that worked by accumulating energy in a storage capacitor until the turn-on threshold voltage of the xenon lamp is reached. It would then fire, producing all of that nice light. This is a bit of a problem because it takes awhile to generate a high enough voltage to fire the lamp and store enough energy in the capacitor to make the flash long enough to be useful. So you might press the shutter release on your camera and a little while later, the threshold would be reached and the flash would go off, too late to do any good.
One could put a switch between the storage capacitor and the tube. The capacitor could then be charged in advance to well over the turn-on threshold of the flash lamp. Since this part of the preparation, it doesn’t matter that it takes a few seconds to build up this potential in the capacitor. Closing the switch would then fire the lamp. The problem with this approach is that a huge amount of energy must be switched. This requires a switch built and rated for large current spikes and high voltages (read "expensive switch").
Most photographic strobes use a bit of a trick. They put a voltage across the xenon tube that is lower than the turn-on threshold, but higher than the turn-off threshold. Nothing happens because the turn-on threshold has not been reached. Now, if only you could start the xenon tube conducting, it will continue to conduct and produce light. All it needs is a kick. This is done by introducing a third electrode to the tube, aptly called the trigger electrode. When the shutter is released, a high voltage pulse is applied to the trigger electrode. The pulse is high enough to start ionizing the tube, but doesn’t have enough oomph behind it to produce a usable quantity of light. But awhile ago, we set up a potential that was just waiting for somebody to give it a kick, and the flash lamp burns until it drains enough energy from the capacitor to make the potential across the xenon tube drop below the turn-off threshold.
Here's how the Kodak Funsaver circuit works:
The strobe from a disposable camera is designed to be cheap and reliable. It produces a single bright flash of light, when and where you need it - then requires several seconds to charge up again. Fancier units, for more expensive cameras, can provide brighter light, with a faster recharge time.
The strobe lights that escaped from the camera shops and sought refuge in discotheques are not triggered by camera shutters. Instead, they have a "repetition" control that tells the unit how frequently to flash. Once you set a strobe to, say 3 flashes a second and turn it on, the unit will emit bright short flashes, 3 per second, for hours on end.
Various electronic circuits are used to provide the repetitive trigger of a strobe light including: neon lamp relaxation oscillators; programmable Unijunction Transistors; and integrated timer chips, like the 555. Here is an example of a repeating strobe light based on a neon relaxation oscillator:
The light tends to be a very nice white or blue-white color. The combination of color, intensity, and brevity make xenon strobes look a lot like lightning flashes. In fact, one could argue that they actually are miniature lightning flashes, since lightning is itself a rapid gas discharge of energy stored in cloud capacitors!
The output power of a strobe is usually rated in "Watt-Seconds". This is sometimes incorrectly reported as "Watts". Most cheap strobes are 20 Watt-Seconds. 20 doesn't sound like much, but all of that energy is released at once, usually while you are in the dark, so it hits fairly hard.
It is more difficult to build a strobe that flashes rapidly than one that fires slowly. You have to worry about rapidly recharging the capacitors. You have to worry about the xenon tube getting hot. This amounts to a different technical design, and higher grade of components.
If a really fast flash rate is important to your application, expect to pay more for it. But for simple haunt applications, most standard strobes will work fine.
Almost all strobes allow you to set the rate of the flash, from slow to fast. But not all of them offer this feature. Strobes intended for photographic use don't even have a flash rate - they only fire once.
You won't find this on inexpensive units. High-end, higher-power units can be dimmed so that each flash is only a fraction of what it usually would be.
Two rules here: (a) the more remote controls, the costlier (b) digital remote costs more than analog.
Starting at the first rule, the ideal strobe allows you to remotely control anything that you can control via a local knob on the strobe. Thus a strobe with a knob for flash rate and intensity would also allow remote control of both these features.
According to the second rule, the cheapest form of remote control is an analog signal, such as a DC voltage on a 1/4-inch jack. The most flexible (and costly) is remote control via DMX.
Watch out for high-power strobes that require 220. Most haunts aren't wired with it!
Also check the number of Amps drawn by the strobe, if it is a large unit.
You will probably want a strobe that is U.L. listed. Ultra-cheap units might not be. Check the box before you buy it.
Most strobes dump all their energy instantly, providing a very short, but very bright flash. Strobes at the high end can spread out the emission for a longer flash. Strobes that can do this are quite expensive.
Price varies a lot, but isn't always an indication of what you are getting. As an example, a typical low-end strobe is a 20 Watt-Second unit with 110 VAC input, variable-rate, and a short linear tube. I have seen these for sale at prices ranging from $5 through $40, $20 being quite common. Although the circuitry inside may be different, they share all the same essential features. Why pay for the costly version of the same thing?
At the same time, additional features, like high power and DMX, must cost more money.
It's just that paying a high price isn't a guarantee that you are getting more. You have to pay close attention to the features that you are getting.
25W mini strobe light; compact; variable speed knob to adjust strobe flash rate; plastic casing. Dimensions: 2" H x 3.25" L x 5", weight: 1 lb.
Power requirements: 120V.
List Price $27.
750W; flash rate from 1 to 15 flashes per second; rear speed control knob. Dimensions: 13" x 11" x 6"; weight: 7 lbs.
Remote control via DMX for rate and brightness; 0-10V signal for speed.
Power requirements: 120V.
List Price $350.
200 joules/flash, 36,000 Watts Peak flash. Air cooled with auto fan control. 5 ultrabright Hyperflash effect emission modes including lightning and continuous illumination. 3 operation modes including normal (rate and intensity), single flash and Hyperflash (5 effects emission modes) in both DMX and analog.
Remote control: DMX; 0-10 volt analog inputs/outputs.
Power requirements: 240 Volt 50/60Hz operation; 1 fixture per 30Amp circuit.
It looks like 2000 was the year of the cheap strobe lights. Near Halloween, you could buy them at WalMart for $15. My theory is that "China, Incorporated" geared up to make strobes. And whatever they make in quantity, sells in the U.S. for cheap.
And, honestly, if you built from scratch a comparable strobe, it would cost twice that! And that's not even counting your labor!
My point is simply this... Electronics is a fascinating hobby. It can be fun. It can be educational. But if you want an existing product at the best possible price, find out who is commercially manufacturing them in quantity. And buy one from them.
Why does it cost more to build one yourself?
You buy the tube (markup), the storage caps (markup), switch and pot (markup), assorted minor
components (markup), the case to put it in (markup), bulb shield (markup), power cord and fuse (markup),
board to build it on (markup).
And what's the labor cost? You need to lay out and assemble the unit; drill and cut the project box to fit;
put it all together; and you must have run all over town to find the parts.
When you are done, your unit lacks U.L. certification and a warranty.
Just about the only valid excuse for building something like this yourself is that you are willing to
pay more in order to learn about the innards of a strobe, or you want something different from the
commercial units - something you can't buy.
There is a halfway approach: buy a kit and build that.
The kit vendor has already done the engineering and the shopping for you.
He bought his parts in quantity (for cheaper than you could).
And since his parts cost less, the markup on the kit is probably a little less than on
parts you would buy yourself.
Of course, you still have issues with U.L. certification and warranty.
And many kits come without a case.
For other projects, a case is optional - but for a strobe a case and proper shield over the
bulb is mandatory!
For simplicity, we will assume that all parts come from
Radio Shack.
[You can get better prices if you shop around (costs gas money) and/or order parts by mail (costs postage).]
Prices are as of 10/2004.
Can I build one myself for cheaper?
Probably not!
Running The Numbers On Cost
Don't believe that it costs more to build one yourself?
Let's estimate what it would take to throw together the "classic"
simple strobe light diagrammed above.
| RS part number description
| price
| comment
| |
| 272-1145 | Long-Life Strobe Tube | $3.99 | |
| 900-8751 | 4kV Trigger Coil | $0.99 | |
| none | SCR | ~$1.50 | wild guess; RS sells power transistors at about this price |
| none | ne-2 neon lamp | ~$.50 | wild guess |
| 276-1104 | 1N4005 diode | 2x $0.89 | this is a usable substitute |
| none | 500k potentiometer | $2.89 | estimate; RS 5k pot 271-1714 sells for this |
| none | 330ohm 5W resistor | $1.79 | estimate; RS sells power resistor 271-135 for this |
| none | mylar capacitor | $.50 | wild guess |
| none | 1/4W resistor | $.99 | estimate; RS sells resistor 271-1301 for this |
| none | electrolytic capacitor | 2 x $1.29 | estimate; RS sells electrolytic capacitor 272-1017 for this |
You can also get some very similar kits. These kits tend to include cord and board, but not include case, knob, and fuse. So we would need perhaps $8 worth of parts to finish those.
At the time of this writing, the Halloween department of Wal-Mart sells two strobes from Lite F/X. The small strobe sells for $9.99. The larger strobe (closer to the one we are estimating) sells for $14.99.
So, let's compare the result:
route
| base cost
| added bits
| final cost
| |
| build from scratch | $17.51 | $10.00 | $27.51 |
| Velleman #K5300 kit | $15.96 | $8.00 | $23.96 |
| Graymark #G104 kit | $12.55 | $8.00 | $20.55 |
| Chaney Electronics #C4823 kit | $18.25 | $8.00 | $26.25 |
| Lite F/X from Wal-Mart | $14.99 | $0 | $14.99 |
Any questions?
Technically, there is no good reason to measure a strobe in Watts.
Anybody who writes "25 Watts" on the box is a bit nutty.
The energy released by a strobe is not measured in Watts, but in measured in Watt-Seconds (WS),
also called Joules.
Perhaps they are quoting this figure, but incorrectly marking it "Watts" instead of "Watt-Seconds".
The power consumed from the line may be measured in Watts, but is probably a peak figure and
has little relationship to the light output.
Let's assume they really mean "Watt-Seconds". Light bulbs are measured in Watts.
This tempts you to compare "I have a 100W lamp in the living room, so
a 25WS strobe won't be too bright."
First, you have to compare apples to apples.
Imagine if you had the ability to capture all the light emitted by that 100W lamp for a second.
Gather all that light in a box. That's 100WS. Now, take a quarter of that (25WS). That's what
the strobe puts out. So you think it's going to be dimmer.
But it took the ordinary light bulb a full second to put out all that light.
And the strobe light dumped out all that light in the short duration of a single
flash (say 1/100 second).
So the strobe put out 1/4 of the energy in 1/100 of the time.
That makes the light from the strobe 25 times more intense than the living room lamp.
Now, we add a few more factors: a xenon lamp is much more efficient than an incandescent
lamp, so more of the strobe's energy shows up as light.
And you usually flash strobes in dark or dimly-lit rooms, where the eyes aren't expecting much
light anyway.
Overall, that cheap strobe, confusingly marked "25W", may be just what you need.
So, try it out under the conditions in which it will be used, and see for yourself.
Thank you for visiting. Your comments are welcome.
25 Watts doesn't sound very bright
With strobe lights, you pay more for more power.
Inexpensive strobes are often marked "20 Watts" or "25 Watts", which
causes some purchasers to remark "25 Watts doesn't sound like very much."
They're wrong - the strobe could be just right!
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