|This is the talk page for discussing improvements to the Flashtube article.|
- 1 Animated GIF image
- 2 Spectrum
- 3 Minimum operating voltage
- 4 Xenon flash lamp in Color Spectropphotometers
- 5 Technical error
- 6 Discharge Lamp?
- 7 Operation Section is a bit confusing
- 8 Construction section
- 9 Intensity and Duration needs rework
- 10 Changes have been implemented
- 11 Vraiable Pulse Width Control triggering
- 12 Other gasses and safety
- 13 Requested moves: Xenon Flash Lamp to Flashtube - Should the name of the article be changed?
- 14 Popular culture section
- 15 Reverted unsourced edit
- 16 What is it called for .....
- 17 History
Animated GIF image
The animated GIF is certainly interesting, but having it as the first image at the beginning of the article is pretty off-putting when trying to read the text!
- Hit escape.--Deglr6328 18:26, 19 September 2005 (UTC)
- Please do not use animated gifs when not requested. It can be dangerous for health, it can trigger seizures for example. This is no-no. And this particular animated gif is extremely annoying. Animate on request, not stop animating on request.
- Perhaps you should lock yourself in a closet for the remainder of your life in order to be certain you will not encounter any possible seizure inducing phenomena EVER. Sorry but the entire world is designed around the needs of the 99.999% of the population that does not experience spontaneous seizures at the slightest provocation. Deal with it.--Deglr6328 08:10, 10 November 2005 (UTC)
- This isn't so much about its seizure-inducing potential as it's about being able to read the text without continually being distracted by a large flashing animation in the peripheral vision. It's a nice image though, so I moved it to the bottom of the article as a compromise. --c3o 12:06, 10 November 2005 (UTC)
Here's a question I wish the article answered:
Why is the light white? or, What is the spectrum of the output?
I would have thought that what you'd get would be a mass of spectral lines, as with a neon sign. So something is definitely different, but what? Current, voltage, gas fill? Is the spectrum a thermal spectrum, a mass of spectral lines that add up to white, or some other spectrum entirely?
- You do get a mass of lines, but the spectrum of xenon just happens to be pretty broad, with strong peaks in (surprise) red, green, and blue. See.
- A flashlamp sould theoretically be made with any of a number of gases, but xenon just happens to have the "white" result :-) .
- Atlant 12:58, 11 Apr 2005 (UTC)
- Atlant is correct, but I will add to the explanation. Quoted from the Perkin-Elmer optoelectronics catalog, "The radiation produced by flashlamps is primarily dependent on current density, and to a lesser extent, on the gas type and pressure". Low current densities produce "spectral line emmision". With xenon, this is usually characterized by a greenish-blue flash, rather than white, (indicating the absence of significant yellow or orange peaks). Xenon has strong peaks in the green, blue, red, UV, and IR portion of the spectrum. Higher current densities produce "continuum emission". Spectral peaks are lower as radiation is produced across the spectrum, with the exception of absorption lines, and is usually centered on the green, which produces the characteristic white light. Current densities that are very high will begin to produce "blackbody radiation", (this is where the arc is so dense it actually begins to absorb some of its own light), and the output color temperature becomes that of a blackbody radiator at 9800 degrees Kelvin, (sort of a sky blue). By carefully balancing voltage and current you can center the output almost anywhere you like. The optimum for output efficency is to pick a voltage/current density that will produce "graybody radiation",(an arc that produces mostly continuum emission, but is still mostly transparant to it's own light), and with xenon, this just happens to be the right combination for white light.
- Xenon's continuum output is centered in the green, so the flash is primarily white. Krypton is centered in the red, and the flash will typically have a pinkish/white color. Flashlamps which I have constructed using argon show an output centered in the near UV, and the flash appears purplish/white. Neon, believe it or not, is centered in the yellow, and the flash is typically a yellowish-orange/white. Air, mostly nitrogen with some oxygen, produces a bluish/white flash similar in color to any electric spark you've ever seen.
Minimum operating voltage
An anonymous editor changed the minimum operating voltage from 100 volts up to 250 volts, and someone else reverted them right back.
I agree with the anonymous editor: I've always found flash lamps operating from something like 250 volts and up (using a voltage doubler from mains voltage in the U.S. and a straight rectifier for 230 vac systems). Even battery systems (as in camera flash units) tend to be 300-voltish.
Has anyone seen any real-world units that operate on 100 volts?
Atlant 12:52, 12 February 2006 (UTC)
- You are probably right. I revert unexplained anon edits TOO easily sometimes.--Deglr6328 22:16, 12 February 2006 (UTC)
Xenon flash lamp in Color Spectropphotometers
Requesting information on the subject matter of Xenon flash lamp for Color spectrophotometer, as employed by GretagMacbeth, DATACOLOR etc.Information requested as under :
1. Technial specifications of Voltage, Wattage, Amperage etc.
2. Source from where to buy.
3. Any information relevent.
- How about searching THE INTERNET.--Deglr6328 16:18, 2 May 2006 (UTC)
The phrase, “a capacitor that is charged to a relatively high voltage” does not make sense. I leave it to someone better versed in electronics to replace it with a phrase that does make sense. -Ahruman 13:49, 5 October 2006 (UTC)
- What about that phrase doesn't make sense to you? Capacitors in xenon flash lamp systems are charged to "relatively high voltages", namely, 300 volts to low thousands of volts.
- Atlant 13:53, 5 October 2006 (UTC)
- Worse, I've realised that there's a Discharge Lamp and a Discharge lamp article. I'll try and sort it out. Bryson430 13:31, 2 August 2007 (UTC)
Operation Section is a bit confusing
I've constructed many flashtubes, and power supplies for them. The section on operation seems to be a bit confusing. The first sentence sounds like it's describing a "Simmer Voltage" type triggering technique, (where the gas is ionized via a constant spark streamer before cuurent is transmitted to the electrodes). The statement "thousands of amperes" is a bit modest; good for small lamps; but more commonly, peak amps can be in the tens-of-thousands to the millions range. The next few sentences seem to be a bit confused themselves, but now apparently describing "external triggering". The last two sentences seem to belong in the "Construction" section. I propose this rewrite as an alternative:
The electrodes of the lamp are usually charged with a relaively high voltage, (generally betwwen 250 to 5000 volts), but the gas exhibits extremely high resistance and the lamp will not conduct electricity until the gas is ionized. Once ionized, or triggered, a spark will form between the electrodes, allowing the capacitor voltage to conduct. The sudden surge of amps quickly heats the gas to a plasma state, where electrical resistance becomes very low. There are several methods of triggering.
"External Triggering" is the most common method of operation, especially for photographic use. The electrodes are charged to a voltage high enough to respond to triggering, but no higher than the lamp's self-flash threshold. An extremely high voltage pulse, the trigger pulse, is applied directly to, or very near, the glass envelope, usually supplied by a step-up transformer. The short, high voltage pulse creates a capacitor effect, generating an equal but opposite voltage inside the tube. This causes ions to stack up on one or both of the electrodes, forming spark streamers, which propagate at a speed of 1 centimeter in 60 nanoseconds. (A trigger pulse must be have a long enough duration to allow one streamer to reach the opposite electrode, or erratic triggering will result.) The triggering can be enhanced by putting a metal band or reflector onto the glass, or by wrapping a thin wire around the lamp from electrode tip to electode tip. When the spark streamers connect, the full amp load from the capacitor conducts through the lamp, heating the xenon to a high enough temperature for the emmision light. When this current pulse travels through the tube, it ionizes the atoms, causing them to jump to higher energy levels. Within the arc plasma three types of particles exist; electrons, positively ionized atoms, and neutral atoms. The ionized atoms number less than 1%, and accounts for all the emitted light. As they recombine with their lost electrons they immediately drop back to a lower energy state, releasing photons in the process.
"Series Triggering" is more common in high powered, water cooled flash lamps, such as those found in lasers. It is almost identical to external triggering, except series triggering applies the high trigger voltage to the cooling water itself, and often the housing of the unit, so care must be taken when handling these type of systems.
"Simmer Voltage Triggering" is the least common method. In this technique, the capacitor voltage is not initially applied to the electodes, but instead, a high voltage spark streamer is maintained between the electrodes. The high current from the capacitor is delivered to the electrodes using a thyristor or a spark-gap. This type of triggering is used mainly in very fast rise time systems, typically those that discharge in the microsecond regime, such as used in high speed stop-motion photography. If this type of system is not used, the spark streamers will still be in contact with the glass when the full amp load passes through the tube, causing wall ablation. Some microsecond flashlamps are triggered by simply "over-volting", which is by applying a voltage to the electrodes which is much higher than the lamp's self-flash threshold, using a spark gap.
I have a photo here that shows why external triggering is a bad idea at very high speeds, but not sure how to upload it here. http://en.wikipedia.org/wiki/Image:Xenon_high_speed_flash_and_external_triggering.jpg#Summary
I think this rewrite gives a better view of different methods of operation. The best book I've ever found on the subject is the Perkin-Elmer catalog, (no, really. It is packed with useful information from the people who invented them, backed up with 12 impecible references of its own), which you can read at http://optoelectronics.perkinelmer.com/content/RelatedLinks/CAT_flash.pdf. Another very good source of information, especially for some simplified math equations, (proper operation will never be achieved without proper math), see Don's Xenon Flash and Strobe webpage at http://members.misty.com/don/xeguide.html#eg . Or read the bible of the industry, "Electronic Flash and Strobe" by Harold Edgerton.Zaereth (talk) 01:10, 17 October 2008 (UTC)
The last line in this section is incorrect. Although the low voltage number of 250 is correct, laser lamps often operate at voltages as high as 5000, but rarely higher than 6000, (beyond this voltage gasses begin to ionize without any trigger, ie: self-flash). Some lamps infact do operate well beyond their self-flash threshold, but those systems are rare. The next problem I see in the last line is the phrase "depending on  the specific gas mixture. Gasses in flashtubes are never mixed for one simple reason. Electricity will pick the path of least resistance. Arc plasma contains less than 1% of ionized particles, which produce 100% of the light. So the electricity will tend to ionize only the atoms that have the lowest electrical resistance. So, if you have a xenon/neon mix, what you really have is a neon flashtube.Zaereth (talk) 00:52, 31 October 2008 (UTC)
Intensity and Duration needs rework
The first paragraph in this section doesn't make much sense. For short pulses the only electrical limit is the total inductance of the system, including that within the capacitor. (For instance, I have a specially made capacitor that will "throw down" in 1.2 microseconds, but after adding the minimal inductance from the leads and flashtube, the fastest flash I could achieve is 3.5us.) Cathode loading is a major consideration, as peak amps rise exponentially as discharge time decreases, but even more of a factor is the amount of energy per square millimeter that the glass can contain. (I've seen these short pulse lamps explode with enough force to stick glass shards into a wall 10 feet away, at only 80 joules, and a sound like a shotgun going off!) Quartz glass, 1mm thick, can usually contain about 200 watts per square centimeter maximum with liquid cooling, but only about 30 watts per cm squared with air cooling, (measuring the inside circumference, times the length between electrodes). Other glasses, much less.
For long pulses, or continuous operation, heating of the glass and electrodes is much more of a wear factor. Too much power loading at the cathode results in "sputter", while too much at the anode, usually combined with wall ablation of the glass, results in oxidization.Zaereth (talk) 18:56, 5 November 2008 (UTC)
- I agree with this statement, that it is not only the inductance is the limits the flash duration, it would be the time constant of the LC circuit (including the capacitance of the capacitor). In lower voltage flashes (such as small cameras flashes) the resistance of the plasma in the tube will also have an impact on the duration of the flash (RC time constant, which I think is the reason to your 3.5 us duration). Unless someone have reliable references for the current statement written in the article and in which context it is valid, i suggest to remove that claim. In addition to the electrical limit you also have an afterglow and a delay in the light emission from the gas (the current ionizes the gas, but the light is produced when electrons recombine with the gas, or when they fall down from metastable states, which can take more than several milliseconds for some gases) EV1TE (talk) 13:01, 21 March 2014 (UTC)
- Resistance plays a big role in efficiency, but a very small role in duration. The circuits are normally very low in resistance to begin with. As pulse duration decreases, capacitance must also be decreased and voltage be increased proportionately, or else the current density gets too high. For microsecond pulses, you're usually looking at voltages in the range 5000 to 100,000 volts or higher (quite often surpassing the self-flash rating of the lamp) and capacitances in the micro or picofarads. Higher voltages not only better overcome the resistance of the metal components of the circuit, but they increase the negative resistance of the gas. making it more conductive than lower voltages would. Therefore, as pulse duration decreases, resistance becomes less of a factor, not more.
- Ionization, recombination, and reionization is something that happens to individual atoms, not the gas as a whole. At any given time during the pulse, only about 1% of the plasma is ionized. As the ions bump into neutral atoms, they transfer electrons, and the movement of electricity through the gas very much resembles a relay race, where ions and atoms are constantly moving back and forth in very short distances, transferring electrons as they go. Faint light emission begins as soon as the gas ionizes, and gets brighter during the pulse as the plasma gets hotter. Prepulse techniques are often used to overcome the limitations of rise-time.
- Afterglows (glows that exist after the electrical pulse shuts down) are very short lived, (typically in the range of microseconds, not milliseconds) and much dimmer than the actual pulse, and so are inconsequential for photographic and laser applications. These afterglows exist from ionized atoms and free-electrons remaining after the pulse shuts down. and are used in prepulse techniques, but the main pulse must come immediately after the prepulse, before the ions have a chance to recombine, or else it won't work. This afterglow is mainly a limit to repetition rate, but does not have much effect on the pulse duration.
- For very short pulses, the inductance of the flashtube itself becomes the largest limiting factor. The flashtube will have the same inductance as a round wire of the same length. The shape of the coils and connections in the capacitor and of the leads can be adjusted to reduce inductance to a minimum. Typically, you would want to reduce inductance by using leads and connections with a very large surface area and the thinnest cross-section possible. Special axial leads are available for this purpose, or thin, wide strips of metal can be used. However, there is very little that can be done to reduce inductance in the lamp. For extremely short pulses, Edgerton recommended a lamp with a large bore and the shortest length possible. For dye lasers, special axial lamps are often used o reduce inductance.
Changes have been implemented
Vraiable Pulse Width Control triggering
It might be helpful to add a full paragraph in the article on the circuit you're describing there. The circuit is often called a "Variable Pulse Width Control" circuit, as is described in the Perkin Elmer catalog which I referenced. There are many ways to put one together, and can even be designed to produce square-wave pulses. Perhaps if we start out with the name, then a small paragraph to describe the circuit that would fit better with the style of the rest of the article. What do you think?Zaereth (talk) 23:22, 4 December 2008 (UTC)
- I think that sounds like a great idea. Would it be legally permissible under Fair Use to illustrate the concept with one of the schematics from the document that I used as a reference in the article, or a schematic based on one of those (possibly simplified, for clarity?)? Ilikefood (talk) 23:54, 4 December 2008 (UTC)
- I'm rather new to Wikipedia, so I don't know the answer to that question. Personally, I think a paragraph that gives a basic overall view is sufficient, as an encyclopedia should not be an instruction manual. Those who are interested, I think, should have no problem checking out the reference. Zaereth (talk) 00:07, 5 December 2008 (UTC)
I'd like to add just a little more info to this subsection. This system is used frequently in high average power laser systems, and can produce pulses ranging from .5 milliseconds to over 20 milliseconds. It can be used with any of the triggering techniques, like external and series, and can produce square wave pulses. It can even be used with simmer voltage to produce a "modulated" continuous wave output, with repetition rates over 300 hertz. With the proper large bore, water cooled flashlamp, several kilowatts of average power output can be obtained. Zaereth (talk) 18:31, 31 December 2008 (UTC)
Other gasses and safety
Having completed some further research, I'm adding a couple of new sections, one on other gasses, and the other on safety. If there is any question or comment, please make it here.Zaereth (talk) 19:01, 17 December 2008 (UTC)
Requested moves: Xenon Flash Lamp to Flashtube - Should the name of the article be changed?
Popular culture section
A statement was recently added to the Application section about the use of xenon flashtubes in the movie The Andromeda Strain. Since this is not an actual application, I have moved it to a new section labeled popular culture. Zaereth (talk) 18:09, 9 April 2009 (UTC)
Reverted unsourced edit
I reverted the following edit as unsourced and incorrect. First designed by engineers Hunter H. Hetfeld and Luke J. Valenter in the late 80's, I'll try to gather some sources on the origins, but flashtube technology got its start in the late 1800s, as open air sparks by photographers like Ernst Mach. I believe Tesla created the first "contained arc" flash apparatus, but it was Harold Edgerton who was the main pioneer in the field, and that was back in the 1930s. Flashtubes have been used in lasers since the 1960s. Zaereth (talk) 23:46, 18 January 2010 (UTC)
What is it called for .....
- I'm not sure what you're asking for. Can you clarify? The light in the above photo is from an incandescent bulb. There is nothing gradual about a flashtube. The light is full spectrum, (all colors), and the flash quickly builds to full power, and then shuts down instantly, as seen in the animation st the bottom of the article. Zaereth (talk) 17:28, 26 January 2010 (UTC)
- The first flash apparatus Edgerton made used a mercury arc rectifyer. The flashtube (ie: noble gas discharge lamp) came afterward. It might be worth mentioning that Edgerton employed General Electric to do the glassblowing, but the flashtube as we know it today is something that evolved over the entire decade of the 1930s. Zaereth (talk) 03:00, 1 November 2010 (UTC)