# Difference between Xenon, Krypt... etc...bulbs



## ViReN (Aug 7, 2004)

Hi All,

I have a very specific question, it always quizzels me...

What is the difference between the the following incand lamp types
1) Xenon
2) Krypton
3) Halogen
4) Normal Lamps...
5) Any More Technologies in incand

What are the brightness levels, Lifetimes, Advantages, Disadvantages, any minimum voltages / currents, Typical applications, CRI, Comparisons & Comparitive Data....

So many doubts.... Is there any web page / link where i can get good information... i did google first before posting here.. but i got really vague results...

Help .... /ubbthreads/images/graemlins/help.gif

Thanks & Regards,
ViReN


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## mattheww50 (Aug 7, 2004)

Xenon and Krypton are both inert gasses. That allows somewhat higher filament temperatures, and longer life since even at the temperatures of the filament, no chemical reactions take place between the filament and the gas inside the bult envelope. However there is loss of brightness with age, because some of the filament material boils off the filament and deposits itself on the glass, hence the darkend areas on many frosted lamps at end of life, and the darkened ends of fluorsecent tubes.

Halogens are very reactive elements, the main advantage is they also allow higher filament temperatures, but prevent the deposition of material on the glass envelope. Material does boil off, and does deposit on the glass envelope, however it reacts with the halogen (usually Iodine, sometimes bromine), and ends up being removed from the walls and redeposited on the filament. This takes place at fairly high temperatures, so the application has to be designed so the that filament can reach the required temperatures for the reaction to take place. The design also has to limit the envelope temperature to prevent envelope or seal failure. These lamps have to run long enough for the halogen cycle to operate. The halogens generally have the highest Color temperatures and highest efficiencies. CRI for all incandescents is a non issue. CRI is a measurement of how well the spectral output of a lamp approximates a 'black body' at the stated colour temperature. Filaments are for all practical purposes black bodies, so they have CRI's of 100. Lifetime is mostly is mostly related to filament temperature, which is driven by applied voltage. The higher the filament temp, the higher the colour temperature, the higher the luminous efficiency and the shorter the life. Radiated energy goes up at T^4, so even modest increases in color temperature (filament temp) improve the Lumious efficiency. The higher temperatures also speed up the filament evaporation and deposition on the envelope, so brighness is lost unless you can remove the deposits (which is what a halogen lamp does).


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## js (Aug 8, 2004)

ViReN,

Just wanted to clarify/add to mattheww50's excellent (as usual) post:

Xenon and Krypton are both Halogen's: so when you say "halogen" you mean either one or the other. Halogen is a general term indicating elements in a column of the periodic table, IIRC.

Xenon lamps are, from what I've seen, better than Krypton lamps.

Normal lamps are always worse than halogens, from what I've seen, but I think they run cooler.

And who's to say what new technologies may or may not come along. Everyone assumes that incans will go the way of the dinosaur, and they probably will, but it's not a done deal. It's not certain. Perhaps there will be another break through like the advent of the halogen lamp, and incans will get a new lease on life. We shall see.

Oh, and matthew, I checked the melting temp of Tungsten and it's *6000+ degrees F*! Holy Cow! Perhaps the CCT is the filament temp after all. I don't know. I would think that that kind of temp at the filament, would mean heat conduction down to the normal metal lamp leads and would melt them. Plus the CCT means "correlated color temperature". Wouldn't they just call it filament temperature if the FT=CCT? Eh. Not sure. But I find it hard to believe that the filament really is 3400 F in a "hot" xenon lamp. I'll look into it some more, unless you have a definitive answer.


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## Echo63 (Aug 8, 2004)

hang on a tic - both xenon and krypton are halogens ? 
so what is in a globe that is marketed as a halogen ?
like the headlight globes

and what about the quartz iodine/iodide globes (like car headlights)


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## js (Aug 8, 2004)

The gas fill of a lamp marketed as "halogen" can be either xenon or krypton.

Not sure about the iodine globes. Wild guess: probably iodine at a lower than 1 atmosphere pressure. Iodine is a liquid at standard temperature and pressure. Lower the pressure or raise the temperature and it turns into a gas.

The halogens are in the VIIIA column of the periodic table of the elements and include, in acsending order of atomic weight: Helium, Neon, Argon, Krypton, Xenon, and Radon.


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## bwaites (Aug 8, 2004)

Echo, none of the bulbs, including the car bulbs, so far as I know actually have only ONE gas in them. The proprietary mix is what distinguishes the bulbs from each other and from manufacturer to manufacturer.

Some have more Xenon, some more Krypton, some more Iodine, some more bromine, etc.

Bill


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## jayflash (Aug 8, 2004)

Does anyone know how long to keep a flashlight on to insure that a complete halogen cycle will take place? Does the glass globe, itself, need to reach a high enough temperature or just the filament and gas?


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## ViReN (Aug 8, 2004)

Great Responses... THanks Dudes /ubbthreads/images/graemlins/smile.gif

I was really unclear about the things....

In early days... there were just 2 types of bulbs (that i know) ... the normal bulbs (the dull ones) & the Halogen's ... the brighter ones... mostly used for lighting special applications like spot lights & Vehicle Head Lamps...

Off late.... Krypton & Xenon were in the market.... 

Xenon (Headlamps.. for car)... i think is wrongly being marketed... they use a Blue Glass filter to product whiter light....where as normal halogen's dont use any kind of filters ... some of the fog lights are coated with a very thin layer of gold to produce a yellow light i guess...

-ViReN


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## easilyled (Aug 8, 2004)

I am positive that Halogens are in Group 7 of the periodic
table and are Fluorine, Chlorine, Bromine, Iodine etc.

Xenon and Krypton are DEFINITELY not halogens, but 
inert gases as mattheww50 said.


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## Size15's (Aug 8, 2004)

My understanding is that a Halogen filled lamp allows the "Halogen Cycle" to prolong the lifespan of the Tungsten filament. Xenon is a gas used at high pressure to make it more difficult for the Tungsten to evaporate from the filament in the first place. Therefore a high pressure Xenon/Halogen bulb can be driven harder - for brighter, whiter light.

Al


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## Ginseng (Aug 8, 2004)

Right,
Group 8 are the noble elements. Group 7 are halogens.
Wilkey


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## cannon50 (Aug 8, 2004)

I believe that the halogen lamps contain halide salts while xenon and krypton are the nobel gases that are added to the Xe and Kr bulbs to allow higher internal pressures than argon type would allow.


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## jtr1962 (Aug 8, 2004)

[ QUOTE ]
*js said:*
And who's to say what new technologies may or may not come along. Everyone assumes that incans will go the way of the dinosaur, and they probably will, but it's not a done deal. It's not certain. Perhaps there will be another break through like the advent of the halogen lamp, and incans will get a new lease on life. We shall see.


[/ QUOTE ]
About the only thing I see giving incandescents a new lease on life is a new filament material that can be run at maybe 5000K to 6000K. Combine that with coatings to reflect the IR and UV from the filament back into the bulb so as to lower heating requirements, and you may very well see an incandescent with well over 100 lm/W efficiency that also gives a nice white light instead of the "off-white" typical of incandescents. Short of that, however, I see the incandescent light dying out eventually as LEDs with much higher efficiency, longer life, better color temp, and CRIs approaching 100 are made.

[ QUOTE ]

I checked the melting temp of Tungsten and it's *6000+ degrees F*! Holy Cow! Perhaps the CCT is the filament temp after all. I don't know. I would think that that kind of temp at the filament, would mean heat conduction down to the normal metal lamp leads and would melt them. Plus the CCT means "correlated color temperature". Wouldn't they just call it filament temperature if the FT=CCT? Eh. Not sure. But I find it hard to believe that the filament really is 3400 F in a "hot" xenon lamp.

[/ QUOTE ]
Actually, the filament does run at the CCT, and I think with most incandescents they just call it color temp rather than CCT. CCT is only necessary when the emitted radiation falls off the Planckian locus. Since a filament is for all intents and purposes a blackbody this isn't necessary. CCT only comes into play for incandescents when you use filters to get higher color temps. Solux has a line of MR-16 halogen lamps in color temps of 3500K, 4100K, and 4700K. Obviously the filament doesn't operate anywhere near those temperatures. CRI is said to be 99+.

BTW, I think you meant 3400K, not 3400°F, as the temperature of a hot xenon lamp (3400K = 5660°F). This isn't far from the melting point of tungsten, and represents the limit that an incandescent light can operate at (maybe you can go to 3500K, but the filament will die within seconds or minutes at most).


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## brightnorm (Aug 9, 2004)

[ QUOTE ]
*cannon50 said:*
I believe that the halogen lamps contain halide salts while xenon and krypton are the nobel gases that are added to the Xe and Kr bulbs to allow higher internal pressures than argon type would allow. 

[/ QUOTE ]

I thought I had this all figured out but now I'm confused again. My understanding is:

-Halogen is not an element but a class of elements 
-Xenon and krypton are the two most popular inert gses that fill high intensity bulbs,(either individually or in combination)?
-Some members of the halogen family (iodine, bromine etc?)are added to "sweeten" the xenon/krypton performance 
-The "halogen cycle" is the redepositing of burned-off tungsten back to the filiment, made possible by the high internal pressure and the nature of the inert gases. This occurs only when filiment temperature is high enough which is why keeping voltage up is so important.

Will someone please correct this and state the facts in clear, complete and concise terms so I can finally understand this?

Brightnorm


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## iddibhai (Aug 9, 2004)

they already have HIR (Halogen Infra Red), bulb is spherical over the filament section, coated in IR reflecting materials, allowing better output; take the example of 9006 headlamps; nominally 1000 lumens, HIR outputs 1900 lumens.


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## js (Aug 9, 2004)

[ QUOTE ]
*easilyled said:*
I am positive that Halogens are in Group 7 of the periodic
table and are Fluorine, Chlorine, Bromine, Iodine etc.

Xenon and Krypton are DEFINITELY not halogens, but 
inert gases as mattheww50 said. 

[/ QUOTE ]

Oops. Yes. That column is NOT the halides. Sorry.

As Bill said, the fill of a halogen lamp contains a mix of gases, including one or more of the non-reactive noble gases.


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## js (Aug 9, 2004)

[ QUOTE ]
*jtr1962 said:*
[ QUOTE ]
*js said:*
And who's to say what new technologies may or may not come along. Everyone assumes that incans will go the way of the dinosaur, and they probably will, but it's not a done deal. It's not certain. Perhaps there will be another break through like the advent of the halogen lamp, and incans will get a new lease on life. We shall see.


[/ QUOTE ]
About the only thing I see giving incandescents a new lease on life is a new filament material that can be run at maybe 5000K to 6000K. Combine that with coatings to reflect the IR and UV from the filament back into the bulb so as to lower heating requirements, and you may very well see an incandescent with well over 100 lm/W efficiency that also gives a nice white light instead of the "off-white" typical of incandescents. Short of that, however, I see the incandescent light dying out eventually as LEDs with much higher efficiency, longer life, better color temp, and CRIs approaching 100 are made.

[ QUOTE ]

I checked the melting temp of Tungsten and it's *6000+ degrees F*! Holy Cow! Perhaps the CCT is the filament temp after all. I don't know. I would think that that kind of temp at the filament, would mean heat conduction down to the normal metal lamp leads and would melt them. Plus the CCT means "correlated color temperature". Wouldn't they just call it filament temperature if the FT=CCT? Eh. Not sure. But I find it hard to believe that the filament really is 3400 F in a "hot" xenon lamp.

[/ QUOTE ]
Actually, the filament does run at the CCT, and I think with most incandescents they just call it color temp rather than CCT. CCT is only necessary when the emitted radiation falls off the Planckian locus. Since a filament is for all intents and purposes a blackbody this isn't necessary. CCT only comes into play for incandescents when you use filters to get higher color temps. Solux has a line of MR-16 halogen lamps in color temps of 3500K, 4100K, and 4700K. Obviously the filament doesn't operate anywhere near those temperatures. CRI is said to be 99+.

BTW, I think you meant 3400K, not 3400°F, as the temperature of a hot xenon lamp (3400K = 5660°F). This isn't far from the melting point of tungsten, and represents the limit that an incandescent light can operate at (maybe you can go to 3500K, but the filament will die within seconds or minutes at most). 

[/ QUOTE ]

AH! Thanks for this! That makes sense.


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## js (Aug 9, 2004)

jr1962,

So if the filament is running that hot, why doesn't it melt the electrical/mechanical wires which hold it in position?


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## NewBie (Aug 9, 2004)

[ QUOTE ]
*js said:*

And who's to say what new technologies may or may not come along. Everyone assumes that incans will go the way of the dinosaur, and they probably will, but it's not a done deal. It's not certain. Perhaps there will be another break through like the advent of the halogen lamp, and incans will get a new lease on life. We shall see.


[/ QUOTE ]

I guess you haven't seen photonic lattices yet?

http://www.sandia.gov/media/NewsRel/NR2002/tungsten.htm

"This could raise the efficiency of an incandescent electric bulb from 5 percent to greater than 60 percent."

This would raise the efficiency by 1,200%


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## js (Aug 9, 2004)

NewBie, I'll check that out.

I have a bad tendency to think I know what I'm talking about when I really don't know what the (*&T^! I'm talking about.

In an attempt to remedy this I have started researching tungsten halogen lamps. I thought this link would be worth while to post for the benefit of our discussion and to help answer some of the questions that were originally asked. I'll be back later when I have a clue or maybe more than just one clue. Sorry everyone.


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## ViReN (Aug 9, 2004)

Whola... Again a Great deal of Information /ubbthreads/images/graemlins/smile.gif

Kool Links... Great Knowledge... New Technologies... Future Looks great for Filament & 3D Bulbs....

This Dinasour (energy consuming) is not going away soon, rather, it will eat less (of power) and give out more (of light energy) becoming more and more efficient....and at the same time, will loose weight (will run a bit cooler /ubbthreads/images/graemlins/wink.gif)

-ViReN


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## js (Aug 9, 2004)

NewBie,

All I can say is WOW! That would make incandescent technology the hands-down winner in illumination! Incredible! I love it. Hehe, sorry all you LED-lovers, you're days are numbered. I'll get to make posts like "how long before no LED production light is offered?" What a great day that will be!

Just kidding! I have nothing against LED's and actually think they're pretty cool, but if we could increase incan efficiency to 60 percent, that would blow LED's away. That would blow ALL current light sources away.

And as for the original question of this thread, I can safely say that xenon is a better fill gas than krypton, which in turn is a better fill gas than argon. All three are used, but xenon is very costly, and so is krypton, but not by as much, so those two are only used in high performance, small sized lamps. xenon works better to bump the tungsten atoms back to the filament, and conducts less heat away to the glass capsule, due to its larger atoms than either krypton or argon.

And I found out that the tungsten/non-tungsten interface is a tungsten/molybdenem (sp?) interface with a very sharp temperature drop across the transition.

And I found out that iodine is the most common halogen used to make the halogen cycle work. Bromine is/was also used. If they can figure out how to make florine work, it would be the best at tungsten reeposition on the filament, as it would redeposit evenly, whereas iodine redeposits more on the cold areas than the hotter areas, which means that hot spots get thinner and hotter and poof! You have a broken filament. The problem with florine at present is that it attacks the non-tungsten part of the conduction path and corrodes it.

Also the glass used for tungsten halogen lamps is quartz glass, hence the term "quartz halogen lamp".


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## KevinL (Aug 10, 2004)

Aurora/Phoenix/Mule with photonic lattice......huhuhuhuhuhuhuhuhuhuhuh.... I think I'm losing it.. /ubbthreads/images/graemlins/faint.gif

There are new frontiers to conquer, after all /ubbthreads/images/graemlins/smile.gif


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## js (Aug 10, 2004)

This link on tungsten halogen lamps is pretty good and refers to a book, which I'd like to look at.


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## h_nu (Aug 10, 2004)

Hope this isn't hijacking the thread. I won't be offended if a moderator moves it.

Tungsten does have a high melting point but early bulbs used Carbon. Carbon has a low vapor pressure but also had more resistance to breaking due to vibration and a higher resistance at room temperature which resulted in less of a surge current when turned on. My grandfather gave me a few old light bulbs that he had kept on for decades. They were fairly dim and one even had a nipple at the top where the vacuum bulb was drawn.

My grandfather asked me a question that started me as a flashaholic. What if someone had thought to fill the early vacuum bulbs with relatively cheap Argon instead of using a vacuum? How would the history of light bulb development have changed?

Hmmm?


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## Double_A (Aug 10, 2004)

easilyled-

Thank you, I thought I was going nuts. I pulled out a periodic table and had to check myself. You and matthewww50 are correct. And if I'm not mistaken Xenon, Krypton, Argon are refered to as "Noble Gases" since they are so unreactive.

GregR


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## jtr1962 (Aug 11, 2004)

[ QUOTE ]
*h_nu said:*
Tungsten does have a high melting point but early bulbs used Carbon. Carbon has a low vapor pressure but also had more resistance to breaking due to vibration and a higher resistance at room temperature which resulted in less of a surge current when turned on. My grandfather gave me a few old light bulbs that he had kept on for decades. They were fairly dim and one even had a nipple at the top where the vacuum bulb was drawn.

My grandfather asked me a question that started me as a flashaholic. What if someone had thought to fill the early vacuum bulbs with relatively cheap Argon instead of using a vacuum? How would the history of light bulb development have changed?


[/ QUOTE ]
Maybe incandescents would have been a little whiter and more efficient. Tungsten melts at 3683K while carbon melts at 3823K. However, the highest filament temperatures possible with tugsten lamps are ~3400K, and even then life is only a few tens of hours. I wonder with appropriate fill gases if it is possible to operate carbon closer to its melting point and still get reasonable life. An incandescent light operating at, say, 3700K, would have an efficiency of at least 40 to 50 lm/W, and a much more pleasing color temperature than the usual 2800K to 3000K. I just wonder if it would be possible to get 1000 hours of life out of a carbon filament operating at those temperatures. Perhaps experiments with fullerenes (a form of carbon) will lead to materials with melting points of 4000K, 5000K, even 6000K. These would make ideal incandescent filaments. I heard diamond melts at 4363K but its price and non-conductive nature would make it a poor candidate for a light bulb filament.

As an aside, the tungsten lattice mentioned here doesn't really classify as an incandescent light. It is more a quantum device like an LED which uses low-level heat rather than electrons as a means of excitation. Even it it works and is commercially viable it would not be form of incandescent lighting. As I said, if one defines incandescent light to mean heating a material to make light, I think short of new filament materials that operate much hotter than today's tungsten filaments, the incandescent will mostly disappear. I'd say we'll still always have incandescent lamps made but in the same way tube amplifiers are made today-mainly to serve very small niche markets.


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## js (Aug 11, 2004)

Regarding carbon filaments:

[ QUOTE ]
Melting point of Tungsten = 3383 degrees Centigrade + 273.16 = 3656.16 degrees Kelvin (which is less than carbon at 3500 degrees Centigrade + 273.16 = 3773.16 degrees Kelvin.) but its low rate of vaporization (compared to carbon) makes up for the lower melting point since carbon can only be heated to about 2500 degrees Centigrade (see page 4 of Tungsten Halogen Low Voltage Lamps Photo Optics). 


[/ QUOTE ]


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## jtr1962 (Aug 11, 2004)

Here is as close a link as I could get for that Tungsten Halogen Photo Optics book. Click on the title _Engineering Bulletin - Technology and Application - Tungsten Halogen Low Voltage Lamps Photo Optics_ and the pdf should open in a new window. Adobe 5 let me save a copy to my hard drive.


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## js (Aug 11, 2004)

jtr1962,

/ubbthreads/images/graemlins/thumbsup.gif /ubbthreads/images/graemlins/thumbsup.gif /ubbthreads/images/graemlins/thumbsup.gif /ubbthreads/images/graemlins/bowdown.gif /ubbthreads/images/graemlins/bowdown.gif /ubbthreads/images/graemlins/bowdown.gif

NICE WORK! I did a quick book search for this and came up with nada. I was definitely going to order it. But now, thanks to you, I have it for free. Excellent. Most excellent. Thank you very very much.


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## jtr1962 (Aug 11, 2004)

You're quite welcome! /ubbthreads/images/graemlins/grinser2.gif

I _did_ have a hell of a time finding it. It's buried in some obscure corner of Slyvania's site. Should make interesting reading.


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## js (Aug 11, 2004)

I started reading this 44 page bulliten, and *it is fantastic!* Everyone who wants to know about tungsten halogen incandescent lamps (which are used almost exclusively in the flashlights we all like on CPF) should consider this a MUST READ.

Also, I should mention that this document gives me increased respect for Welch Allyn. Osram Sylvania has this to say about lamps which have no front exhaust tube tip off (i.e. lamps with a smooth round front and not a glass point):

[ QUOTE ]
SO far there are very few lamps on the market without a visible exhaust tube tip-off. These are evacuated, cleaned, and filled through the pinch, a technically very demanding manufacturing process in which the quality of large-scale production quantities must be closely monitored.

[/ QUOTE ]


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## ViReN (Aug 11, 2004)

Wow.... This turned out to be a very very informative page now /ubbthreads/images/graemlins/smile.gif

Thanks to Each & Every Knowledgable person.. who has answered to my simple queries.. and making this page as a Unique Must-Read kinda post ... may be.. Moderators could *stick* it for reference... well... its up to em...its just a suggestion

-ViReN


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## js (Aug 11, 2004)

[ QUOTE ]
*ViReN said:*
Wow.... This turned out to be a very very informative page now /ubbthreads/images/graemlins/smile.gif

Thanks to Each & Every Knowledgable person.. who has answered to my simple queries.. and making this page as a Unique Must-Read kinda post ... may be.. Moderators could *stick* it for reference... well... its up to em...its just a suggestion

-ViReN 

[/ QUOTE ]

To that end, it might be a good idea to change the title of the thread to something like "Primer on tungsten halogen incandescent technology, with links, and plenty of mistakes by js (who now thinks he is somewhat better informed)."

Or perhaps shorter than that. /ubbthreads/images/graemlins/grin.gif


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## mattheww50 (Aug 11, 2004)

Several comments on previous posts. While the melting point of Tungsten may be close to 6000F, colour temperature is measured in degrees Kelvin, which is a centigrade like system, but works from Absolute zero. 6000F is about about 3600K. You don't actually want to get anywhere near 3600K in the lamp. Contrary to another assertion, the pressure of the gas inside the lamp envelope has no effect at ALL on the vaporization of the filament. If I take a tank and pressurize it to 500psi, and partially fill it with water. I will raise the temperature at which visible boiling takes place, but that will not prevent the partial pressure of water vapor inside the tank from rising to 1 atmosphere when the water hits 212F. That fact that isn't visibly boiling doesn't mean that water isn't being converted to water vapor at a high rate. Boiling occurs when the partial pressure equal local pressure. The fact that the atmosphere pressure is 15psi doesn't prevent the sublimation of Ice to water vapor even when the vapor pressure of water is only 5% of atmospheric pressue (this is how ice/snow disappears even though the temperature may be below freezing!) It won't happen if the relative humdity is 100%, but any relative humdity below 100%, it will occur.

What counts is the partial pressure of the material being boiled off. The partial pressure of tungsten in a lamp is tiny even at 3000K, but even at tiny partial pressures, over thousand of hours, you can in fact sublime enough of the filament to darken the envelope. 

The partial pressure roughly doubles for each 10C the temperature goes up. The obvious implication is that higher filament temperatures reduce lamp life very dramatically. The reality is that even in a lamp with a 10 hour life, the rate at which the filament boils off is very low initially.


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## David_Campen (Aug 11, 2004)

[ QUOTE ]
Contrary to another assertion, the pressure of the gas inside the lamp envelope has no effect at ALL on the vaporization of the filament.

[/ QUOTE ]
So why bother to put the gas in if it has no effect?


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## Size15's (Aug 11, 2004)

But the higher pressure stops the vapourised filament from reaching the glass though right?


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## mattheww50 (Aug 11, 2004)

Only in the sense that it reduces the mean free path, but the mean free path of the boiled off material is already orders of magnitude less than the distance from filament to envelope even at 1 atmosphere. It takes very high vaccuum to even produce a 1cm mean free path for an electron. The only real effect is likely to be a more random distribution, i.e. the darkening of the envelope will be spread over a larger area (which is probably of some benefit). Normally the inverse square law would apply, so you would expect the most darkening to be nearest the filament, however if you make the mean free path short enough, you end up with a more or less random distribution, and that may result in the appearance of less darkening of the envelope. All that has really happened is the tungsten is better scattered! The secondary effect is that Krypton and Xenon are both fairly heavy, so the collisions also reduce the energy of the Tunsten atoms, which probably reduces the ability to hit and stick to the envelope.

The main reason to have the gas inside is that it prevents any sort of chemical reaction from occuring with the filament. At filament temperatures, most gases dissociate and can be very reactive, so even something like Carbon Dioxide is actuallly quite reactive for the same reason you cannot use carbon dioxide on a magnesium fire. The temperature breaks the Carbon Oxygen bond, and Oxygen then units with the Magnesium, making the fire much worse!


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## David_Campen (Aug 12, 2004)

[ QUOTE ]
Only in the sense that it reduces the mean free path, but the mean free path of the boiled off material is already orders of magnitude less than the distance from filament to envelope even at 1 atmosphere. It takes very high vaccuum to even produce a 1cm mean free path for an electron. The only real effect is likely to be a more random distribution, i.e. the darkening of the envelope will be spread over a larger area (which is probably of some benefit). Normally the inverse square law would apply, so you would expect the most darkening to be nearest the filament, however if you make the mean free path short enough, you end up with a more or less random distribution, and that may result in the appearance of less darkening of the envelope. All that has really happened is the tungsten is better scattered! The secondary effect is that Krypton and Xenon are both fairly heavy, so the collisions also reduce the energy of the Tunsten atoms, which probably reduces the ability to hit and stick to the envelope.

The main reason to have the gas inside is that it prevents any sort of chemical reaction from occuring with the filament. At filament temperatures, most gases dissociate and can be very reactive, so even something like Carbon Dioxide is actuallly quite reactive for the same reason you cannot use carbon dioxide on a magnesium fire. The temperature breaks the Carbon Oxygen bond, and Oxygen then units with the Magnesium, making the fire much worse! 

[/ QUOTE ]
Gee, first you say that having the gas in there doesn't matter then you say it does - maybe for one reason or perhaps another reason or is it a third reason! Might there be a bit of guessing going on here?


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## Ginseng (Aug 12, 2004)

Matt,

I have a Master's degree in Chemical Engineering and I'm having trouble following you. Might you be able to put that in layman's terms...a la Bill Nye the Science Guy? BTW, at these temperatures and pressures, the mean free path is not likely to have much significance. As for the reactivity of CO2, aren't you're talking about a rather extreme situation because of the oxidizing power of elemental magnesium? You can also achieve this "reactivity" by pushing CO2 into a supercritical fluid state but I don't think that applies here.

Wilkey


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## mattheww50 (Aug 15, 2004)

1). The gas has no effect on preventing the filament from boiling off. If may have some effect in preventing deposition of the filament material on the glass. That effect however is related to the gas making it more difficult for the metal vapor to reach the glass envelope with sufficient energy to stic.Krypton and Xenon are aslo reasonably good thermal conductors, so the very short mean free path means most of the thermal energy the metal molecules have acquired will be lost in collisions with the gas molecules and imparted to the xenon and krypton molecules.
2). Reactivity of Magnesium isnt the problem. The bind is that when the temperature gets high enough, the thermal energy can exceed the bond energy, so the molecular bonds can break, and the molecules start to dissociate. The question them becomes is the bond energy of a metal carbide or metal oxide higher then then thermal energy. If it is, then the gas molecules dissassociate, and the more reactive atoms may form stable compounds with whatever else is present if the thermal energey is appreciably lower than the bond bond energy in those compounds. 

The Carbon-Oxygen bond energy isn't especially high.

That requires substantial temperatures, but that's the kind of temps you get with a tungsten filament.


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## Ginseng (Aug 15, 2004)

In the words of Homer Simpson..."Can you dumb it down a bit? Dumber. Dumber. Not getting you. More."


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## NewBie (Aug 15, 2004)

[ QUOTE ]
*mattheww50 said:*
1). The gas has no effect on preventing the filament from boiling off. If may have some effect in preventing deposition of the filament material on the glass. That effect however is related to the gas making it more difficult for the metal vapor to reach the glass envelope with sufficient energy to stic.Krypton and Xenon are aslo reasonably good thermal conductors, so the very short mean free path means most of the thermal energy the metal molecules have acquired will be lost in collisions with the gas molecules and imparted to the xenon and krypton molecules.
2). Reactivity of Magnesium isnt the problem. The bind is that when the temperature gets high enough, the thermal energy can exceed the bond energy, so the molecular bonds can break, and the molecules start to dissociate. The question them becomes is the bond energy of a metal carbide or metal oxide higher then then thermal energy. If it is, then the gas molecules dissassociate, and the more reactive atoms may form stable compounds with whatever else is present if the thermal energey is appreciably lower than the bond bond energy in those compounds. 

The Carbon-Oxygen bond energy isn't especially high.

That requires substantial temperatures, but that's the kind of temps you get with a tungsten filament. 

[/ QUOTE ]

Okay, so, with what sort of actual do you write this? Do you have any links that explain this process in much more detail?

Here is Don Klipstein's comments on it:

Sometimes, premium fill gases such as krypton or xenon are used. These gases have larger atoms that are better at bouncing evaporated tungsten atoms back to the filament. These gases also conduct heat less than argon. Of these two gases, xenon is better, but more expensive. Either of these gases will significantly improve the life of the bulb, or result in some improvement in efficiency, or both. Often, the cost of these gases makes it uneconomical to use them.

(my insert comment, later on he says this in more detail)

A halogen bulb is an ordinary incandescent bulb, with a few modifications. The fill gas includes traces of a halogen, often but not necessarily iodine. The purpose of this halogen is to return evaporated tungsten to the filament.
As tungsten evaporates from the filament, it usually condenses on the inner surface of the bulb. The halogen is chemically reactive, and combines with this tungsten deposit on the glass to produce tungsten halides, which evaporate fairly easily. When the tungsten halide reaches the filament, the intense heat of the filament causes the halide to break down, releasing tungsten back to the filament.
This process, known as the halogen cycle, extends the life of the filament somewhat. Problems with uneven filament evaporation and uneven deposition of tungsten onto the filament by the halogen cycle do occur, which limits the ability of the halogen cycle to prolong the life of the bulb. However, the halogen cycle keeps the inner surface of the bulb clean. This lets halogen bulbs stay close to full brightness as they age.
In order for the halogen cycle to work, the bulb surface must be very hot, generally over 250 degrees Celsius (482 degrees Fahrenheit). The halogen may not adequately vaporize or fail to adequately react with condensed tungsten if the bulb is too cool. This means that the bulb must be small and made of either quartz or a high-strength, heat-resistant grade of glass known as "hard glass".
Since the bulb is small and usually fairly strong, the bulb can be filled with gas to a higher pressure than usual. This slows down the evaporation of the filament. In addition, the small size of the bulb sometimes makes it economical to use premium fill gases such as krypton or xenon instead of the cheaper argon. The higher pressure and better fill gases can extend the life of the bulb and/or permit a higher filament temperature that results in higher efficiency. Any use of premium fill gases also results in less heat being conducted from the filament by the fill gas, meaning more energy leaves the filament by radiation, meaning a slight improvement in efficiency.

Copyright (C) 1996 Donald L. Klipstein (Jr) ([email protected])
http://members.misty.com/don/bulb1.html

He did have some interesting comments on end necking, sounds like it is alot more common on bulbs that don't run continous, and with some bulbs, soft-starting greatly increasing the lifetime. 

Ginseng, when your halogen bulbs blow, where is the filament usually blown, someplace in the spiral, or towards the end where it connects to the "standoffs"?


......

Here is the explanation usually offered, in another form:

Hello to Halogen
A halogen bulb works differently. It still has the same tungsten filament inside it as do the others, but here chemistry is employed in addition to physics to prolong its&#8217; working life.

Inside these light bulbs, there is a halogen gas (almost always iodine) present, mixed in with the argon or krypton. This new gas reacts with the vaporized tungsten that collects on the glass to form chemical compounds called metal halides. These then leave the inner surface of the bulb in a constant recycling process and return to near the filament where the increased heat breaks down the halide into its constituent parts. The tungsten molecules are now given to return to the filament, and the iodine molecules are free again to join up with any more ejected tungsten.

This is known as the halogen cycle. The reaction only works successfully on the glass itself though, rather than the bulb&#8217;s inner space, once the tungsten has condensed and will not take place if the glass is not hot enough. Therefore halogen light bulbs have to be smaller (which increases the heat); handmade of a special higher-grade glass known as &#8216;hard glass&#8217; or of quartz to allow them not to break at this extra high temperature.

Halogen bulbs cost more, but may have a lifetime of up to triple a normal light bulb of the same wattage, and at the same time be anything up to a fifth more efficient at producing light


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## jayflash (Aug 15, 2004)

Does anybody have a recommendation about the length of time a lamp must be on to insure a complete halogen cycle? It's been suggested that using a light for only a short (how short?) time will darken the globe. I'm not referring to the 
thermal stress of repeated power ups reducing lamp life.

Would 30 seconds of on time be sufficient? One minute, two? Any hard data on this? I didn't find any specific time mentioned in the lamp info that I downloaded, or did I miss it? Thanks for any help.


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## somelamps (Aug 15, 2004)

30 seconds is ok, the halogen cycle should be working at that time.

/ubbthreads/images/graemlins/bowdown.gif Somelamps.


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## somelamps (Aug 15, 2004)

-Jim Sexton WROTE:
So if the filament is running that hot, why doesn't it melt the electrical/mechanical wires which hold it in position? 

JIM SEXTON:
Halogen lamps use mollybden wires, mollybden supports has a high melting temperature.

/ubbthreads/images/graemlins/bowdown.gifSomelamps


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## mattheww50 (Aug 16, 2004)

Unless it is a very small lamp, 30 seconds probably isn't long enough. According to the GE Lamp catalog, the halogen cycle operates only when the tube wall temperature is between 482F and 1230F. The key caveat is the base, or seal temp has to stay below 662F to prevent premature seal or base failure. In other words the filament enclosure really does need to get HOT. Since many halogen lamps have an inner and outer envelope, the outer lamp may not need to get that hot, but absent that (as in typical quartz Halogen), the lamp envelope really does need to get that HOT!


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## js (Aug 17, 2004)

mattheww50,

Sorry to be so blunt, but you don't know what you are talking about.

1. The CCT and the actual filament temp are within 200 K of each other at the most in all incan tungsten halogen lamps.

2. Xenon and other inert fill gases reduce the rate at which the filament boils off. Period.

3. You can run a tungsten filament within 300 K of melting. As opposed to a carbon filament, which while it has the higher melting temp, boils off rapidly at MUCH lower temperatures than tungsten (2500 K).

4. A lamp with a fill gas with traces of a halogen does NOT blacken over time.

somelamps,

Thanks for the info, but I answered my own question in a post above. Also, most lamps do NOT use the molybdenum ribbons. The commonly used WA lamps do not, for instance. The need to use these comes when the lamp envelope is made of quartz glass, and not hard glass. The former has such a low coefficient of expansion that the glass/wire lead interface becomes an issue.

All of this stuff is in that PDF file which can be downloaded from the link provided above. I think that Osram Sylvannia technical bulliten is a pretty darn reliable and authoratative source. And if it says the fill gas reduces filament boil off, well . . . it does. Otherwise, why use it? Noble gases were used as fill gases BEFORE halogen cycle lamps, and precisely because--for whatever reasons--it reduced the filament boil off and thus allowed hotter running filaments.


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## NewBie (Aug 17, 2004)

Sometimes you'll find this material in bulb glass/metal seals:

Kovar


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## js (Aug 17, 2004)

Here are some quotes of interest from "Tungsten Halogen Low Voltage Lamps Photo Optics":

[ QUOTE ]
For an ideal "black body" (in the physical sense) the color temperature is equal to the true temperature. . . . Tungsten, however, is not a "black body"; its emissivity is less, i.e. the total radiation emitted is less than in the ideal case. One could say that tungsten is a gray body radiator. But even that would only be a half-truth, because in the short-wave region tungsten is a better emitter - though still not as good as the ideal black body - than in the long-wave (red) region. This variation of the emission coefficient has a positive effect on the radiation characteristics of tungsten in that its color temperature is higher than its equivalent true body temperature. In the region of interest for lamp technology around 3000 K, this amounts to 60 - 80 K.

An upper limit for the color temperature is given by the melting point of tungsten and the requirement for minimum lamp life and the operating duty cycle; it lies at about 3550 K.

[/ QUOTE ]

Thus, given that the melting point of tungsten is 3383 C = 3656 C, and that the CCT is within 80 K of true T, we have (worst case) 3470 K true temp for a CCT of 3550, which is 186 K from the melting point of tungsten!

And here's some more:

[ QUOTE ]
The fact that halogen lamps remain equally bright to the end of their life is not the only advantage of tungsten-halogen lamps. They also convert electric current to light more efficiently.

This works as follows:
-In conventional incandescent lamps the vaporized tungsten is deposited on the glass bulb. To keep the light loss as low as possible the bulb surface is large so that the absorbing layer is thin and widely distributed. As the bulb does not blacken in tungsten-halogen lamps, it can be very small.

-Because the bulb is very small, more expensive glass can be used; normally quartz glass.

-Because quartz glass is very strong and the bulb is small, the gas pressure in the lamp can be increased.

*-The higher gas pressure suppresses the vaporization of the incandescent filament to a greater extent.

-As the lamp has a small volume, economic considerations also allow the use of a more expensive fill gas such as krypton or xenon, which suppresses the vaporization of the incadescent filament to a greater extent than the usual lamp gas (nitrogen and argon)*

-A reduced rate of vaporization of the incandescent filament can either be used to increase the lamp life, or if the lamp life is unchanged the filament temperature cna be increased.

-A higher tungsten temperature not only means a higher color temperature ("whiter" light), but also greater efficacy in terms of lumens/watt.

[/ QUOTE ]

Emphasis mine.


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## jayflash (Aug 17, 2004)

Incans aren't dead yet.


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## KevinL (Aug 18, 2004)

Yeah, they'll be around. For a few bucks I can get hold of a P91 lamp that gives me an assured 200 EFFECTIVE lumens rather than bulb lumens (that means it probably has around 300 bulb lumens), no single LED can do that today. X-bins come close but not quite. 

Any info on how long we need to light the bulb till the halogen cycle starts? I hear something like 15-30 seconds in some other posts on CPF. The difference with LEDs is that I don't feel guilty strobing them on and off, or starting them cold, running them for a short burst and then leaving them to cool down again. When I do that to my incans I always have this nagging thought that it compromises bulb life.


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## AtomSphere (Aug 18, 2004)

is xenon bulbs very fragile? 

i mean when i drop my torch hard with a xenon assembly inside will it blow? hear this rumor somewhere


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## js (Aug 18, 2004)

KevinL,

If you read that publication "Tungsten Halogen Low Voltage Lamps Photo Optics" or whatever it is--long name!--then you will learn two things on this topic:

1. Even if you get tungsten deposits on the bulb surface from strobing your light, when you later run it for a good 5 minutes or more, the halogen cycle will clean it up, unless it is REALLY bad, at which point, who knows. So unless ALL you do is strobe, you should be OK as far as blackening the glass goes.

2. Unless you have a "soft-start" feature on your light (SF A2 for example) the frequent cold turn-ons will be likely to weaken the filament in spots because the halogen cycle returns the tungsten atoms to the filament, but not in the same place from which it boiled off, but rather to a colder spot. Thus the thinner, hotter parts of the filament, get thinner and hotter until--POOF!--no more filament.

Of course, if the filament is still hot from ten seconds ago when it was running, then this won't be as much of an issue, if at all.

Also, in modern tungsten halogen lamps, the halogen cycle is operating over all practical voltage drive levels, even the dim regions, so there is no concern about the bulb blackening due to continuous underdrive. Engineers have balanced the factors involved such that this is now a non-issue. According to that technical bulliten anyway.

So, bottom line is, I think, don't go crazy strobing your lamps, but if you do really need or want to for some reason, don't worry too much.

AtomSphere,

Depends on your definition of "fragile": dropping a non-shock isolated bezel incan from 6 feet onto concrete will almost certainly break the filament. But dropping from chest height onto most carpeted, or wooden, or vinyl w/plywood subfloor surfaces, is another story. I and other CPFers have reported from anecdotal evidence, that this is not all that likely to break the filament. The higher power lamps have thicker filaments and are less likely to break, BTW.

So, yeah, a "hard" drop will probably ruin your LA, but otherwise, it will probably be fine in my experience. These aren't as fragile as everyone always makes out.


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## paulr (Aug 18, 2004)

I hardly ever run any powerful flashlight for 5 minutes nonstop. I use small LED's that way, but bigger lights tend to be for much shorter bursts. For example, I used my PT Surge a few nights ago to spot some house numbers from the car. That meant it was on for only a few seconds at a time.


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## js (Aug 18, 2004)

paulr,

Yeah, I suspect a lot of people use their powerful incans this way. I am unusual in this respect: I often will run my incans for 30 minutes or more in one go.

So, you're a perfect person to weigh in on this subject! Do you find that your lamps blow before their rated life? Do you see some shiny gray-ish blackening on the inside of the bulb? Do you notice any reduction in brightness with time? What are your findings?


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## jayflash (Aug 18, 2004)

Hey there, Atom. I've dropped my TL-3, Scorpion, SuperSabre, Stealth, ProPoly 3C & 4AA onto concrete more times than I care to remember. This has happened with the lights on and off. My aluminum lights have dinged up heads and sometimes the bulb popped out into the reflector area. I never blew a lamp this way. Other times a xenon lamp blew when first turning it on, but that's unusual.

New lamps are tough but you can still find one that will blow when it's still fairly new. LEDs aren't foolproof either, BTW.


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## AtomSphere (Aug 18, 2004)

[ QUOTE ]
*jayflash said:*
Hey there, Atom. I've dropped my TL-3, Scorpion, SuperSabre, Stealth, ProPoly 3C & 4AA onto concrete more times than I care to remember. This has happened with the lights on and off. My aluminum lights have dinged up heads and sometimes the bulb popped out into the reflector area. I never blew a lamp this way. Other times a xenon lamp blew when first turning it on, but that's unusual.

New lamps are tough but you can still find one that will blow when it's still fairly new. LEDs aren't foolproof either, BTW. 

[/ QUOTE ]

good reply... i like when people tell from personal experience...


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## KevinL (Aug 19, 2004)

[ QUOTE ]
*js said:*
Also, in modern tungsten halogen lamps, the halogen cycle is operating over all practical voltage drive levels, even the dim regions, so there is no concern about the bulb blackening due to continuous underdrive. Engineers have balanced the factors involved such that this is now a non-issue. According to that technical bulliten anyway.

So, bottom line is, I think, don't go crazy strobing your lamps, but if you do really need or want to for some reason, don't worry too much.


[/ QUOTE ]

Thanks, I really should be reading that stuff, I'll go look for it later. I was always under the (WRONG) impression that once the vaporized stuff is allowed to cool, it sticks wherever it is and cannot move. I try not to strobe the lights as much as LEDs anyway but it's good to know that I can turn them on for short bursts if necessary. 

The part about the halogen cycle working properly across the entire drive range is very interesting information. I'm quite sure SF has thought of this. Some have advised to change out batteries in SF lights before the light goes yellow, in order to prolong lamp life. I usually change when the light dims noticeably, but it's good to know that the halogen cycle is still protecting the bulb. I compared a P60 that's been run down a few times to a brand new P60 (both on new cells), the old and the new lamps are pretty much identical with no blackening. Just my $0.02.


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## ViReN (Aug 25, 2004)

Aah... A whole load of Information is here... I think...Must Save & Bookmark this thread

ViReN


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## brightnorm (Aug 26, 2004)

[ QUOTE ]
*js said:*
...Also, in modern tungsten halogen lamps, the halogen cycle is operating over all practical voltage drive levels, even the dim regions, so there is no concern about the bulb blackening due to continuous underdrive. Engineers have balanced the factors involved such that this is now a non-issue. According to that technical bulliten anyway...

[/ QUOTE ]

That is really valuable information; makes me feel better about using (abusing?) my powerful incans.

Brightnorm


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