A 10-Year bulb.

X-CalBR8

Flashlight Enthusiast
Joined
Apr 14, 2001
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Location
TN, USA
Here is an idea that I can't even begin to fathom why it hasn't been done already. Maybe you guys can help me figure out why this hasn't happened yet. Take a standard incandescent bulb, that uses a vacuum to keep the filament from burning up, and instead of using a vacuum, fill it with glass or some kind of epoxy just like a LED bulb is filled. Doesn't this make perfect sense? Everyone claims that the reason an incandescent bulb burns out over time is because it doesn't have a perfect vacuum and some air eventually gets to the filament causing it to burn up, but if it was filled like a LED, then it should never get air to it and, consequently, almost never burn out. Why can't we have, for instance, a halogen bulb that would last for 10 years just like a LED? Imagine the brightness of a Surefire but with a bulb that wouldn't burn out for years. Have you guys ever discussed this before? What are your thoughts on my 10-year bulb idea? Can this be done easily, and what would be any potential downsides to trying this? LOL, everyone else mods the flashlights themselves, but leave it to me to be the one crazy flashaholic here to try to do a bulb mod.
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Doesn't this make perfect sense? Everyone claims that the reason an incandescent bulb burns out over time is because it doesn't have a perfect vacuum and some air eventually gets to the filament causing it to burn up, but if it was filled like a LED, then it should never get air to it and, consequently, almost never burn out.


Er....sorry- no, it won`t work. Encasing the thin tungsten filament in glass or resin would just conduct all the heat away and it wouldn`t glow. The reason a bulb lights and extinguishes so quickly is that the amount of metal in the filament that has to be heated is so small and takes very little time to heat it all to white hot (and hence produce light). Similarly when the power is shut off it goes from white hot to cold in seconds. Encase it in glass and you have greatly increased the mass that needs to be heated. It may eventually start glowing but the glass would melt long before it got white hot. The temperature of a halogen lamp filament is hotter than the surface of the sun! Glass melts at a much much lower temperature than Tungsten, which has one of the highest melting points of any metal- many thousands of degrees.


As for why bulbs fail, well I do sort of know this (there are other ways than just air getting in that causes it- and often most bulbs today are inert-gas-filled not vacuumed) but a better explanation than I could offer I believe is on Don Klipstein`s excellent web site and you can see it here.


Sorry to drown your hopes like that. Believe me if it could be done, it would have been already! I`d love a 10-year Surefire xenon-halogen bulb too (and hows about some 10-year-runtime 123 lithiums too while we`re at it
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) but it just won`t happen I`m afraid. LEDs are definately the way forward in that world of long life solid light sources.


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Well, looks like back to the drawing board for me.
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Thanks for the info Chris. That will give me even more to ponder. Perhaps something that would give off light at a much lower temperature. Heat in a bulb = inefficiency, anyway. It would be kinda neat to see a LED alternative. Right now there is just nothing that really compares with LEDs in many respects. I also think things will be revolutionized once a LED is made that produces white light without the need to dope it with phosphorous. I'm sure the addition of the phosphorous must dim the LED and, as we well know, you can almost never get that perfect white without a little bit of a blue ting in current generation LEDs.
 
As I understand it, incandescent lamp technology is about at it's limits, so only slow improvement is possible.
Are there any new materials on the way, or new gas mixtures ?
There are some new glass / ceramics compositions, which might help. Possibly even a new super plastic could turn up.
How does the improvement curve look, for say the next 5 years ?

And how far off is a really powerful LED, that is, what can we expect in 1, 2, 5 years time ?

Since I'm asking those topic related questions, can someone please explain quite why a led won't project further than the 80-100' or so telephony says the Ledcorp Mag 3D bulb achieves ? Is it just a matter of the internal reflector being too small, or the fact of relatively low output ?

A very befuddled

Lite-lover
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My mate JDH would be able to tell you more about the future of incandescent lighting, assuming the manufacturers have not sworn him to secrecy in which case he won`t even tell me. I don`t know much and am not sure which of what I do know, I can tell here.

And how far off is a really powerful LED, that is, what can we expect in 1, 2, 5 years time ?



Well.....also not sure how much I can say at the moment but I have here a chart (produced by the very same JDH) that predicts the improvements in LED technology based on the advances LumiLEDs have made so far. I`ll ask if I can post it (or something similar), that would give a good idea of what to expect. It is not going to happen overnight but within (most of) our lifetimes we should see LEDs take over from incandescents in the home, street, car, well everywhere really.


...can someone please explain quite why a led won't project further than the 80-100' or so telephony says the Ledcorp Mag 3D bulb achieves ?

It is just to do with the fact that it isn`t very bright. One Nichia LED can only shine so far. One Luxeon Star 18-lumen LED focussed sharp enough (through a lens of some sort) would shine much further.

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Chris, ask what you can actually say, please. Can you talk about any improvements in the glass envelopes, inref to the new specifications of glass. What is the best transmissivity (?) of the current glass used ?

lite-lover
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The total transmissivity of stadard lamp glass is well over 99%, and it is made as thin as possible to keep this value high. About 3% light is reflected from the inner surface, but the light lost is not as much as this because what is reflected simply travels across the bulb and the bulk of it passes out the other side.

Ordinary bulbs use a very pure grade of soda-lime glass similar to window glass. Newer tungsten halogen lamps are made from quartz glass instead (which is >96% Silica) or a glass called aluminosilicate. These do not contain impurities which would interfere with the operation of the halogen chemicals inside, and they enable lamps to burn brighter for longer. Quartz has been used for decades though and it is unlikely it will be superseded for mass production lamps for many years. Some work has been done in making lamps with translucent ceramic bulbs which are capable of operting at higher temperatures and greater internal gas pressure, but really I think that their cost is so high for the small advantage they give, that they will not leave the research labs.

Incandescent lamp technology does have phenomenal scope for further improvement, but at present there are cheaper ways of developing new light sources on other technologies so the filament lamp is not really progressing much. Perhaps the easiest way to improve incandescent is to capture the wasted heat and turn it into light - several lamps employ a coating on the glass which lets light pass through, but reflects heat back to the filament. That makes the filament hotter and glow brighter for no extra power input. Its easy to get 30% more light this way and there are a severla lamps of this type already on the market.

To go any better, you have to look to filament materials other than tungsten. Silicon carbide and Hafnium carbide are two leading contenders, both to be used in slightly different ways. These materials can burn brighter than tungsten and don't evaporate away (burn out) so fast and also they produce far less heat for the same light output. No products like this are available yet but you can expect to hear more on the development of these probably within 5 years time or so.

Chris - feel free to show that LED graph on here. I would do it myself now but I can't find the file so if you still have it, please add it on.

Best regards!

James.
 
Thanks very much, JDH, that's terrific. Looking forward to seeing the LED info too.

I'm glad to hear that there is still a lot of scope for incandescents to improve.
So what is the probable limit of improvement, you suggest about 30% so far using glass coatings.
With Silicon or Hafnium carbides as filaments, how would outputs be raised %wise ??
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I didn't realise that the glass envelope allowed as much as 99% transmissivity. My understanding was that 7% loss of light per each glass layer was inevitable.
For instance, over on the SureFire board, PK recently pointed out that the M3 Pyrex lens, when specially coated on the inside, allowed ~95% transmission.
Are the rules different for the lenses of torches ?

Lite-Lover
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feel free to show that LED graph on here.....

OK will do

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Forgive the reduction in quality- it was all nice and printer-friendly before but it was too big to fit on the screen so I shrunk it to 25%.


These are laboratory figures and even though it looks like the 100 lumen LED has just about been acheved, it will be a few years yet until we get to hold one in our hand and dazzle unsuspecting people with it. The 18 lumen LED is a matter of a few months (or maybe even weeks) away but as you can see, if LED technology stays on course, we might be lighting our homes (or at least our streets) with single-LED bulbs in as little as 15 years!

Makes you think doesn`t it- look out incandescents!

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Thanks Chris - the graph looks quite incredible, and also quite credible in the assumption of an increase like that.
(From the little I know of statistical presentations.)

Yeah, it seems unarguable that whatever the rate of progress, LED's will take first place in the relatively near future.

So will incandescents still have uses as long-throw beams, or for focusable sources ?
Or will they just be collectors pieces ?

And what will happen to the sales figures of battery manufacturers ??

Lite-Lover
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(Wait a moment - isn't Chris M. a lightbulb collector !! - is there a conspiracy theory coming alive here ...... )
 

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