I have noticed this happening on more than one of my lamps. For ten or fifteen minutes after lighting, the lamps put out a bright white light. However after this time the output gradually dims to a warmer orangey light which then persists as long as the lamp is lit. Has anyone else experienced this? What is the explanation? For background, this happens with three different types of paraffin, but all using the Tilley X164 mantles. Increasing the pressure has no effect.
I noticed when measuring light power that most lamps increase cp by about 10% after running for ten minutes. I assume it generally takes that long for the generators and burners to reach a steady temperature. There is no doubt that changes occur during that first ten minutes or so. Quite why I don't know and from measuring them mostly I saw an improvement rather than a deterioration such as you describe but it has to be related to that gradual start to optimum burn. ::Neil::
Pricking has no effect. The light output after falling is acceptable but not a white light. The vaporisers I have tried are both new old stock with brass knurled collar. The burner on one lamp is a Tilley original and the other is from Julian. The only common factor seems to be the mantles. I do have some others which I shall have to try, but I am reluctant to destroy the Tilley ones unnecessarily.
@R100 I’ve not had that problem generally —only with a dodgy generator or burner. I use a wide variety of mantles for testing and in my field and camping Tilleys. In my “show” Tilleys I usually use Basecamp or Tilley mantles. I’ve not seen light dulling as a pattern. Cheers Tony
I really can’t see how they could have a bearing on it, it’s the fuel/air vapour output dropping off that’s the issue. I suspect the vapourisers/prickers NOS though they may be. Although hard to see by eye (though not impossible) it’s possible to check that a pricker tip emerges by feel when the control is operated. I’d make sure that’s happening. NOS doesn’t always signify perfect and a defective pricker function is likely to be the fail point. Protective grease for storage creeping inside congealing, then melting and compromising output by partially blocking the jet during the burn is a possibility. If it were just one lamp doing this I’d suspect mechanical wear in the pricker control mechanism, failing to raise the pricker sufficiently to clean the jet reliably. Odds of that lengthen with multiple lamps. Other thing I’d check is that the vapouriser sealing washers are on spec. Some from ebay sources are woeful (too thick) and hinder the pricker function by increasing the jet tip to pricker operating cam distance. John
But what R100 is describing is the lamps starting out bright and losing light intensity during a burn, not variation between one mantle and another from the outset.
There is no possibility there is a very slow air leak, is it? Does it reach a point where it stops dimming and just stays that way? If so, that would seem to eliminate an air leak. If it keeps dimming gradually then it's possibly an air leak...
I did notice a similar effect on many an occasion, @R100 . Exactly as what you've described. However, its not so much of a falling output. I believe there's nothing wrong with the lamps in your case. From my observation on such, it has to do with the subtle change in the output wavelengths of the visible light. When you startup a cold lamp, only the mantle is really hot enough to be incandescent. Usually, the mantle compositons are tailored as to emit light with wavelengths mostly towards white or yellowish-white when heated sufficiently. After 10 or 15 minutes into the burn, the adjacent parts closest to the mantle, the ceramic or metal burner cap in this case, will be hot enough to glow red-orange-yellow. This glow has more reds and orange wavelengths in it. Besides, the hot gases around it would actually appear reddish-orange. So in overall, the emitted light from the mantle would appear less white than during the initial minutes of the burn because the percentage of red and orange wavelengths has increased. Yes, I'm referring to the altered spectrum caused by the incandescent burner cap. Just as example, if you allow the lamp to burn long enough without the mantle attached, you'd notice that the otherwise pale blue flame will start to have some yellows and orange in it due to the incandescent burner cap.
Hi Myn, That is an interesting explanation and I'm relieved someone else has noted this. In my case however I was not relying just on my eyes , although it was visual observation which gave rise to the question. I measured a distinct fall off of light using a light meter. The fall off was in the order of 2EV which was accompanied by the distinct colour shift from almost pure white to a pale orange. My wife sits near one of my table lamps and reads by its light, but after the light drop she finds it difficult to do so. It is strange that no-one else seems to have noticed it.
You could put a light meter app on your mobile if it supports it. As you are looking for a change in light the absolute reading is less important. It may not capture any change in colour but it should tell you if the actual light output has changed ?
@Fireexit1 No need of an app on my phone as the light meter I used was a professional instrument. As stated in my last post the light fall off was about 2EV (exposure value) or two stops on a camera.
I am not an expert or physicist but I think that EV is not a linear scale like lux or lumens, however it is showing a drop so it is "proven" to be happening. I also do not know what effect the balance of the light would have on EV, so MYNs theory is not out of the running. I would still favour the idea that something is dimensionally changing and permitting ingress/egress of air or fuel and changing the mix or some sort of minor blockage - I have also seen this effect on a coleman 214 of mine but pricking seems to solve it. I also don't think the mantle is the culprit. Fascinating.. If you have examples where one lamp does it and one does not and the parts are interchangable it might be worth swapping things about to see if one or the other is the cuplrit ?
There is a detectable change even from my visual observation. From my own experience on this, I was using purely thoria mantles which, have whiter(with slight green tinge) light emissions. If the light has more greens or blues, it'll measure higher eV values as well. It does not necessarily mean the overall quantity of light has actually reduced. But then, our eyes are most sensitive for those towards the green wavelength. In effect, we'll perceive it as output reduction anyway. There are probably more explanation to the why there should be a shift in the frequency range of the emitted light. I'm not sure if heating the mantle compositions beyond a certain temperature range would cause less emission of blues and greens on the wavelength vs temperature curve. I would mention that this might not fully be a purely blackbody radiation phenomenon. Candoluminescence that is. Besides those, I'm also aware that, if the entire burner and mixer assembly has been heated sufficiently to a certain point, chances are, the combustion air as well as the pre-mixed fuel-air might be having lower oxygen densities in them(due to thermal expansion). I cannot deduce if that is of any significance but I have a hunch that it might actually reduce a little of the mass fuel-air throughput. Or would it cause a shift away from the optimum fuel-air ratio. If any of that should be the case, then it won't be surprising that the observed light output would drop as well.
As hinted by @Fireexit1 , there is a difference if you're measuring the light with a luxmeter or a spectrometer or something else. The general luxmeter will measure and provide an average reading on the light falling within its aperture. A spectrometer can provide the measurement of the different wavelengths and display in various units. eV for example, but that's the energy of the specific light spectrum. Its higher towards blues or ultraviolet. So if there are more reds or infrared, the total eV would be lower. Assuming the amount of photons are the same for both cases.
Ow! My poor brain cell is starting to hurt. I have just noted the same effect on an X246B, albeit nowhere near as pronounced as my table lamps. There does seem to be a pattern forming (for me at any rate) in that I am tending to think that this is a physical effect of all lamps, except that we don't notice in it most situations. My table lamps are used in a large and deep bay window at night with just those lamps for illumination. The surface on which they are placed is white and on three sides they are surrounded by off-white blinds. This appears to me to be the near perfect environment in which to see the light drop off. My other lamps are mostly used outside, either as portable light sources or at dusk in a static position with constantly deteriorating natural light. In those circumstances, I have never noticed any drop off.
Well its certainly noticeable to me @R100 . It baffled me somewhat but I've never seen it in a discussion before. I do not discount that our eyes can sometimes play tricks on us. If they're exposed long enough to the mantle light, we can sometimes perceive different colours or tints from the same source. The only way I can think of to test some theories is to setup an apparatus to direct the blue flame from a steady blowtorch on a spreaded-out mantle without it being attached to the burner cap. Only the mantle will be heated to incandescence and nothing else. If the colour of the emitted light changes after a while, then we know the theory can be shelved.
i reckon that your vapouriser/generator/jet is on the way out, maybe dead, depending upon how orange the light has gone...i have experienced this on lanterns where the generator was nearly dead(as in the jet orifice had enlarged) the next stage was orange light with a kind of a flame halo around the top of the mantle, visible through welding glass/sometimes visible to the naked eye....The two keys for me saying this are...(1)The change to an orange flame(rich mixture, undertemperaure). (2)That the lantern was bright first(jet nozzle hole cold) --as the lamp heats up to working temperature the nozzle hole expands, this causes the overrich mix. Blessings, RxR
Thanks, but this is not likely as the issue peresists with two different lamps. Swapping the vaporisers for NOS or new versions has no effect. Neither does swapping over the burners and galleries.
I have seen pressure leaks where anything over a certain pressure does leak, but once it drops below a threshold the leak stops. This normally involves a seal which kind of acts as a pressure limit valve would. Clutching at straws, here but experience has taught me that sometime the silly things are the things.. (some have even accused me of making a career of it)
I welcome all these suggestions and thanks to anyone who can offer more. @Fireexit1 If that was the case, then re-pressurising would temporarily solve the issue but alas, it does not.
Cracked it! The problem is with the fuel. I have been using a highly refined low sulphur paraffin which, whilst it has little smell, it does produce an orangey light after burning for ten minutes or so. Having found no other reason for the issue, I realised that the lamps which I had not filled with this fuel did not behave in this way. Drain the tank of the problem lamp and refill with common or garden paraffin and all is well. Why the heck I did not consider this earlier I can't explain. I'll put it down to stupidity.
Well done that man ! - when you say "highly refined low sulphur paraffin" do you mean "indoor lamp oil" or similar ? I only ask as I have some and was wondering how it would work in a pressure lamp.
I tried indoor lamp oil a while back. It does not work well. It gives nothing but a poor dull orange flame. It makes me think that this super refined paraffin is similar to indoor lamp oil.
