MH lamps turns white even before the halides start to radiate. Why? « on: October 13, 2012, 12:17:33 PM » Author: dor123
When I seen MH lamps warming up and seen their spectra using my CD-R, I have noted that after the mercury reaches optimal pressure, the lamps often loses their greenish mercury color and turns white before halide emission even appears on their spectra (Notable with Na-Sc lamps and rare-earth lamps without thallium). With these lamps, during this period of the white light + no halides emission, their spectra exhibits only the mercury lines, but with much more intense continum background compared to regular clear MV lamps. Why this is happens?
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	Re: MH lamps turns white even before the halides start to radiate. Why? « Reply #1 on: October 13, 2012, 12:59:42 PM » Author: Medved
~5x higher arc loading than in MV lamps...
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	Re: MH lamps turns white even before the halides start to radiate. Why? « Reply #2 on: October 13, 2012, 01:03:49 PM » Author: dor123
So why the mercury lines in MH lamps aren't seen wider to me, than in MV lamps? They still looks narrow to me, exactly as in MV lamps.
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	Re: MH lamps turns white even before the halides start to radiate. Why? « Reply #3 on: October 13, 2012, 01:14:56 PM » Author: Medved
With higher arc loading they do not widen (as does the Na D-line in the HPS), only the continuum rise up. Even in the UHP lamps the Hg lines are still quite narrow...
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	Re: MH lamps turns white even before the halides start to radiate. Why? « Reply #4 on: October 13, 2012, 01:27:54 PM » Author: dor123
I've seen a spectrum of a UHP lamp of a home media projector, and the mercury lines looked relatively wider, in fact so wide that they almost merged with the strong continuous background so the spectrum looked continuous. Also, the D-line in HPS lamps is also wider compared to LPS lamps.
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	Re: MH lamps turns white even before the halides start to radiate. Why? « Reply #6 on: October 13, 2012, 01:51:37 PM » Author: dor123
I've seen the mercury lines boardening in HBO and UHP mercury lamps. You can see this, in James Hooker's site .
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	Re: MH lamps turns white even before the halides start to radiate. Why? « Reply #7 on: October 13, 2012, 01:53:08 PM » Author: Medved
I mean there is large difference between sodium D-line (in HPS) versus Hg visible lines: The Sodium D-line correspond to the lowest level energy transition (from unexcited atom), while equivalent lines in Hg are in the far UV region and are nearly fully absorbed in the high pressure Hg lamp. The visible Hg lines belong to transition from already excited atoms to higher levels (the once excited atom is struck again before it radiate the excited energy in the form of a photon), so they tend to behave a bit differently, e.g. no selfabsorbtion - the remaining unexcited gas does not have available energy bands to absorb them and there is nearly none of the excited gas outside the discharge core; the D-line is, on the other hand, correspond to the first energy transition of an unexcited atom, so it is heavily absorbed by the unexcited abundance of the surrounding gas, what pronounce the widening effect (when the high spike is absorbed, the rest "appear" wider, as the shifted photons are off-tune with the cold surrounding gas, so are not absorbed anymore).
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	Re: MH lamps turns white even before the halides start to radiate. Why? « Reply #8 on: October 13, 2012, 02:57:38 PM » Author: dor123
The sodium D line is a resonance line and the visible mercury lines aren't resonance lines. But at pressures more than 10 atmospheres, the mercury lines should start to boarden as well. Even at 10 atmospheres with a high zoom, you can see the mercury lines boarden in a MV lamp spectrum compared to a fluorescent lamp spectrum.
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Please forgive me if my choice of my words looks like offensive, while that isn't my intention.

I only working with the international date format (dd.mm.yyyy).

I lives in Israel, which is a 220-240V, 50hz country.

	Re: MH lamps turns white even before the halides start to radiate. Why? « Reply #9 on: October 13, 2012, 04:23:26 PM » Author: Medved
The main broadening happen in similar manner as with sodium. But even with sodium, without the selfabsorbtion the main D-line would be so strong, the broadened radiation would be very weak compare to the main line. The main line would be still peaking from the "hill" of the broadened part. But as the main D line is absorbed by the surrounding cold sodium resonance, it isn't way as strong anymore, so only the broadened part remain. As there is no selfabsorbtion with the mercury, the main line blind all the weak broadened radiation. Only when the arc loading is so high, the brodened part grow up, it in fact become the observed continuum radiation. But as there is no selfabsorbtion, the original narrow peaks are still present in the overall spectrum.
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	Re: MH lamps turns white even before the halides start to radiate. Why? « Reply #10 on: October 16, 2012, 11:53:33 PM » Author: Globe Collector
I have been asked to reply to this topic. I don't really recall seeing a continuum background emission in Na-Sc lamps during run up except for Plankian hot body emission from the electrodes. The use of the high arc loading and Thoriated Tungsten electrodes, (because oxide activated ones would be attacked by the halides and resultant oxides would contaminate the arc tube) and low mass electrode design means that the electrodes attain a temperature in excess of 2000K and emit considerable amounts of light which is reflected around inside the arc tube. I have only ever studies the Na-Sc lamps at close range, I have not carefully studied the Tl-Dy 6500K type in detail yet.    P.S. Our Greek friend Iaonnis, had a very high resolution picture of the 437nm violet non-resonance line from a standard high pressure mercury lamp I think. The whole picture was only 2 or 3nm wide in bandwidth. Pressure and Doppler braodening and an inversion were visible, like what is seen in HPS lamps with the sodium resonance line over a much wider bandwidth. This broadening and inversion would be invisible to most of us with our low resolution spectroscopy.
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	Re: MH lamps turns white even before the halides start to radiate. Why? « Reply #11 on: October 17, 2012, 12:23:39 AM » Author: dor123
GC: I means that during run-up, after the mercury reaches optimal pressure and before the halides emission appears in the spectrum of the MH lamp, a continum slightly stronger than that of the high pressure mercury spectrum appears, which gives the lamp a pure white color, despite no halides emission appears. But the mercury lines don't looks wider than in a MV spectrum.
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I"m don't speak English well, and rely on online translating to write in this site.
Please forgive me if my choice of my words looks like offensive, while that isn't my intention.

I only working with the international date format (dd.mm.yyyy).

I lives in Israel, which is a 220-240V, 50hz country.

	Re: MH lamps turns white even before the halides start to radiate. Why? « Reply #12 on: December 09, 2012, 09:04:44 PM » Author: arcblue
No clue - but while I have observed MOST of my Na-Sc metal halide lamps radiating the clear mercury colour during run-up, I have seen some lamps that look about 4100K white continuously through their warm-up cycle (i.e. no noticeable colour changes, just increasing brightness). I don't know why. In fact, one of these lamps was a Sylvania 400w (probe start) and I have the same lamp myself, and it doesn't do this. It's probably like HPS lamps - almost all my HPS lamps have a slightly different profile in colour changing during warm up (and sometimes this also changes as they age). But that's what makes it interesting to me. I always like to see my HIDs go through that blue-green mercury discharge phase during warm up.
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	Re: MH lamps turns white even before the halides start to radiate. Why? « Reply #13 on: December 10, 2012, 07:27:29 PM » Author: BG101
On initial striking, my Na-Sc MH lamps have a number of bands in the red, orange, yellow green and deep blue parts of the spectrum (along with a strong line in the far red) which are definitely not just mercury lines, the initial colour appears white with strong, prolonged pink flashes during run-up. The cyan and near blue bands come up during the later stage of run-up. I don't notice prominent mercury lines at any stage. Now I have a basic spectroscope I can examine the run-up spectrum in detail, which is fascinating. BG
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