I'm thinking it's pretty unlikely the tube walls can be totally UV-opaque, so this strongly suggests the tube does not use a phosphor that requires UV excitation. That leaves direct excitation by the AC field, or excitation by electron impacts.
I think you are wrong:
- I have a similar looking lamp but with electrodes. I can clearly see a bluish light from the area around the electrodes like in a normal fluorescent tube.
That's with mercury vapor. Spectrogram for mercury:
That's high pressure mercury, but much the same for low pressure. Lots of UV, some peaks in the visible range, so you can see a bluish glow in the gas.
- A UV-C lamp does not produce the slightes amount of green night. Neither does a normal white flourescent tube give any light output when held next to the UV-C lamp. This confirms that even the thin glass wall absorbs the 254nm emitted by the mercury vapour completely. Otherwise a protective screen would be necessary around every fluorescent tube.
However the phosphor layer is completely UV-opaque. No extra shield required. UV-fluoro tubes like in EPROM erasers are exactly the same except the phosphor is omitted.
josem Thanks, those are very interesting.
This is getting more and more fascinating. There are several details in those patents that are ... curious.
A minor detail is their term 'Xenone gas'. I can't find any reference suggesting this is not plain Xenon, so it's probably just patent-drone bullshit jargon.
Much more interestingly, there's something wrong with their description of the operating principle of these lamps.
They get it right for mercury fluorescent lamps, stating:
"Fluorescent lamps of the type typically used for household and office lighting have internal electrodes. Heating the electrodes causes thermoionic emission of electrons. Providing a high voltage from one electrode to the other causes electron flow between the electrodes. The electrons then excite mercury atoms. The excited mercury atoms release their acquired energy in the form of ultraviolet radiation. The ultraviolet radiation excites a phosphor coating on the interior of the lamp, resulting in emission of visible light."
But for these lamps, take this example statement:
"When an RF voltage of 20 to 100 kHz and 1 to 2 kV is applied to the two belt-shaped electrodes, discharge of xenone gas is generated in a discharge space in the bulb in a direction perpendicular to the bulb axis, and the phosphor film on the inner wall of the bulb is excited to emit light. At this time, since the discharge gas is xenone gas not containing a metal vapor such as mercury vapor, the phosphor film is efficiently excited by exciting light (147 nm) of xenone gas to realize a high luminous intensity."
What?! What is this 'exciting light (147 nm) of xenone gas'? Assuming they mean Xenon (and since it's an inert gas that doesn't like to bond with anything else including itself, what else could it be), then electrically excited xenon gas should produce the typical xenon spectra. Which is this:
Point is, Xenon has a lot of visible emission, not much UV. If there was Xenon in this tube and it was being excited to photon emission by the electron motion, it would be emitting visible light. More than UV. It would definitely be visible.
So that's problem #1 with the patent.
The next one is the 'striations' they mention. Yes, this tube has the serrated electrodes the 2nd patent mentions, as used to stop the striations wandering. But... think about it. If the tube is operating by current flow exciting the gas, which emits UV, and the UV excites the phosphor, how can striations in the bulk gas current produce fine striations in the light emitted by the phosphor? The gas ions would emit photons in all directions, so the effect should 'blur out' by the time the photons reach the phosphor on the walls.
Their description doesn't make sense.
On the other hand, where electrons impinge on the walls certainly can be confined to sharply defined regions, under some operating conditions.
I'm wondering if they deliberately obfuscated the mechanism, or if they simply made bad assumptions based on old style fluro-tube mechanism? It's very suggestive that they nowhere mention Birkelund filaments/currents, which are the fundamental process causing non-uniformity of the current through the gas. It's also true that plasma physics is very little taught anywhere, and has some very counter-intuitive behaviors. Perhaps it's possible that the people developing these tubes simply didn't understand how they work? Notice the amount of purely experimental fiddling they mention in the 2nd patent.
About the photocopier type. I was kicking myself that I didn't make a note of the model, and have since thrown out most of the case. But on checking, the case piece with the model sticker was still in the pile to be binned. The unit was:
Sharp Corp. Digital Copying Machine AR-201.
The inverter PCB says: USHIO PXZ170E1
There's no marking on the tube itself, but the attached connector has: USHIO UXFL-08YG37D
Oh, and dates in the machine's service card say it was in use from 2004 to 2009.