I recently installed a GE 250 Watt Lucalox Lamp, Type: LU250/H/ECO, and when I turn it on, it glows the normal white for a bit, and if I shut it off before the Sodium gets excited, the arc tube glows a Purple color for about 10-15 seconds.  No other HPS lamp I have ever used has ever done this.  Does anybody know why this happens?

My sylvania 70 and 100w HPS did this too, it may be the gas still energized.

The PCA arctube phosphorescence from the UV radiation from the xenon gas, after turning off. This happens with all HPS lamps and CMH lamps.

The PCA arctube phosphorescence from the UV radiation from the xenon gas, after turning off. This happens with all HPS lamps and CMH lamps.

This has never happened with any of my other HPS lamps.  None of my 100W or my Philips 250W do this.  This GE LU250/H/ECO is the only HPS bulb I have that does this.

All HPS, in all wattages, from all manufacturers that i tried do this

All HPS, in all wattages, from all manufacturers that i tried do this

If it s caused by the excitation from the Xenon, ouldn't be better said "all Xenon filled HPS" (the recent ones using higher Xenon pressures)?
The earlier lamps used way Xenon pressure in the fill, so such effect may not have been so visible...

I could see it in a 70W SON /I

Quote from: Ash on August 09, 2015, 05:02:22 PM

All HPS, in all wattages, from all manufacturers that i tried do this

If it s caused by the excitation from the Xenon, ouldn't be better said "all Xenon filled HPS" (the recent ones using higher Xenon pressures)?
The earlier lamps used way Xenon pressure in the fill, so such effect may not have been so visible...

That may explain it, but I just tried an Eye Ignitron, and it isn't as visible, but slightly visible.  the GE lamp looked like a blacklight.

I can try again the various lamps and take pics

Quote from: Medved on August 10, 2015, 12:32:38 AM

Quote from: Ash on August 09, 2015, 05:02:22 PM

All HPS, in all wattages, from all manufacturers that i tried do this

If it s caused by the excitation from the Xenon, ouldn't be better said "all Xenon filled HPS" (the recent ones using higher Xenon pressures)?
The earlier lamps used way Xenon pressure in the fill, so such effect may not have been so visible...

That may explain it, but I just tried an Eye Ignitron, and it isn't as visible, but slightly visible.  the GE lamp looked like a blacklight.

It does not have to be really just the Xenon, it may be other parts of the fill mixture or their combination. So as the lamp designs vary, that effect may vary among different makers/models as well...

I think that this would be occur also in penning start HPS lamps for retrofit MV lamps, as well as CMH lamps.

The Lucalox ECO lamps, just like some of Iwasaki's Ignitron Super series, use a different ceramic dopant in the arc tube vs all other SON and CMH lamps (the dopant is zirconium oxide, sometimes also with lanthanum).  This shows a phosphorescence effect and will continue to glow for some seconds or even tens of seconds if stimulated with shortwave UV.  The necessary UV wavelengths to excite the arc tube dopant are produced by the buffer gas fill of the arc tube, which explains why the effect is most visible if you switch off the lamp before allowing it to run up.  If you do let it fully run up, the sodium radiation is lacking in the wavelengths needed to excite the arc tube ceramic, and it will not glow blue after switching-off.

Why the change in arc tube materials ?

Does that play any role with ordinary SON / SON Plus lamps ? - As in significantly affecting structural integrity of the arc tube (explosion) or transparency (light output deprecation) ?

Interesting Max, since I am working much less now on CMH I didn't know they were also using such kind of doped arc tubes (of course the Chinese dope with practically every different element you can imagine to try and avoid patents etc, but few of them seem to bring any particular advantage in CMH, and most actually bring a very a considerable disadvantage in performance).  Are the ones you refer to using the standard Erbium-doped PCA material as found on Philips SON-Plus?

Ash - for sure the strength of an HPS arc tube decreases over time due to the process Max describes, but it is rare for this to lead to explosion since the arc tubes operate at such low pressure.  In case of a mechanical shock to the lamp, the arc tube can break though.  However the main reason for using one of the various kinds of doped PCA on SON-Plus and other longer-life or more highly loaded SON lamps is just to ensure better lumen maintenance, and hence a longer useful lifetime.