I commonly see some 'generic' cheapy mercury vapor lamps that have this problem. It seems to be quite common, as I see some pictures on L-G like this as well.



The new MV lamps tend tend have very short arc tubes compared to my Sylvania bulb. (Both were made in China)

Also, they don't start reliably on HX ballasts, can only start reliably in CWA ballasts. (Higher OCV)?

Shorter arctube, means higher loading per unit length, highly increasing the mercury pressure and the chances of the arctube explosions.

Higher arc loading does mean higher efficacy, it is one of the ways, how even low wattage lamps (125W and below) reach 50lm/W and even more for high wattage ones.
The quartz forming technology (due to MH's) evolved so, the arctube could handle the higher load, so it is natural evolution step to adopt it even for the MV's, I see nothing wrong with it.

Higher arc loading does mean higher efficacy, it is one of the ways, how even low wattage lamps (125W and below) reach 50lm/W and even more for high wattage ones.
The quartz forming technology (due to MH's) evolved so, the arctube could handle the higher load, so it is natural evolution step to adopt it even for the MV's, I see nothing wrong with it.

Medved: If this is the case, why i don't see wider mercury visible lines when i check the spectrum of a modern low wattage MV lamp with my CD-R?
With my Philips ML 160W, i also don't see wider mercury lines than usual.

However, why doesn't start as reliably on HX compared to on a CWA?

The lamp have probe only on one side, what mean in one direction it have lower voltage.
The HX ballast give the same OCV, regardless if the lamp operate only in one direction, so for the unfavored direction the residual ionisation in the arctube (from the previous half cycle) should be enough to restrike the discharge.

But the CWA uses series capacitor, what is charged by the (initially) rectifying lamp, so for the unfavored direction it provide higher voltage to strike the arc.


Second difference: The specified minimum ballast OCV for MV's is lower for lag HX than for lead ballasts. This could be the result of the CWA not able to build up any significant current, unless the discharge could be established in both directions (due to the same capacitor effect), as well as the higher and more energetic voltage for zero cross restrike with lag HX.
These effects  may have been more important for the older MV's, but are not as much for the newer ones.

Well, I do not say this is the only reason, these are only explanations, that came to my mind.

@dor123: Shorter arc with the same power clearly mean higher arc loading, it is simple math...
But is the spectrum varying so much? The difference in arc loading is no more than ~30%, while I do not believe this would create so huge difference in the spectrum (compare to the accuracy and resolution of the CD acting as a spectrum analyzer).
Moreover European lamps (designed for higher efficacy) had shorter arc tubes than the US ones (designed for longer life), even for the same rating, so when unifying the higher efficient style designs, for US guys it mean the new lamps have shorter tubes then they are used to.

I gues that the new lamps have shorter life

The same (if not more from the higher loading - dont know) amont of blackening (or whitening) is supposed to be created, but is spread on smaller area of the inside of the arc tube now. And it does not have a significant section of length which is farther away from the electrodes and continues to emit brighter light as the arc tube is losing transparncy mostly in the ends

Well, that is a result of an engineering compromise: Either you get longer life, or higher efficacy. Maximum you may do is balance out some compromise. And criteria for this balance moved over the years from the life towards the efficacy...

The blackening was suppressed by the whitening agents, so heavier coat does not mean as high lumen loss, at least till the whitening agent is consumed. So it was not as big problem, so the whitening agent consumption and the quartz integrity are the two aspects limiting the life.
Whitening agent may be dosed well and the quartz improved, so allowed smaller, higher pressure arctubes to be made for the same rated life.

Wont the new lamps have faster light output drop right away, driving them down to the same light output as older mercury lamps after a fraction of the time (so making no sense in the arc tube shrink), due to faster loss of transparency of the arc tube ?

If that is a factor, then I would be convinced the arctube size is on the optimum (so the highest average lumen output)
The ones, who design these lamps are no dummies (include the Chinese; they only design with the cost being more important).

I think along another line : They made a 50Lm/W mercury lamp to get around a ban, but if after 1000 hours this lamp drops to <30Lm/W it is worse than the older "inefficient" mercury lamps....

The efficacy is better over the whole rated life. Don't forget the newer arctubes are thinner, so the sputtered material does not reach that far (it remain around the electrodes), so the lumen maintenance is not that bad.


Don't underestimate them, the design of their products is usually not that bad, taking into account the limitations imposed by the requirement of cheap production. My impression is, than with the same (aggressive) cost objectives the Chinese products are frequently designed way better than their "western" counterparts in the same price category (and I mean corrected for the labor cost difference).

The problem with Cheepeese lamps (and not only lamps, but nearly all products there) is the terrible discipline in the production facility, mainly the tendency of the manufacturing supervisors authorize (or even order) to skip "unnecessary" quality checks and making other shortcuts in order to boost the production figures. Results are defective products being sold (then these failing very soon), totally ruining the reliability of otherwise good designs and mostly even quite skilled workers.

When the manufacturers began to use smaller arctubes for their mercury lamps?