Today, at the very end of their official history in the EU, all mercury vapour lamps seem to be manufactured as neutral white to cool white (3500K to 4200K). This is true both for known brands and China manufacturers.

As far as I can remember, in the 1980s, the colour temperature of the mercury vapour lamps was somewhere above 6000K (i.e. daylight). These lamps still can be found at the very rare places in our country (Czech republic) - usually old fixtures in the factories etc.

My questions:
1. When did this change occur?
2. What did this change (chemically)?
3. Did it go together with increasing the efficiency of these lamps?
4. Am I correct that nobody produces the ~6000K mercury vapour lamps today?
5. Is it possible to get them anywhere?

I did an internet research but I'm a bit confused. There is a lot of contradictory information on this topic.
Thanks.

You could be thinking about either clear mercury lamps or lamps that only have a diffusion coating instead of a phosphor coating. Both are still made, although not readily available in Europe.

A typical clear finished mercury lamp, have a 5900K color temerature and a color rendering index of Ra8=16.
To lower the color temperature, and to improve the color rendering index and the lamp spectrum which is lack of red, a phosphor applied to the outerbulb, which produces at the red wavelength.
The first phosphors was Zinc Cadmium Sulphide, which its yellow body coloration, gave the lamp a greenish hue.
Later, Magnesium Fluoro-germanate was popular, which improved the color rendering, and lowered the color temperature, but as it also filtered part of the blue mercury lines, the light is still slightly greenish.
The modern phosphor is Yttrium Vanadate, which because of it white body color and high red efficiency, lowers the color temperature to 4000K and increases the color rendering to 40-49 and increases the lamp efficiency.
There were mercury lamps with multiple phosphors such as Philips HPL Comfort, Sylvania H100/N Warmtone, Westinghouse
H400/R Beauty Lite.

I think quite a good description of the MV history is on James Hooker's www.lamptech.co.uk.
But with that you should not forget, not all breeds were manufactured/available here (behind the "curtain"), but still what was used here matches some of the types described there.

As far as I remember, clear lamps were not used here since 60's at least.
But the used phosphors were not all the time aimed just at increasing the red content, but for quite a long time to just boost the efficacy (the aimed use was just the street/industrial lighting, so max lumens / don't care as much about the color), mainly with the Yttrium-Vanadate. There depend on the doping elements, what will be the emitted color, it could be anything between ~3400..6500K, just a matter of mixing the phosphor dopants. As the primary aim was for the efficacy, it was mixed to get quite strong blue/green, so less of the red relative content (the red has to radiate with quite significant radiated power, but it adds quite little lumens and on the top of that means losses related to output vs input photon energies). Therefore the emitted light was rather high CCT greenish, later more white hue.
The higher quality lighting tasks were moved on fluorescents and mainly incandescents.
In the "western world" the MV's were developed as well for higher light quality use, so offered the warmer tones. And it was only quite later, when the warmer tone lamps reached the street light poles.

And other effect is lamp aging: When comparing older and newer lamps, you can not prevent the actual comparing of heavy worn lamps with fresh ones. As the arctube ages, it starts to block the light going out. But it starts blocking the shortest wavelengths first. And the shortest wavelengths is the UV, which is normally utilized to generate mainly the red part. So missing UV from the arctube means missing red from the phosphor, what means higher CCT of the final light mix.

Thanks for the interesting link.
Yes, I can remember only the coated lamps (I was born in 1975). I think, most of them were Tesla RVL-X.

The warmer colour temperature vs. energy efficiency seems logical. This is also true for LEDs.

As for the clear lamps - is the UV just discarded? The outer bulb must block it to prevent sunburns. According to Wikipedia, the borosilicate glass is commonly used. As the conclusion, the clear MV's have worse efficiency than the coated ones?

A typical clear finished mercury lamp, have a 5900K color temerature and a color rendering index of Ra8=16.

You meant the lamp at the end of its life? Is the colour temperature really changing during the lamp lifetime?
I thought that the lamp is rather greenish at the end but the colour temperature does not radically change from warmer to the cooler one. But I'm probably wrong.

Thanks for the phosphor history.

Yes, the DX coating actually increases efficiency, in addition to raising the CRI and lowering the color temperature. For clear lamps, the outer bulb simply converts the UV to, I assume, heat.

You meant the lamp at the end of its life? Is the colour temperature really changing during the lamp lifetime?

By "clear finished" he meant just a clear lamp, not a lamp at the end of its life. If my knowledge is correct, clear lamps don't change color temperature as they age. As DX lamps age, however, the UV output of the arc tube diminishes, so the phosphor output (which is red) diminishes as well, turning the final light output a sort of yellow/green color.

Welcome here, by the way. 

Quote from: dor123 on April 07, 2014, 07:22:58 AM

A typical clear finished mercury lamp, have a 5900K color temerature and a color rendering index of Ra8=16.

You meant the lamp at the end of its life? Is the colour temperature really changing during the lamp lifetime?
I thought that the lamp is rather greenish at the end but the colour temperature does not radically change from warmer to the cooler one. But I'm probably wrong.

Thanks for the phosphor history.

I meant the when the lamp is new. Clear mercury lamps have a greenish light because of the lack of red, and the fact that the green spectral line is more prominent than the rest of the visible mercury lines in the spectrum (Two yellow, blue and violet lines).

You meant the lamp at the end of its life? Is the colour temperature really changing during the lamp lifetime?
I thought that the lamp is rather greenish at the end but the colour temperature does not radically change from warmer to the cooler one. But I'm probably wrong.

Here one must keep in mind that for such lamps with a non-continuous spectrum only a most similar colour temperature can be quoted. And I think this no longer makes sense at all if the output of a lamp lacks the red range altogether. (The same goes for HPS lamps of course.)

In summary the story is such that the introduction of the yttrium-vanadate coating for the first time brought a significant amount of red output to MV lamps, resulting in a light with a most similar colour temperature of 4000 K, very similar to the "cool white" breed of FL lamps. Earlier it was mostly a combination of yellow, green and blue lines. On a worn lamp the shortest ranges are particularly missing, both the visible blue lines and the UV that "lits" the phosphor (in the case of yttrium-vanadate in red, as can be seen immediately after switch-on), thus their remaining output has a distinctive green hue.

This ties in with my memory of mercury vapour street lighting, they had a distinct blue tint to them and I was disappointed to find that the modern lamps are a much warmer colour, at least when still fairly new. I'd love to get hold of some vintage MBFs with that lovely daylight colour!


BG

Lamp efficacy or efficiency is normally measured for the "visible" part of the spectrum. Naturally, when you convert UV wavelengths (below 400nm which are not visible), to visible light (red @ 625nm) you increase the lamp efficacy. Clear mercury lamps were PERFECTLY suited for such a boost in efficacy and in color correction by simply adding phosphors. In short time, the correct phosphor was found.

An aged mercury DX coated lamp beyond it's rated life, MIGHT appear bluer due to faded/lost phosphors.

^^ It is more the arctube blackening and not as much the phosphor degradation, what is responsible for the flux and color degradation beyond the end of life. The thing is, on many places they were not relamped at that time (although with MV, this is excellently predictable, when it happen), but that was maintenance and not lamp issue...

I wanted to create a photo comparison but it's rather difficult to catch it with a digital camera (even with colour correction fixed and manual exposure), so rather in words:
When comparing common Philips HPL-N (Made in China) and Tesla RVLX - (both new and fully burning) - to a triphosphor fluorescent 6500K, I'd say:

HPL-N: Is much warmer, pinkish, makes white painted wall something between pink and yellow, makes office paper light magenta tinted, makes a LCD screen look greenish.
RVLX: Almost the same as 6500K fluorescent, very slightly greenish, "something" is missing but natural, does not tint the LCD screen.

Conclusion: Even both tested MV are yttrium vanadate coated, you can very easily tell the difference. The manufacturing process has changed. The old MV colour is IMHO more natural and 6000K LEDs can simulate the old MV light atmosphere better than new 4000K MVs.

6000K LEDs can simulate the old MV light atmosphere better than new 4000K MVs.

But I would wait how the Chinese lamps look after some time...

By the way, in my recollections of MV lighting on the Czech side around 1985, when HPS had already ousted a lot of it, it was notoriously greenish.