up until today i was pondering what causes mercury vapor lamps to have the highest rate of lumen deprecation of all hid lamps ,the awnser blackining of the arctube,if i recall correctly they used to sell mercury vapor lamps  that preventd blackening,i think they they should reuse this idea,and others for example i thought why not use ceramic arc tubes for mercury vapor lamps? the ceramic can opperate at higher tempatures and pressures raising efficency,so the goverment should have  thought of ways to improve mercury vapors lamps instead of declaring them obsolete if you ask me they should ban high pressure sodium and light the roads the right way,with mercury vapor.

The lumen depreciation is bad mostly because they lasted so long! The older ones would keep burning well after their "rated" life of 24,000 hrs and refused to die. The ones without the Bonus Line/Lifeguard-style electrodes (i.e., the lamps that blackened rather than whitened first) would be even quicker to depreciate. Part of the problem is the phosphor (on coated lamps): An electrodeless induction light, long-life fluorescent, white LED, etc will also suffer quite a bit of lumen depreciation over 20K-100K hours!

Actually, I believe metal halide lumen depreciation is worse, over their shorter life. The short arc tubes often go completely black, within a few years. I don't know if a ceramic arc tube would make a difference in a mercury vapor lamp. It's an interesting concept though (would be like a non-cycling HPS at its end-of-life).

The lumen depreciation is bad mostly because they lasted so long! The older ones would keep burning well after their "rated" life of 24,000 hrs and refused to die. The ones without the Bonus Line/Lifeguard-style electrodes (i.e., the lamps that blackened rather than whitened first) would be even quicker to depreciate. Part of the problem is the phosphor (on coated lamps): An electrodeless induction light, long-life fluorescent, white LED, etc will also suffer quite a bit of lumen depreciation over 20K-100K hours!

Actually, I believe metal halide lumen depreciation is worse, over their shorter life. The short arc tubes often go completely black, within a few years. I don't know if a ceramic arc tube would make a difference in a mercury vapor lamp. It's an interesting concept though (would be like a non-cycling HPS at its end-of-life).

Remember Alain, a mercury arc will cause the PCA to fall apart!

well i still think they should have tried to improve mercury vapor lamps before declaring them obsolete,ceramic arctubes would be an intresting alternative to quartz,because there is no room for an auxliary electrode a ceramic mercury vapor lamp would have to be pulse started.they should also use clear lamps although the lacking red sprectrum gives them a poor color rendering index of around 17 they distribute loght better in semi-cutoff fixtures such as clamshells,and cobraheads.

I agree with Alain. Metal halide generally have the worst lumen depreciation...many times mercury lamps are left burning beyond their rated life, therefore, they eventually will dim to extreme levels. However, I've noticed that certain brands of MV have dimmed (blackened arc-tubes) more than others. In the US made lamps, GE, Norelco, and later, Philips all use smaller electrodes than Sylvania and Westinghouse (don't know much about Duro-Test or some of the other brands), and those lamps seemed to be more prone to blackening.

The worse lamps I've seen were the US made Philips in the mid 90's to early 2000's. They had dropped the original Westinghouse designed electrodes in favor of a smaller version, which, IMO, was a disaster. I've seen some of those lamps dim to extreme levels after only a couple years. Ironically, I have a newer Chinese made 175w installed in a NEMA head at work that has been burning for a 1 1/2 years and still looks relatively new.

One last thing to consider are the phosphor coated lamps. All phosphors will degrade after awhile and instead of converting UV into additional red light, they merely diffuse the visible light from the arc-tube and maybe even block some of it as well.

the reason smaller electrodes cause blackining is because the smaller diamater of these electrodes make the electrode run hotter causing more sputtering and evaporation which in turn makes the lamp arctube black,for lamps to preform their best critical components have to be taken into account for example a lamp with larger electrodes runs the electrodes at a cooler tempature resulting in less evaporation of the tungsten,therefore reducing blackening and in turn larger electrodes reduce lumen depreciation ,contaminants also can affect lamp preformance which is why the arctubes have to go through an extensive cleaning process prior to lamp manufacturing,higher pressure also causes an increse in efficency as the higher tempature causes more of the mercury to be vaporized in the arc stream,which is why i brought up ceramic arc tubes,think if ceramic arctubes improved metal halide lamps,then surely theres room for improvement in mercury vapor lamps.

CERAMIC ARCTUBE-ABILITY TO OPERATE UNDER HIGHER TEMPATURES AND PRESSURES THAN QUARTZ
EQUALS
HIGHER VAPOR TEMPATURE
HIGHER VAPOR PRESSURE
MORE LIGHT
LESS BLACKINING
LESS LUMEN DEPRECIATION

of course i would assume that with limited space avalible in the slinder ceramic arctube it would have to be pulse started,also with these suggested improvements it may be possibe to create a 250 watt mercury vapor that produces equal amounts as a 250 watt high pressure sodium.although i doubt that ceramic mercury vapor lamps will catch on even though they would be cheaper than ceramic metal halide lamps.

Part of the reason that most MV lamps are rated to last 24,000 hours is because of the lumen depreciation and efficiency.  As we all well know, a good MV lamp can easily keep burning for well over double it's rated life.  At 50,000+ hours, they have a pleasant soft glow, but still draw their full current.

They do make some special extra high pressure mercury vapor lamps, that basicly work like a metal halide without the halides.  I believe they are used as projection lamps for projection TVs and video projectors.

@mr.big how can a mercury arc cause the pca to fall apart.

the reason smaller electrodes cause blackining is because the smaller diamater of these electrodes make the electrode run hotter causing more sputtering and evaporation which in turn makes the lamp arctube black,for lamps to preform their best critical components have to be taken into account for example a lamp with larger electrodes runs the electrodes at a cooler tempature resulting in less evaporation of the tungsten,therefore reducing blackening and in turn larger electrodes reduce lumen depreciation ,contaminants also can affect lamp preformance which is why the arctubes have to go through an extensive cleaning process prior to lamp manufacturing,higher pressure also causes an increse in efficency as the higher tempature causes more of the mercury to be vaporized in the arc stream,which is why i brought up ceramic arc tubes,think if ceramic arctubes improved metal halide lamps,then surely theres room for improvement in mercury vapor lamps.

CERAMIC ARCTUBE-ABILITY TO OPERATE UNDER HIGHER TEMPATURES AND PRESSURES THAN QUARTZ
EQUALS
HIGHER VAPOR TEMPATURE
HIGHER VAPOR PRESSURE
MORE LIGHT
LESS BLACKINING
LESS LUMEN DEPRECIATION

of course i would assume that with limited space avalible in the slinder ceramic arctube it would have to be pulse started,also with these suggested improvements it may be possibe to create a 250 watt mercury vapor that produces equal amounts as a 250 watt high pressure sodium.although i doubt that ceramic mercury vapor lamps will catch on even though they would be cheaper than ceramic metal halide lamps.

250W MV is nearly at maximum MV efficacy, regardless of pressure. The UHP in projectors is used only, because it gives more condensed light source for the optic, still keeping the cost and efficacy reasonable - compare to xenons.

Last week I got a lantern freshly removed from lighting a street, having done around 40 years in service. It was fitted with an 80w mercury lamp. It is quite common for street lighting crews to write the month and year of installation on the lamp cap with a permanent marker pen, and to my surprise the lamp was installed in February 1991. Hence, the lamp had done just over 18 years of full nightly service. I powered it up at home, and it was very dim, with the light output no greater than what you would get from a 25w incandescent lamp, and the arc was a little unstable at full brightness too.

Last week I got a lantern freshly removed from lighting a street, having done around 40 years in service. It was fitted with an 80w mercury lamp. It is quite common for street lighting crews to write the month and year of installation on the lamp cap with a permanent marker pen, and to my surprise the lamp was installed in February 1991. Hence, the lamp had done just over 18 years of full nightly service. I powered it up at home, and it was very dim, with the light output no greater than what you would get from a 25w incandescent lamp, and the arc was a little unstable at full brightness too.

I have some Westy lamps (I MEAN LAMPS NOT LANTERNS) have had 40 years of service....they were labelled from 1969! I got the lamps around 2007-2008 so basically 38-39 years! Those lamps are the longest in service that ever had in my collection...they are /W and /C coated lamps 175 watt.....175 watt will last forever while other wattages dont last as long...the 2nd longest are 100 watt and my longest serviced 100 watt is a Sylvania 100 watt MV /DX color lighting the streets from 1973 to 2006...the Sylvania 100 watt is dimmer than the 175 watt Westy.....Westies ive noticed will last and stay bright for about roughly 20 years or so before starting to get dimmer!

In my country last year changed all the last mercury lanterns. began to change in 1984 but only changed only if a call to report to fixed.

in san jose the capital, a couple of years ago I remember one lantern in front a house of my best friend, was 400w mercury but the light was extremely green, he told me that the last time the repaired was in 1979   but illuminated less a 175w...