The other day, I noticed they fixed a dayburning NEMA head that's been running nonstop since May of 2012. The lamp was a bit green, indicating it was in use for maybe two years prior. In the time since it started dayburning it has only been turned off a handful of times, which were during power outages and they were off for only an hour. The lamp still looks to be the about same brightness it was in May 2012, and the color hasn't changed much either. Online I read that the start up of mercs is what shortens their lives the most.
Questions:
Each time the lamp starts, a little bit of sputter happens at the electrode ends. As the lamp ages, this sputter accumulates. Does the sputtering block uv out as time goes on, which causes the color to be green?
The average usable life of a merc is 24k useful hours. It has run for 3 years and 6 months. Would the average life depend on the amount of start ups or is it based on the lamp and how small the electrodes are in different lamps?
I also saw a BT bulb in a NEMA bucket that looks like it's been going since the late 80s, I'll place it when my Philips bulbs were made, which is 1987. Besides the fact that they had larger electrodes and the whitening emitter, how come they lasted way longer?

While most MV lamps are rated at 24k hours, that's really just a rough estimate. A good one can last a whole lot longer, and it really depends on how dim you're willing to let it get before it's no longer "useful". 24k hours is about 2 years and 9 months, and any decent MV will last much longer than that if it is continuously on. The life is based on both electrode size and frequency of starting. I think the reasons the old lamps lasted so long are exactly the reasons you mentioned: whitening emitter and large electrodes. The old lamps also usually did a better job of securing the arc tube, so it was less susceptible to physical damage.

I do not know exactly why MV lamps turn green as they age, but I'm sure it has to do with the emitter coating the inside of the arc tube.

I had a cheap HPS that actually lasted about 3 years of service until it started cycling and leaked.

I had a cheap HPS that actually lasted about 3 years of service until it started cycling and leaked.

we have a 35w HPS wallpack on the barn and the bulb in that only lasted a little under a year!  musta been a dud.  was a cheap cooper bulb that was included with the fixture.

Yeah those no name bulbs are typically no good.

Yes, the whitening matter allows for better lumen maintenance, so they can last longer without dimming out. Yeah, prolly the deposits cause the greening of the color appearance in clear lamps. Those 1980s Philips Lifeguard mercs are still plentiful here.

My Philips lifeguads have good color still, and start up pink. They've had some use since I see some whitening on the ends.

Oh, were you talking about clear or coated lamps?

Clear.

The anti blackening emissive coating leaves a greyish off white color on the arc tube wall, that is prolly what made the light turn slightly greenish. Blackening makes it even more green.

Quote from: Solanaceae on December 24, 2015, 06:32:30 PM

I had a cheap HPS that actually lasted about 3 years of service until it started cycling and leaked.

we have a 35w HPS wallpack on the barn and the bulb in that only lasted a little under a year!  musta been a dud.  was a cheap cooper bulb that was included with the fixture.

I have several church buildings I work on that use the 35W HPS bulbs.  I haven't had good luck with 35W HPS Philips bulbs, but seem to see the most luck with the Sylvania and GE 35W HPS.  Now all the ballasts are going out on them grrrrr.  I think.  I can screw in a CFL or incandescent bulb into the socket and it will light up, so until I figure out what I am going to do with the HPS, I'll just be using CFLs in the fixtures for now, they put out good light. 

@RyanF40T12: It sounds like the ignitors are failing. It should be a cheap fix since most are replaceable. Or you could just keep using CFLs.

It's a bit conflicting, what's worse, HPSyndrome or CFLunatic.

Get proper ignitors and make it work right as HPS

I think phosphor quality or rate of wear also has to do with the 'greening effect'. I have fired up many a coated MV for the first time (/DX or /C) and will be astoundingly bright red. Even at full run up, extra amount of warmer color, but after a few hundred hours....while still technically new, the lamps lose that extra bit of brilliance as the phosphors start to burn in from the heat and UV intensity.