Hello,

My parent's 175 watt mercury vapor yard light (power company owned) won't start. The lamp just glows a dim pink. I'm not too familiar with HID, is this what normally happens at EOL with mercury? The power company hasn't been out yet to fix it. I am just curious what would cause this.

-Nelson

It look like some fault - or ballast (loose connection) or lamp (main electrode weld), not normal wear.
Normally MV's go gradually dimmer and dimmer, so if you have nothing to compare, most people do not notice the brightness fall so severely (that is in my eyes the main reason for real MV inefficiency in real life).

It could possibly be a defective lamp. It sounds that the lamp is mercury starved. All phosphored mercury lamps starts with a more or less pink glow. That glow goes away as the pressure of the lamp rises. If there's not enough mercury, the pressure stays low.

To be more exact, a low pressure mercury discharge emits very little visible light, but a lot of UV light. The UV excites the phosphor, giving the pink glow, but because almost no visible light is generated (due to the abnormally low pressure), the spectrum isn't balanced by the blue light normally emitted by a higher pressure mercury discharge.


Hope this helps

TiCoune66: In MV arctube is huge amount of mercury and nothing it may react with (and e.g. oxidize as in fluorescent), so that would be only a consequence of severe arctube leak.

But i just remembered, then some MV's had one lead in wire thin to act as a fuse, to prevent violent explosion if the ballast fail short circuit and/or somebody accidentally put the lamp into incandescent fixture. If this fuse goes only to the top electrode (opposite end then is the starting probe), only the weak UV glow of the starting probe remain after powering up (it has not enough power to rise the arctube temperature, so pressure). And the totally black arctube may be the other consequence of the overcurrent, what caused the fuse to blow...

In both cases the fault is not recoverable...

Thanks for the replies everyone. If I find out what happened, I will let you know! I just looked at the lamp and it is now completely out.

-Nelson

The power company came out and replaced the lamp. It is working again, so the ballast either is fine or is starting to fail, but hasn't completely failed. We'll see how long the new lamp lasts.

Apparently, at first, the lamp would glow bright pink for a long time (maybe an hour or so?) and eventually light up, but at about half brightness. Over the next few days the lamp glowed a dimmer and dimmer pink until it didn't glow at all. Before this started, the lamp operated fine and was plenty bright.

-Nelson

It sounds as though one of the welds which carries current to the upper end of the arc tube came loose or failed.  Then the lamp remains in a state with a small discharge taking place between the lower main electrode and the adjacent starting probe.  If the lamp remains in glow like this the electrode materials will be sputtered away until the arc tube is so blackened that it emits no more light (which would explain the reduction of brightness you observed).  If left long enough in this state the electrode shank will be entirely sputtered away and the electrode tip will drop off.

That would make sense!