Mercury Vapor lamp... how does it work? How do you know when it's bad? I'll try to shed some light on this topic. *Caution: material for the curious follows.
First, let's cover the basics: How it works.
A Mercury Vapor is a mix of electro-chemical and some mechanical ingenuity. Although some may not agree with me, I will state my case anyway. The lamp has a few basic parts. The reflector, which we all see, is used to direct the light in the intended direction... forward. Within the reflector, we have the actual bulb. The bulb contains the burner, mercury, and a fluorescent element. The width of the burner gap is critical for initial and sustained ignition of the lamp.
When your turn on your projection TV, a power supply devoted to the lamp (known as a ballast) passed about 300+ volts of high energy electricity through the lamp, but only for a few seconds. This energy arcs across the burner and vaporizes the Mercury. With the Mercury vaporized, the mercury is now free to move around within the bulb. The power supply then switches into a driving mode and begins feeding about 10,000+ volts at a lower energy. This allows the arcing between the burner gap to continue. The mercury, which is excited by all the electrical activity, begins to slam into the florescent element. In turn, the element glows brightly.
So, that's basically how it works... but what you don't see is the damage. At one time or another, we have all plugged something into the wall and POW... sparks fly. If you had looked close at the plug, you may have noticed some pitting or damage from the spark. This is an electrical arc. The same thing is happening inside your lamp, on a smaller scale. Each high energy ignition causes material to be worn away from the burner. The lost material builds up as contamination within the bulb and the loss of material causes the width of the burner gap to grow.
Some maybe wondering... "Is there a secret formula for extending my lamp's life?" The short answer is: "Stop watching it." The long answer is: Never leave your TV on when you are not watching it; Allow your lamp time to cool before turning it back on (5 minutes to be safe); Allow your lamp to reach it's optimal temperature before turning it off (20 minutes to be safe).
Now that we have that mess cleared up, on to the discovery section of this article: "How can I tell if my lamp is bad?"
Well, in most cases, there are warning signs: Picture is getting much darker; Seems fine at first, but then goes out and comes back on in a moment; Turns off after a period of time or doesn't light at all; I heard a loud pop. All of these are classic warnings or indicators that your lamp may need some attention.
You should allow your TV is cool for about 20 minutes and pull out wall plug
and then remove the lamp for inspection. You will need a well lit area to get a good look at it. Do a once over: Did the bulb burst; Does it look smoked up? If it looks good, have a glance at the base of the burner:
Does it have a smokey mark on one side? This is the contamination from the burner gap. This contamination builds up throughout the life cycle of the lamp. As the burner gap grows, the lamp resists the electricity that is be pushed to it to make it burn. This resistance creates heat. Some lamps will create so much heat that the glass surrounding the burner will begin to melt and swell. You may look into your lamp and see a big silvery blob protruding from this area. These are all clear indicators of trouble in the works.
Unfortunately, some lamp show no visual signs at all... for these, you can only replace them and hold your breathe.
I hope you are able to use this information to better guide your lamp purchasing decisions. Let me know it this was helpful.