Do the Bulbs Dim?

They do dim but retain most of their brightness. When someone puts in a new bulb they usually can see the difference in brightness.

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How long till dimming?

Most of the dimming occurs within the first few hundred hours of use.

The MTBF (mean time before failure) rating for the lamp for my set is 6,000 - 8,000 hours. I checked my hours in the service menu and decided to replace it with a new lamp at about 6,500 hours. The old lamp is stored as a "just in case" for when the "new" lamp goes. It will afford me a down time of no more than the 15 minutes to change out the lamp that should last more than long enough to get a replacement lamp.


There is no definitive lifetime for these lamps, only averages. The only thing you can do is not abuse them with quick, frequent power cycles. If you properly calibrate your set, you should be able to judge whether you need to re-calibrate after several months. Don't worry, just sit back and enjoy the show.


YMMV

the best part of the "dimming" bulb is that after the bulb dims your set is still 3x brighter than any plasma. In other words i wouldnt worry about it.

And, the worst part is.... grayscale/color shift due to the fact that the lamp does not dim "uniformly".


Hammer

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I guess that's where the recommendation to wait till a set has a few hundred hours on it before an ISF calibration.

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That's the first I've heard about that. Is this from your own personal experience, or is something that is documented?

How much does it cost to Calibrate a TV?

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I'm curious to hear more about this. Are you saying that grayscale temps vary as lamp dims AND that the grayscale temps don't change evenly across IRE range as this happens?

What I've been told is the higher freqency color(s) burn off faster. When it comes to the visible light output of a lamp, the Violet/Blue burns out of the lamp faster than Green/Yellow/Red, in that order. So when the blues start to burn out of the lamp, the picture can begin to take a yellow/green hue. This is also partly due to the fact that, for our eyes to see gray properly, more Blue output is required in the first place.


Someone with a masters in light theory will probably correct me, but that's what I've been told.


Hammer

I had previously thought that intensity was the only change over time as the lamp dimmed. I'll have to keep an eye on my grayscale and see if some of this behavior is observable over the lifespan of the bulb.

Interesting reading. What is considered quick power up cycles?

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I don't have a masters but. Lamps are manufactured to burn at one color, measured in degrees Kelvin, and generally do not change color during their life.

Bulbs do shift with age. The only way I can see for the tv designers to control this is to limit the life of the bulb to the "sweet spot", either by limiting the hours of use by counting or possibly monitoring the current drawn over the "useful life" of the bulb and shutting it down. This does not preclude the bulbs popping by themselves.


Sanjay Joshi knows his stuff. He's more interested in aquariums than tv's, but the physics is the same. Send him a note (or a bulb/ballast to test).

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"shift" ? Do not confuse lumen output with colour temp. Again, lamps generally can not change colour!!

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By the way, there is not one thing said above which is true.

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I've had two pop while just sitting there watching tv. I never noticed any dimming ... but I DO notice when the new one goes in, it's brighter. Still, without running test patterns periodically, the dimming is unnoticeable. There was no fast deterioration prior to the bulbs blowing. Just ... "bink."

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Well I have a PHD in physics and different colors don't burn off any quicker than the others. The light emitted is a combination of all the colors. There's no real magic to it.