Conflicting CCFL/Backlight Life span Opinions

[dsvochak]

Apparently, there are conflicting opinions regarding whether turning the monitor on and off has any impact on the life span of the backlight/ccfl.

This morning, in this thread http://forum.thinkpads.com/viewtopic.php?t=27503 I read this:

christopher_wolf wrote:

You could also try dimming the screen and shutting it off frequently when not in use....but that shortens the CCFL backlights' life as well.

Which is the opposite of the advice in this thread: http://forum.thinkpads.com/viewtopic.php?t=14134

And then there is this recent thread: http://forum.thinkpads.com/viewtopic.php?t=27509

No one offering an opinion has cited a source. If anyone has a link to a reliable source I'd appreciate it. If I had to vote, I'd say regularly turning off the monitor has no effect on backlight/ccfl life span because it hasn't for any of my machines.

[christopher_wolf]

Frequently changing the brightness from one extreme to the other probably has an effect simply because of the hardware; the more operational cycles it undergoes, the slightly higher the chance that its MTBF is going to be reduced by a tiny amount. It isn't a large amount either. Then again, consider the operation of CCFLs; the two biggest points that have been focused on have been dimming ratio range and lifetime in conjunction. The main thing that affects the lifespan of any given CCFL device is the current provided to the CCFL at a certain voltage. If it is at the minimum in manufacturer specs, as most controllers pin it at, you should, theoretically, get maximum lifetime and minimal wear out of it.

Now, the problem with that is that it, with a linear controller, it would sacrifice CCFL lifespan and dimming range to give you good efficiency and would, frequently, go past the current tolerances provided by th CCFL manufacturer. PWM controllers provided wider dimming ranges but at the cost of non-optimal waveforms, also degrading the CCFL lifespan somewhat. Newer controllers, on the other hand, offer the best of both, called multimode, and adjuest accordingly depending on what is input by the user. Everytime an adjustment has to be made, there is a slight error that has to be taken care of via a series of control functions. Now, the goal is to minimize the error until a steady-state waveform is reached; the error produces both undesired output, which the control system uses to correct it, and non-optimal operating conditions for the CCFL. Hence, continued adjustment of the operating voltages and current will generate a frequent need to adjust the CCFL and, unavoidably, a tiny error will always be produced where the state of the CCFL is non-optimal for either efficiency or lifespan considerations.

Linear-tech ( http://www.linear.com/index.jsp ) has some good articles on this; I found one because it was the closest I could grab right now (kind busy);

See; http://tinyurl.com/l9jfp

HTH

See

[dsvochak]

Unless "Frequently changing the brightness from one extreme to the other..." is the same as using F3 to turn off the monitor, neither the response nor the link directly address the issue.

Both essentially make the point that "The main thing that affects the life span of any given CCFL device is the current provided to the CCFL at a certain voltage." The article cited indicates that "PWM control schemes offer wide dimming range but produce wave forms that may degrade CCFL life, and waste power at higher CCFL currents." (pg 10). The article further states "To achieve maximum life CCFL drive should be sinusoidal, contain zero DC component, and not exceed the CCFL manufacturers minimum and maximum operating current ratings." (pg. 9).

To paraphrase, apparently exceeding minimum and maximum operating current ratings and/or using control schemes producing certain wave forms, may degrade CCFL life. Which appears to be significantly different than "... dimming the screen and shutting it off frequently when not in use...shortens the CCFL backlights' life."

Is there any evidence that notebooks in general, and Thinkpads in particular, exceed minimum and maximum operating current ratings and/or use control schemes producing the wave forms which may degrade CCFL life?

[christopher_wolf]

Is there any evidence that notebooks in general, and Thinkpads in particular, exceed minimum and maximum operating current ratings and/or use control schemes producing the wave forms which may degrade CCFL life?

Give me the CCFL specs for Thinkpads then. Quiz time though; there is one control setup in there that *does* goes above and below the ranges specified by the CCFL manufacturer for operation. That is the linear control scheme. So, and the older Thinkpads and laptops might have this, changing the settings if you had that control scheme would run the CCFL at non-standard currents. The others control their usage pretty well although there will always be a tiny error that is going to be constantly accounted for, be it a DC component or simple over-shoot. I don't actually know what brand and chip the Thinkpads use for a controller/regulator in this regard. It would help to know that as well.