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Why the burn-in worries w/ RPTV?


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#1 of 10 DaveF

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Posted May 23 2001 - 08:26 AM

Pardon my ignorance, but I've been wondering why burn-in is such a concern with RPTVs, when it's not an issue with direct-view TVs (and computer monitors, etc). Could someone explain this, or point me to an explanation? Thanks.

#2 of 10 Kevin P

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Posted May 23 2001 - 08:47 AM

The short story is that projection systems (RPTV, FPTV) use three relatively small CRTs (usually 7" but sometimes 8 or 9") to project an image onto a much larger screen (40-80" for RPTV, even bigger for FP). In order to produce a bright enough image, the phosphors have to be driven harder (produce MUCH more light) per square inch than a direct view CRT does. This accelerates the normal aging process of the phosphors and the risk of burn in.

Direct view CRTs aren't immune to burn-in either--though you don't often see it on a direct view television due to the wide variety of images shown, just look at an older ATM, flight arrival/departure monitors at the airport or an older monochrome "dumb" terminal and chances are you'll see burn-in on those, due to the static images that are often displayed on these for extended periods of time.

Newer CRTs are more robust than older ones but burn-in can and does happen, especially if static images are displayed for extended periods of time at high contrast levels.

KJP


#3 of 10 RyanDinan

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Posted May 23 2001 - 08:52 AM

Dave,

Most Direct-view and computer monitors don't have to have their contrast levels up so high, because one looks directly at the CRT, hence, direct-view. RPTV's however have to reflect their light off a mirror onto a screen many times the CRT's physical size, so they must put out more light to get a decent picture. This is where phosphor burn can happen. Even though the picture may look as bright as a direct-view set, the CRT is being driven way to hard - Much more than a direct view would have to do to get the same brightness.

-Ryan Dinan

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#4 of 10 DaveF

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Posted May 23 2001 - 10:23 AM

Thanks for the replies and answers. My guess was that it was the small CRT / high intensity. But since direct-view CRTs are so much more robust than from a decade ago, I wasn't sure.

Well, mystery solved. Thanks again.

#5 of 10 SteveMc

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Posted May 23 2001 - 06:06 PM

quote:
just look at an older ATM, flight arrival/departure monitors at the airport or an older monochrome "dumb" terminal and chances are you'll see burn-in on those, due to the static images that are often displayed on these for extended periods of time[/quote]

Exactly. This is precisely why there are "screen savers" for your PC. If you were to leave the monitor on at your desk when you went home for the night, eventually you'd see slight burn in an uneven wear. Not as much of a problem now as it was 10 years ago, now screen savers are more for show...especially when you've got scrolling Britney pics Posted Image

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#6 of 10 errol

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Posted May 23 2001 - 10:49 PM

Hi,

I've seen it on a number of display sets at a couple of dealers. Very disturbing. Even more disturbing is that it is very much avoidable if the sets don't come torch mode as the default setting.

Thanks,
Errol

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#7 of 10 DaveF

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Posted May 24 2001 - 07:12 AM

[quote]Exactly. This is precisely why there are "screen savers" for your PC. If you were to leave the monitor on at your desk when you went home for the night, eventually you'd see slight burn in an uneven wear.[/QUOTE}

I've only seen burn-in on machines like ATMs, where they run 24/7 with the same static image for the majority of that time. I haven't seen burn-in on a TV or computer monitor in the past decade, maybe. My understanding is that screen savers were no longer necessary at least five years ago (because of both higher quality monitors and auto shut-off features). Likewise, most TVs (in my experience) are only on a few hours a day, much less 24/7 with static images.

I guess I'd be surprised if burn-in was a problem even on floor model direct views (assuming running demo material). But I can see how the RPTVs might suffer problems more quickly.

So, has anyone seen burn-in on direct views? Is that problem pretty much extinct given normal usage?

#8 of 10 TerryBlauser

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Posted May 24 2001 - 10:17 AM

I wouldn't call it normal usage but my wife burned in the screen arrangement from one of the shopping channels that she watched (and patronized into the wee hours) you know item number, price, minutes remaining,etc, etc. Even turned off you could read the fixed label contents. At the office we managed to "burn in" a $12000 plasma monitor by leaving the PC desktop running 24/7. ANY monitor which has an intensity adjustment is capable of having the output of pixels change over time and with varied activity levels. Constantly black areas are resting while varied content areas are at half active output and bright areas are working hard. Constant dials on video games, logos, black bars, etc. cause different aging in different areas and you will eventually be able to discern a difference. IMHO. Best advice keep the content and format varied.



#9 of 10 RyanDinan

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Posted May 25 2001 - 03:01 AM

- And to keep you picture level (contrast) turned down. For most RPTV's this is in the 30-40% range.

-Ryan Dinan

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#10 of 10 Ryan Wright

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Posted May 25 2001 - 11:47 AM

quote:


eventually you'd see slight burn in an uneven wear.


Make that VERY eventually. It is difficult to burn in a VGA monitor nowadays. I've seen it once. This was on a PC that was left on with the NT login box displayed roughly 22 hours out of the day at high brightness levels. After about a year of this, I could see a very slight ghost of the NT login box with the monitor turned off. It wasn't visible while using it for other tasks.

RPTVs are different though and will burn it easily if you aren't careful. I have the brightness/contrast set below 40% on my TW65X81. It's still PLENTY bright, even during the daytime.


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