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01/11/2005 06:21:30 PM · #1 |
That has been a fair bit of talk about CRT monitors that are getting out of calibration, at one time I designed the CRTs that went into monitors and so know a bit about what happens to them as they age.
The main effect from aging will be the cathode wearing out, it has a limited number of electrons that it can emit. The part of the cathode that is run the hardest is right in the center, this is also the area of the cathode that puts out the beam for very dim part of a photos (low beam current = dark part of image).
The effect of this is that when the cathode ages the center goes bad and the low level parts of the photo are lost. Some monitors have a black level control to help adjust for this, some display cards have a similar control. But if you have neither then your going to be missing the black part of your photos.
The other effect that you will notice is that the screen will not be as crisp as it was when the monitor was new, you have to use a large area of the cathode and there for the electron beam is also larger. Your gamma will also start to change as this happens.
In the end what you really want to do is slow down the aging of your CRT, there are two things you can do to help, one donĂ¢€™t run the monitor at full brightness and two donĂ¢€™t use a screen saver that puts up an images that has any degree of brightness. The best would be to simply blank the screen if the computer has not been used for more then 10 minutes or so. I see computers left on with all sorts of fancy screen savers running that are using up the lift of the CRT for not good reason. If you must have a screen saver that puts on some kind of show use one where the screen is mostly black with just a few lines, you will get a lot more life out of your monitor if you do.
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01/11/2005 06:26:17 PM · #2 |
| I use to let my monitor go black after 20 minutes of no use. I now have an LCD so this is now less of a problem. |
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01/11/2005 08:07:12 PM · #3 |
Originally posted by drz01:
I use to let my monitor go black after 20 minutes of no use. I now have an LCD so this is now less of a problem. |
Yes and no...
Your LCD monitor has a backlight that is essentially a fluorescent tube. These tubes lose brightness with age. the more they are on, the faster they will age.
edit:
Scott, thanks for the very informative overview of why we see the aging effects that we do on CRTs. Funny i was just looking at my old CRT at work, comparing it to the screen on my brand new IBM Thinkpad T42, and thinking... this CRT is toast! It's darker than an f/5.6 zoom and about as sharp as a pinhole camera image.
Message edited by author 2005-01-11 20:10:49.
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01/11/2005 08:12:21 PM · #4 |
ive noticed a small black dot (looks like a lost pixel) towards to bottom center of my screen. is normal?..or a sign of things to come?
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01/11/2005 08:24:00 PM · #5 |
Originally posted by maxj:
ive noticed a small black dot (looks like a lost pixel) towards to bottom center of my screen. is normal?..or a sign of things to come? |
I donĂ¢€™t know of an aging mechanism that would make a black dot off center. We use to get an occasional black dot when a small piece of something would end up on the screen. If you get a black dot in the center of the screen it is most likely ion damage, but almost all CRT have what are called ion traps to try and avoid this. |
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01/11/2005 08:41:47 PM · #6 |
I wasn't aware how badly they age, as it happens gradually you get used to it.
Recently realised one of my monitors was way off the mark, and could not be calibrated back to "normal".
Replaced one of the (had x2 17") yesterday and can't believe how bad the other one had got when I compare it to the new one.
Good tips there Scott.
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01/11/2005 10:55:29 PM · #7 |
Originally posted by kirbic:
Originally posted by drz01:
I use to let my monitor go black after 20 minutes of no use. I now have an LCD so this is now less of a problem. |
Yes and no...
Your LCD monitor has a backlight that is essentially a fluorescent tube. These tubes lose brightness with age. the more they are on, the faster they will age. |
I thought those LCDs were rated for something like 1400 (14 thousand?) hours of use ... one of the reasons laptops are so expensive. |
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01/11/2005 11:03:26 PM · #8 |
Originally posted by GeneralE:
Originally posted by kirbic:
Originally posted by drz01:
I use to let my monitor go black after 20 minutes of no use. I now have an LCD so this is now less of a problem. |
Yes and no...
Your LCD monitor has a backlight that is essentially a fluorescent tube. These tubes lose brightness with age. the more they are on, the faster they will age. |
I thought those LCDs were rated for something like 1400 (14 thousand?) hours of use ... one of the reasons laptops are so expensive. |
Yup, they do have long lives, but remember that if someone uses a "screen killer" that keeps the monitor on all the time, it's getting over 8,000 hours of use per year if the system is left on. Screen life is rated pretty liberally as well, and at the end of the design lifetime you can bet there is significant change in the backlight brightness.
More and more, I see folks just leaving their systems on 24/7, and ignoring the energy costs, this actually makes some sense, since the components don't go through as many thermal cycles. Thermal cycling is what kills electronics, as a matter of fact it is how we conduct accelerated reliability tests.
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