Adapting preventative measures for a move from CRT to LCD

[Mxsmanic]

After using CRTs for years, I more or less began to understand how to
treat them to lengthen their lives and improve performance. I figured
out that:

- Leaving a CRT on when it is not in use is bad.

- Leaving fixed images on the screen for very long periods is bad.

- A dark screen preserves the CRT longer than a bright screen (most
screen savers seem to be designed around this premise).

- Switching the CRT to power-saving mode probably is best for long life
(eliminates the thermal shock of a complete power-off/power-on cycle,
but reduces wear and tear on the cathode when the CRT is not in use).

- CRTs don't like magnetic fields, and should be occasionally cycled off
completely and turned back on to degauss the screen (if there is no
degauss button).

- For extremely critical work, CRTs have to be calibrated after they
warm up for an hour or so.

- CRTs don't like anything sitting on top of the tube (I'm surprised how
many people stack magazines or papers on top of their CRTs).

- CRTs like low resolutions and low scan frequencies better than high
resolutions and high scan frequencies (I think?).

Now ... the question that arises is how to modify all this for an LCD
flat-panel screen:

1. How long a duty cycle should a LCD have? How long should it be left
on, unused, before it's best to turn it off? I'm thinking here mainly
of the backlight, which I assume is the major wearing component over
time. If it's just a fluorescent lamp, it probably likes long duty
cycles and suffers most when first turned on.

2. Do fixed images on the screen do any damage over time?

3. Is a mostly-dark screensaver really a good idea? I mean, the
backlight is always on, so a dark screen really is just absorbing the
backlight and heating the screen. Would it make more sense to use a
screensaver with a mostly-white screen? Or is a screensaver really
worth bothering with at all? What about a blank white screen (minimal
heat and equal settings for all pixels)? What puts the most stress on
individual pixels?

4. Is there a difference between power-saving mode and being completely
off for a flat panel? If so, which is preferable for long life?

5. Do LCDs shift significantly in performance over time? In what ways?

6. I presume that LCDs don't care about scan frequencies or resolutions,
since nothing is really being scanned, anyway. True? I imagine that
just running the screen at its native resolution all the time is best,
if there's any difference at all (?).

What does the brightness control adjust on an LCD? Does it actually do
something to the backlight or does it just control how the pixels are
driven? Does lower brightness extend life?

 

[Bob Niland]

- Leaving a CRT on when it is not in use is bad.

That depends. Frequent power-cycling can be more stressful.
I used to leave mine on unless I was not going to use it
for at least 2 hours.

- Leaving fixed images on the screen for very long periods is bad.

Definitely.
Changing your wallpaper from time to time is wise.

- A dark screen preserves the CRT longer than a bright screen

"darker", but not "black". Using a screensaver of video
black level can "poison the cathode". I used Windows
Starfield - minimal signal, burned in all screen locations
about equally.

- Switching the CRT to power-saving mode probably is best
for long life ...

I'll let others opine here. I never really trusted it.

Now ... the question that arises is how to modify all
this for an LCD flat-panel screen:

Indeed. The answers may be interesting.

 

[Mxsmanic]

That depends. Frequent power-cycling can be more stressful.
I used to leave mine on unless I was not going to use it
for at least 2 hours.

At work I left CRTs on all day, then usually turned them off at night.

At home I originally turned the CRT off at night, or when I left the
house for any period of more than 90 minutes or so. Later, as the CRT
aged, I let it switch to power-saver mode instead, figuring that it
would last longer if the filament stayed warm and shocks were avoided.

Overall, it irritated me that the CRT was really just a big,
old-fashioned vacuum tube. Flat panels have been around for forty years
and they _still_ aren't up to match CRTs. How long will it take?

Definitely.
Changing your wallpaper from time to time is wise.

I used screensavers and changed wallpaper regularly. I never actually
saw a burned-in color monitor outside of ATMs and things like displays
at airports, but I didn't want to take any risks.

"darker", but not "black". Using a screensaver of video
black level can "poison the cathode".

Hmm ... that's interesting! How does the "poisoning" happen?

I never used completely black screensavers, mainly because it was too
hard to see if the CRT was on or not.

I'll let others opine here. I never really trusted it.

I wonder if anyone has ever done controlled tests. On the one hand, you
avoid the shock of heating a cold tube suddenly. But at the same time,
there must be some wear and tear if the filament is warm (but how warm
is it it kept?).

Indeed. The answers may be interesting.

If anyone has done any experimenting yet.

 

[Bob Niland]

Hmm ... that's interesting! How does the "poisoning" happen?

Although Bob Myers just wrote on this lately, here's
one of his full explanations from some years ago:
<http://groups-beta.google.com/group/rec.audio.tech/msg/862313fa13419a99>

 

[Bob Myers]

1. How long a duty cycle should a LCD have? How long should it be left
on, unused, before it's best to turn it off? I'm thinking here mainly
of the backlight, which I assume is the major wearing component over
time. If it's just a fluorescent lamp, it probably likes long duty
cycles and suffers most when first turned on.

The simplest answer here is to treat it just like a CRT.
The wearout mechanisms for the backlight tubes, and their
lifetimes, are comparable to CRTs, and so is the tradeoff between
the usual aging and the turn-on/off transients in terms of their
effects on overall reliability. Someone might be able to
come up with a slightly modified schedule by looking at the
specifics of LCDs vs. CRTs, but I seriously doubt it would
be worth the effort.

2. Do fixed images on the screen do any damage over time?

It is still POSSIBLE with the LCD to see a phenomenon known
as "image sticking," which is analogous to burn-in although due to
completely different phenomena. It is not nearly as likely with
current LCDs, but there's still little reason to be leaving a static
image on the screen for long periods.

3. Is a mostly-dark screensaver really a good idea? I mean, the
backlight is always on, so a dark screen really is just absorbing the
backlight and heating the screen. Would it make more sense to use a
screensaver with a mostly-white screen? Or is a screensaver really
worth bothering with at all? What about a blank white screen (minimal
heat and equal settings for all pixels)? What puts the most stress on
individual pixels?

Screensavers do absolutely no good for an LCD, for the reason you
mentioned - the backlight is still always on full blast and consuming
power, no matter what. The LC material itself does not care if it's in
the "black" or "white" state, so the decision would basically be if you
want to be using the monitor as a night-light... Seriously, the best
thing you can do for it is to simply shut the thing down when it's not
in use for extended periods, just like a CRT.

4. Is there a difference between power-saving mode and being completely
off for a flat panel? If so, which is preferable for long life?

Assuming that in the power-save mode, the backlight is shut off,
there would be no difference. Being "completely shut off" would
save a bit on the rest of the monitor, i.e., the power supply,
interface components, etc., and so is preferable. However, in most
LCD monitors I'm familiar with, there is only one "power-save"
state anyway, and it essentially IS the same as "completely shut off"
- the only thing up and running is just enough circuitry to detect
active video starting up again, in order to bring the monitor OUT
of the power-save state. The backlight and inverter, and the interface
electronics (for the most part) would be completely shut down.

5. Do LCDs shift significantly in performance over time? In what ways?

The LCD itself, no; there is with time the possibility of such things
as drivers failing, or even getting more stuck on/off pixels within the
panel, with age, but the basic visual performance does not change.
The exception to this is, again, the backlight, which will slowly lose
brightness with time and in that process possibly experience some
color shift (which could be compensated for, to some degree, via
the monitor's white balance controls if such are provided). For
the most part, though, everything stays LOOKING the same right
up to the point where it fails for good.

6. I presume that LCDs don't care about scan frequencies or resolutions,
since nothing is really being scanned, anyway. True?

Yes and no. The LCD panel itself is generally operated at a
fixed rate, or within a relatively small range of timings. The fact
that you can throw different video timings at the monitor has to
do with the scaling and frame-rate conversion capabilities of
digital ICs in the "front end" (the interface circuits), and again these
will either work or they won't - they will not slowly degrade with
time, in any way that affects the visible performance. One
possible exception would be drift in some of the front-end
components having to do with the stability of the sampling clocks
(generated by phase-locked loop circuits, somewhat as in a CRT
deflection circuit), so it is possible that the stability of the image
might slowly become poorer as, say, a capacitor or some such
external component aged. But it's not nearly as likely as in a
CRT; again, the general rule will be that things will work just fine
right up to the point where they fail completely, as is the case with
most digital equipment.

I imagine that
just running the screen at its native resolution all the time is best,
if there's any difference at all (?).

No real difference in terms of reliability; the performance of the
product in terms of the delivered image is generally, of course,
best at the "native resolution."

What does the brightness control adjust on an LCD? Does it actually do
something to the backlight or does it just control how the pixels are
driven? Does lower brightness extend life?

Most often, this is controlling the backlight level; there may be
additional controls (perhaps labelled "contrast") which would
play around with the gray-scale range, i.e., how the panel is
actually being driven. Lower backlight brightness would extend
life somewhat; the latter sort of control would have essentially zero
impact on lifetime.

Bob M.

 

[Bob Myers]

Overall, it irritated me that the CRT was really just a big,
old-fashioned vacuum tube. Flat panels have been around for forty years
and they _still_ aren't up to match CRTs. How long will it take?

Well, no one ever said that things had to be "better" just because
they were newer. I seem to recall that this thing they call the
"wheel" has been around for some time without significant
fundamental improvement....

Flat panels in the sense of the modern color TFT-LCD have really
been in volume production for only about 15 years or so; there
have been LCDs of other types for longer than that, but please keep
in mind that the first things you might realistically call an LC display
(back in the 1960s) were pretty much laboratory curiousities, at
about the same level of development as the really early CRTs.
(And does anyone want to take a guess at how old the CRT is?)

For that matter, "flat panel" covers a very wide range of technologies,
including some that aren't all THAT different from the CRT itself
(color plasma, for example, or better yet the color FED - which
STILL has not made any significant inroads in the commercial
display markets).

Hang in there, though - better days ARE coming.

Bob M.

 

[Mxsmanic]

Hang in there, though - better days ARE coming.

I hope so. My eyes have suffered through a lot of crummy monitors, even
though I try to buy the best I can afford. There's no such thing as a
monitor that's _too_ good.

 

[Mxsmanic]

The simplest answer here is to treat it just like a CRT.
The wearout mechanisms for the backlight tubes, and their
lifetimes, are comparable to CRTs, and so is the tradeoff between
the usual aging and the turn-on/off transients in terms of their
effects on overall reliability. Someone might be able to
come up with a slightly modified schedule by looking at the
specifics of LCDs vs. CRTs, but I seriously doubt it would
be worth the effort.

Do the backlights have heated filaments, or are they cold cathode types,
or what? As I recall, fluorescent lamps without heated filaments last
longer.

It is still POSSIBLE with the LCD to see a phenomenon known
as "image sticking," which is analogous to burn-in although due to
completely different phenomena. It is not nearly as likely with
current LCDs, but there's still little reason to be leaving a static
image on the screen for long periods.

I worry mostly about some of the static elements of standard windows on
the screen; the buttons are always in the same place on full-screen
windows, and so on.

Screensavers do absolutely no good for an LCD, for the reason you
mentioned - the backlight is still always on full blast and consuming
power, no matter what.

I figured.

The LC material itself does not care if it's in
the "black" or "white" state ...

But if it's in the "black" state, it's absorbing light and heating up
the monitor more than in the "white" state, right?

Seriously, the best thing you can do for it is to simply shut
the thing down when it's not in use for extended periods, just
like a CRT.

So the burning question is: after how long a period of inactivity?

I've seen places go through fluorescent ceiling lamps like there's no
tomorrow, simply because they insist on turning them off every single
time they walk out of a room. Naturally, the lamps fail prematurely.
I'd like to find the ideal duty cycle for maximum life. Someone must be
studying this somewhere.

Assuming that in the power-save mode, the backlight is shut off,
there would be no difference. Being "completely shut off" would
save a bit on the rest of the monitor, i.e., the power supply,
interface components, etc., and so is preferable. However, in most
LCD monitors I'm familiar with, there is only one "power-save"
state anyway, and it essentially IS the same as "completely shut off"
- the only thing up and running is just enough circuitry to detect
active video starting up again, in order to bring the monitor OUT
of the power-save state. The backlight and inverter, and the interface
electronics (for the most part) would be completely shut down.

So skip the screensaver, and just set the power-saver time on the PC to
turn it off after some magic number of minutes or hours.

The LCD itself, no; there is with time the possibility of such things
as drivers failing, or even getting more stuck on/off pixels within the
panel, with age, but the basic visual performance does not change.
The exception to this is, again, the backlight, which will slowly lose
brightness with time and in that process possibly experience some
color shift (which could be compensated for, to some degree, via
the monitor's white balance controls if such are provided). For
the most part, though, everything stays LOOKING the same right
up to the point where it fails for good.

I suppose that's a good thing. I hope that by the time this one wears
out I'll be able to afford a replacement of at least equal quality.

Yes and no. The LCD panel itself is generally operated at a
fixed rate, or within a relatively small range of timings. The fact
that you can throw different video timings at the monitor has to
do with the scaling and frame-rate conversion capabilities of
digital ICs in the "front end" (the interface circuits), and again these
will either work or they won't - they will not slowly degrade with
time, in any way that affects the visible performance.

What is the actual refresh rate of a flat panel?

I used to run my CRT at very low rates, because I figured it extended
life, and because I don't seem to be sensitive to flicker. I had it set
to 60 Hz at 1600x1200. I just left it that way with the new flat panel.

One
possible exception would be drift in some of the front-end
components having to do with the stability of the sampling clocks
(generated by phase-locked loop circuits, somewhat as in a CRT
deflection circuit), so it is possible that the stability of the image
might slowly become poorer as, say, a capacitor or some such
external component aged. But it's not nearly as likely as in a
CRT; again, the general rule will be that things will work just fine
right up to the point where they fail completely, as is the case with
most digital equipment.

How does the flat panel manage to sync up with analog input? It seems
to get every pixel precisely positioned under a real pixel on the panel.

I also tried turning on ClearType, and it looks great!

Most often, this is controlling the backlight level; there may be
additional controls (perhaps labelled "contrast") which would
play around with the gray-scale range, i.e., how the panel is
actually being driven. Lower backlight brightness would extend
life somewhat; the latter sort of control would have essentially zero
impact on lifetime.

So maybe I should turn down the brightness. It's quite brilliant right
now.

 

[Bob Myers]

Do the backlights have heated filaments, or are they cold cathode types,
or what? As I recall, fluorescent lamps without heated filaments last
longer.

LCD backlighting is today almost always via cold-cathode
fluorescents. They DO last longer than the tubes lighting your
average office, but they're by no means immortal - and since
the generation of light is via a phosphor, there is also a
dimming-and-color-shifting-with-age sort of concern with any
such tubes.

Solid state backlighting and other technologies are coming, but
certainly are NOT mainstream yet (for the u$ual rea$on$)....

I worry mostly about some of the static elements of standard windows on
the screen; the buttons are always in the same place on full-screen
windows, and so on.

Generally not a problem. Again, the best thing to do for all of
this is to simply turn the thing off when it's going to be unused
for extended periods - such as, don't leave the monitors in the
office on when you go home for the evening.

But if it's in the "black" state, it's absorbing light and heating up
the monitor more than in the "white" state, right?

Well, the overall LC stack is absorbing more light, yes
(the actual blocking of the light occurs at the polarizers, not
within the LC material). But the heating effects are minimal,
since they're spead over such a large area. (I.e., the incremental
change is minor, compared to the heat the panel is receiving
anyway just from the backlight being on in the first place.)
In any event, though, there's little in the LCD that will be damaged
by this sort of heat in the first place - certainly the LC material
itself won't be affected, unless the heat would get well above
the level you're talking about here.

So the burning question is: after how long a period of inactivity?

Again, treat it much as you would a CRT. I wouldn't have the
"screen saver" (or whatever power-management features) set so
that the thing is being power-cycled every five minutes or so in
normal use, but I would certainly want it to be turned off if I were
going to be away for a few hours. Between those, a lot will
be determined by your work habits, and how annoyed you are
at having to restart the thing if you find the screen has gone black
on you. But don't overly-agonize about this; it's not worth the
stomach acid.

I've seen places go through fluorescent ceiling lamps like there's no
tomorrow, simply because they insist on turning them off every single
time they walk out of a room.

Right. So don't do that.

So skip the screensaver, and just set the power-saver time on the PC to
turn it off after some magic number of minutes or hours.

Right. For whatever it's worth, I currently have my desktop monitor
set to turn off after 20 minutes of inactivity. I figure by that time, it's
pretty clear that I'm away in a meeting or whatever, and the monitor
won't be needed for at least an hour. 10 minutes was just too short,
as often it would blank on me in the middle of a longish phone call
or some such.

What is the actual refresh rate of a flat panel?

It depends on the panel, but most are specified somewhere
in the 60-75 Hz range, with the majority tending to be at the
low end of that.

I used to run my CRT at very low rates, because I figured it extended
life, and because I don't seem to be sensitive to flicker.

That's the way to do it, for sure. Run the thing as low as
you can without YOU seeing flicker. If anyone else is
annoyed by this, consider it a feature, as it will keep people
away from your desk...

How does the flat panel manage to sync up with analog input? It seems
to get every pixel precisely positioned under a real pixel on the panel.

That was covered in another response I made today; if you need
more info after reading that, I'll go in to this in more detail.

So maybe I should turn down the brightness. It's quite brilliant right
now.

Right. Do what makes the screen look good FOR YOU. If it's
too bright for your tastes, you have nothing to lose by turning it
down.

I would follow the same recommendation in any case, including
making the tradeoff between image quality and comfort and the
life of the display. LCD monitors keep dropping in price, but
I don't see anyone offering to replace my eyes at ANY price...

Bob M.

 

[Mxsmanic]

Solid state backlighting and other technologies are coming, but
certainly are NOT mainstream yet (for the u$ual rea$on$)....

What ever happened to electroluminescent panels? I remember reading
about them years ago but they never seemed to gain any currency.
Wouldn't they be well suited to flat-panel displays?

Generally not a problem. Again, the best thing to do for all of
this is to simply turn the thing off when it's going to be unused
for extended periods - such as, don't leave the monitors in the
office on when you go home for the evening.

Agreed. This is what I'm currently doing. I'm always nervous when I've
spent every cent on new equipment and cannot afford to have it wear out
or fail.

Again, treat it much as you would a CRT.

Okay ... but I could never find a consensus on the question for CRTs,
either.

I wouldn't have the
"screen saver" (or whatever power-management features) set so
that the thing is being power-cycled every five minutes or so in
normal use, but I would certainly want it to be turned off if I were
going to be away for a few hours.

Right now I have the power-saver feature set to two hours, in case I go
out and forget to turn the monitor off. Otherwise, when I leave I turn
it off directly myself.

Between those, a lot will
be determined by your work habits, and how annoyed you are
at having to restart the thing if you find the screen has gone black
on you. But don't overly-agonize about this; it's not worth the
stomach acid.

At least flat panels are almost instantly on.

Right. For whatever it's worth, I currently have my desktop monitor
set to turn off after 20 minutes of inactivity. I figure by that time, it's
pretty clear that I'm away in a meeting or whatever, and the monitor
won't be needed for at least an hour. 10 minutes was just too short,
as often it would blank on me in the middle of a longish phone call
or some such.

Wow, that's really short. This is for a flat panel?

That's the way to do it, for sure. Run the thing as low as
you can without YOU seeing flicker. If anyone else is
annoyed by this, consider it a feature, as it will keep people
away from your desk...

I discovered the same advantage when I switched my mouse to the left
hand (mainly so that I could use my dominant right hand for the graphics
tablet--but discouraging other users was a nice side effect).

That was covered in another response I made today; if you need
more info after reading that, I'll go in to this in more detail.

I saw the other explanation, which was excellent.

 

[Bob Myers]

What ever happened to electroluminescent panels? I remember reading
about them years ago but they never seemed to gain any currency.
Wouldn't they be well suited to flat-panel displays?

Yes, and there have been some EL backlights. They've failed
to displace CCFLs for a number of reasons, including cost,
reliability, and efficiency. There are some good white ELs
available now which could come close to equalling a CCFL
backlight in these respects, but there's little chance they can
displace the CCFLs at this point. Getting rid of those will
have to wait for a truly superior technology to come along.
There ARE some candidates we might see in a few years,
such as purely solid-state lighting (LEDs).

Okay ... but I could never find a consensus on the question for CRTs,
either.

Yeah, well, display engineers are a prettty cagey bunch...

Wow, that's really short. This is for a flat panel?

Right; my current desktop monitor is a 17" LCD, at least
in the office. At home, it's a 19" CRT, just because it
still works just fine, I have the space, and I'm fundamentally
a cheap sort....


Bob M.