Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

A high-end CRT gets fuzzy and dim anfter a couple of years.

How does a good LCD change with age and what is the limiting factor
for life ?

Does turning an LCD on and off frequently shorten the life. I have in
mind a laptop that has power saving set to trun the screen off after
15 minutes of activity.


Comments ?

--
a d y k e s @ p a n i x . c o m
----

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

"Al Dykes" <adykes@panix.com> wrote in message
news:cmauh7$4tm$1@panix5.panix.com...
>
> A high-end CRT gets fuzzy and dim anfter a couple of years.

Well, OK. Actually, what you are seeing here is the aging of the
cathode and phosphor screen, which combine to reduce the
brightness and change the operating characteristics of the
tube. (I.e., it doesn't HAVE to get "fuzzy," but the charactertistics
of the electron gun change such that the focus voltages provided
by the initial adjustment are no longer correct.) It's rarely worth
the trouble, though, to go through a complete readjustment of
the monitor given the main impact of all this aging, which is
to make the cathode a less efficient producer of electrons, and
the phosphor less efficient at converting them into light. This
typically means a lifetime for the CRT of something on the order
of 15-20,000 hours of operation. IF you left the thing running
all the time, that would be a couple of years (one year is
about 8800 hours), but then if you only use the thing 8 hours
a day, five days a week, this might be a useful life of 10 years
or so.


> How does a good LCD change with age and what is the limiting factor
> for life ?

The LCD itself - i.e., the inner workings of the panel, the action
of the liquid-crystal molecules themselves - doesn't really have
much in the way of aging mechanisms that degrade its performance,
assuming that there's no significant net DC voltage applied across
the material for extended periods of time (and this is true for
any drive scheme you're going to come across these days). So
it's tempting to say that the life of the LC itself, assuming that the
panel doesn't get mechanically stressed (cracked, etc.), or operated
under extreme temperatures is practically unlimited. However, what
you DO run into within the panel itself is the eventual failure of one
or more drivers (which will generally take out an entire row or
column of pixels), or (much less likely, but there's way more of them)
the failure of a transistor within the TFT "active matrix" array on the
glass (which knocks out a subpixel). Driver failures are generally
considered to fail the panel, whereas with subpixel losses, it's a
question of how many you can tolerate before you consider the
panel as "failed." In any event, once the "infant mortality" sorts of
fails are past (those failures that occur very early in the life of a
given component, generally due to something wrong in the
construction of that component that wasn't caught when it was
made), the cumulative MTBF of the panel is very likely at least
in the 50-100,000 hours range, meaning that it's very likely to
give you at least a 10 year useful life and possibly quite a bit
more. This again assumes no unusual stresses, either mechanical,
thermal, or electrical.

More likely than a panel failure by far is failure of one or more of
the backlight tubes, and/or the power supplies (you've likely got
at least two to deal with in an LCD monitor, namely the main
supply and the inverter which provides high voltage to drive the
backlights). Backlights of the CCFL type (cold-cathode
fluorescent, which most notebook and monitor panels will be
using) also DO age, similar to the way a CRT ages, meaning
that their light output goes down with time - so you may reach
a point where everything is working, but you find the display
unacceptably dim.

The bottom line, with all of these factors considered, is that
you currently see LCD monitors generally quoting an MTBF in
the low-to-mid tens-of-thousands of hours range, with the
limiting factors being the backlight tubes themselves, followed
by the inverter, power supply, and finally either panel or the
interface board. As with any electronics, mechanical and
thermal stresses outside the normal operating conditions will
shorten the life considerably.


> Does turning an LCD on and off frequently shorten the life. I have in
> mind a laptop that has power saving set to trun the screen off after
> 15 minutes of activity.

As with any electronics, turning the unit off for power-savings
reasons involves a tradeoff. You're trading straight aging
factors for the degradation that results from the on/off
transients. It's really hard to answer this question generally, as
a lot depends on just how often the unit is being power-cycled
vs. how long it would be left on an idle (i.e., burning time on the
"aging" clock, but not really doing anything useful). Turning off
after 15 minutes of inactivity isn't necessarily a bad thing, as long
as it's not being immediately turned back on each and every
time that happens, all day long. That's then the worst possible
case, as you get all of the aging AND the on/off transients.

Bob M.

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

Bob Myers wrote:
> .......
> More likely than a panel failure by far is failure of one or more of
> the backlight tubes, and/or the power supplies (you've likely got
> at least two to deal with in an LCD monitor, namely the main
> supply and the inverter which provides high voltage to drive the
> backlights). Backlights of the CCFL type (cold-cathode
> fluorescent, which most notebook and monitor panels will be
> using) also DO age, similar to the way a CRT ages, meaning
> that their light output goes down with time - so you may reach
> a point where everything is working, but you find the display
> unacceptably dim.
>
> The bottom line, with all of these factors considered, is that
> you currently see LCD monitors generally quoting an MTBF in
> the low-to-mid tens-of-thousands of hours range, with the
> limiting factors being the backlight tubes themselves, followed
> by the inverter, power supply, and finally either panel or the
> interface board. As with any electronics, mechanical and
> thermal stresses outside the normal operating conditions will
> shorten the life considerably.
> ...

White LEDs are getting pretty bright now, why don't LCD manufacturers
use LEDs for the backlight instead of the tubes? That would have much
higher lifespan(100000+ hrs for LEDS), better ruggedness (no brittle
glass tubes) and avoid the toxic materials in those tubes (probably mercury
in them?)
Mark

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

Gumby wrote:

> Bob Myers wrote:
>> .......
>> More likely than a panel failure by far is failure of one or more of
>> the backlight tubes, and/or the power supplies (you've likely got
>> at least two to deal with in an LCD monitor, namely the main
>> supply and the inverter which provides high voltage to drive the
>> backlights). Backlights of the CCFL type (cold-cathode
>> fluorescent, which most notebook and monitor panels will be
>> using) also DO age, similar to the way a CRT ages, meaning
>> that their light output goes down with time - so you may reach
>> a point where everything is working, but you find the display
>> unacceptably dim.
>>
>> The bottom line, with all of these factors considered, is that
>> you currently see LCD monitors generally quoting an MTBF in
>> the low-to-mid tens-of-thousands of hours range, with the
>> limiting factors being the backlight tubes themselves, followed
>> by the inverter, power supply, and finally either panel or the
>> interface board. As with any electronics, mechanical and
>> thermal stresses outside the normal operating conditions will
>> shorten the life considerably.
>> ...
>
> White LEDs are getting pretty bright now, why don't LCD manufacturers
> use LEDs for the backlight instead of the tubes?

It's not the LCD manufacturer, it's the manufacturer of the monitor that
decides. There are some with LEDs--they're fairly common on PDAs for
example.> That would have much

> higher lifespan(100000+ hrs for LEDS),

Not necessarily. White LEDs use a phosphor similar to fluorescents and I
believe that that phosphor ages.

> better ruggedness (no brittle
> glass tubes)

The "brittleness" of the glass tube (engineered glass can be tied in knots
or made to stop bullets) is secondary to the fragility of the LCD panel
itself.

> and avoid the toxic materials in those tubes (probably
> mercury in them?)

Very little. And LEDs have their own toxic materials--arsenic instead of
mercury.

> Mark

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

"Gumby" <none@xxxyy.com> wrote in message news:Ji7jd.949$rx5.304@trnddc06...
> White LEDs are getting pretty bright now, why don't LCD manufacturers
> use LEDs for the backlight instead of the tubes? That would have much
> higher lifespan(100000+ hrs for LEDS), better ruggedness (no brittle
> glass tubes) and avoid the toxic materials in those tubes (probably
mercury
> in them?)

Two major reasons: cost and power/thermal issues. LEDs
aren't as efficient (yet) as CCFLs, and they're definitely more
costly. They've started to show up more in smaller panels
(cameras, cell phones, PDAs, that sort of thing) already, and
will make it to TVs at the high end very soon (and will then
be working their way down the market to monitors and
notebook PCs).

But expect the TV/monitor/etc. LED backlight systems to
use RGB LEDs, not white. Having the separate colors
is generally more efficient, and gives a FAR better color
gamut. (Better, in fact, than any display that has been in
mainstream use to date!)

Bob M.

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

"J. Clarke" <jclarke@nospam.invalid> wrote in message
news:cmjja80k5i@news1.newsguy.com...
> Very little. And LEDs have their own toxic materials--arsenic instead of
> mercury.

That's not really much of a concern, though, when comparing
the environmental impact of LEDs vs. CCFLs; in the LEDs,
the quantity of the toxic element or compound is extremely
small, and it's very tightly bound. CCFLs, on the other hand,
contain free mercury.

Bob M.

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

Bob Myers wrote:

>
> "J. Clarke" <jclarke@nospam.invalid> wrote in message
> news:cmjja80k5i@news1.newsguy.com...
>> Very little. And LEDs have their own toxic materials--arsenic instead of
>> mercury.
>
> That's not really much of a concern, though, when comparing
> the environmental impact of LEDs vs. CCFLs; in the LEDs,
> the quantity of the toxic element or compound is extremely
> small, and it's very tightly bound. CCFLs, on the other hand,
> contain free mercury.

Which is less of a concern than organic compounds of mercury. Being "very
tightly bound" and being "nontoxic" are not the same thing.

> Bob M.

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

Bob Myers wrote:

>
> "Gumby" <none@xxxyy.com> wrote in message
> news:Ji7jd.949$rx5.304@trnddc06...
>> White LEDs are getting pretty bright now, why don't LCD manufacturers
>> use LEDs for the backlight instead of the tubes? That would have much
>> higher lifespan(100000+ hrs for LEDS), better ruggedness (no brittle
>> glass tubes) and avoid the toxic materials in those tubes (probably
> mercury
>> in them?)
>
> Two major reasons: cost and power/thermal issues. LEDs
> aren't as efficient (yet) as CCFLs, and they're definitely more
> costly. They've started to show up more in smaller panels
> (cameras, cell phones, PDAs, that sort of thing) already, and
> will make it to TVs at the high end very soon (and will then
> be working their way down the market to monitors and
> notebook PCs).
>
> But expect the TV/monitor/etc. LED backlight systems to
> use RGB LEDs, not white. Having the separate colors
> is generally more efficient, and gives a FAR better color
> gamut. (Better, in fact, than any display that has been in
> mainstream use to date!)

I can see where a system that uses RGB LEDs as pixels would have a good
color gamut, but I'm a little bit puzzled as to how that would give as
different color gamut when used as a backlight for an LCD than a white
phosphor would. As far as being "more efficient", the white phosphor LEDs
seem to give off more light per unit of power consumed than colored LEDs.

> Bob M.

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

"J. Clarke" <jclarke@nospam.invalid> wrote in message
news:cmq4f7084n@news3.newsgvy.com...
> Bob Myers wrote:
>
> >
> > "J. Clarke" <jclarke@nospam.invalid> wrote in message
> > news:cmjja80k5i@news1.newsgvy.com...
> >> Very little. And LEDs have their own toxic materials--arsenic instead
of
> >> mercvry.
> >
> > That's not really mvch of a concern, thovgh, when comparing
> > the environmental impact of LEDs vs. CCFLs; in the LEDs,
> > the qvantity of the toxic element or compovnd is extremely
> > small, and it's very tightly bovnd. CCFLs, on the other hand,
> > contain free mercvry.
>
> Which is less of a concern than organic compovnds of mercvry. Being "very
> tightly bovnd" and being "nontoxic" are not the same thing.

Nor did I say they were; bvt toxic compovnds are
not as mvch of a concern IF they are, and reliably will
be, kept away from possible leaching into grovndwater,
etc., whether it's throvgh physical containment (i.e.,
the material in qvestion is reliably sealed away) or
throvgh being chemically bovnd so tightly that it's
extremely vnlikely that any hazard will exist. That's
why the lead in CRTs, while it hasn't been an
ignorable hazard, has not been the concern that one
might initially think. It's contained within the glass, and
is abovt as likely to be a health hazard vnder typical
conditions as drinking from yovr grandmother's prized
lead crystal goblets wovld be.

Similarly, the arsenic that was mentioned as being a
concern for LEDs is both chemically bovnd vp, and
very vnlikely to leach ovt jvst for that reason, plvs
it's embedded in a metal and epoxy package. The
mercvry in CCFLs (or other flvorescents, for that
matter), is a LOT more likely to get ovt into the
environment and cavse problems. The mercvry content
in backlight tvbes, specifically, has been rather strictly
limited by variovs regvlatory agencies (the limits imposed
by the Evropean Union, vnder directive 2002/95/EC,
are the most commonly referenced). However, no
reqvirement for mercvry-free backlighting has been
imposed yet, becavse at this time the variovs national
and international agencies are more interested in
encovraging the move the LCD monitors, for energy-
efficiency reasons. And it's vnderstood that the
mercvry-free alternatives simply aren't economically
feasible at this time. Once solid-state backlights are
more cost-competitive, that sitvation may change.

Bob M.

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

"J. Clarke" <jclarke@nospam.invalid> wrote in message
news:cmq4f6084k@news3.newsguy.com...


> I can see where a system that uses RGB LEDs as pixels would have a good
> color gamut, but I'm a little bit puzzled as to how that would give as
> different color gamut when used as a backlight for an LCD than a white
> phosphor would.

Having a wide color gamut depends on having primaries
that are highly saturated - in other words, the colors are
as spectrally pure as possible. Ideally, the RGB primaries
would be purely monochromatic; completely saturated,
single-wavelength sources. But at present, lasers are about
the only way to get to something like that.

Filtering a white source generally gives a much smaller
gamut, since the white source (especially an incandescent
source, but also a "white" phosphor one) emits over a wide
range of wavelengths, and no practical color filters can
limit the light coming through the display to just a single
wavelength, or even a narrow band around the desired
wavelength. This results in primaries that aren't especially
pure, and therefore a smaller gamut. (Take a look at
where typical CRT phosphors, such as the EBU set, fall
on the CIE color space chart.)

LED sources are much better, because they DO emit in
such a narrow range anyway (generally not a single
wavelength, but there's a narrow range, generally with
one wavelength dominating), and that's made even purer
with the right set of color filters. So you wind up with a
much better gamut than is possible with a white source.

> As far as being "more efficient", the white phosphor LEDs
> seem to give off more light per unit of power consumed than colored LEDs.

If the goal were just to make white light, you'd be correct
(at least for now). But as noted above, the goal for a
color display is actually to put the most light possible into
a narrow band of wavelengths around the desired
primaries. RGB LEDs which match the color filters well
will always be better in that regard than starting with
a white source, since the color filters will in effect "throw
away" most of the light from a white source.

Bob M.

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

Bob Myers wrote:

>
> "J. Clarke" <jclarke@nospam.invalid> wrote in message
> news:cmq4f6084k@news3.newsguy.com...
>
>
>> I can see where a system that uses RGB LEDs as pixels would have a good
>> color gamut, but I'm a little bit puzzled as to how that would give as
>> different color gamut when used as a backlight for an LCD than a white
>> phosphor would.
>
> Having a wide color gamut depends on having primaries
> that are highly saturated - in other words, the colors are
> as spectrally pure as possible. Ideally, the RGB primaries
> would be purely monochromatic; completely saturated,
> single-wavelength sources. But at present, lasers are about
> the only way to get to something like that.

First, I fail to see how making the white light for the backlight from
"completely saturated, single wavelength sources" instead of a phosphor
improves the color gamut of LCD displays, and second, the difference
between an LED and a laser is a little bit of trimming and some mirroring.
You don't need a laser to get monochromatic light, you need a laser to have
_coherent_ light.

> Filtering a white source generally gives a much smaller
> gamut, since the white source (especially an incandescent
> source, but also a "white" phosphor one) emits over a wide
> range of wavelengths, and no practical color filters can
> limit the light coming through the display to just a single
> wavelength, or even a narrow band around the desired
> wavelength. This results in primaries that aren't especially
> pure, and therefore a smaller gamut. (Take a look at
> where typical CRT phosphors, such as the EBU set, fall
> on the CIE color space chart.)

So how does backlighting with colored LEDs improve this?

> LED sources are much better, because they DO emit in
> such a narrow range anyway (generally not a single
> wavelength, but there's a narrow range, generally with
> one wavelength dominating), and that's made even purer
> with the right set of color filters. So you wind up with a
> much better gamut than is possible with a white source.

Again, how? You have explained how it is possible to obtain broader gamut
if you are using the LEDs as the pixels, but we were discussing
backlighting. Or have you changed the topic without making it clear that
that was your intent?

>> As far as being "more efficient", the white phosphor LEDs
>> seem to give off more light per unit of power consumed than colored LEDs.
>
> If the goal were just to make white light, you'd be correct
> (at least for now). But as noted above, the goal for a
> color display is actually to put the most light possible into
> a narrow band of wavelengths around the desired
> primaries. RGB LEDs which match the color filters well
> will always be better in that regard than starting with
> a white source, since the color filters will in effect "throw
> away" most of the light from a white source.

Well that's nice. Next time you change the subject would you make it clear
that you are doing so?

> Bob M.

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

"J. Clarke" <jclarke@nospam.invalid> wrote in message
news:cms20901in@news4.newsguy.com...
> First, I fail to see how making the white light for the backlight from
> "completely saturated, single wavelength sources" instead of a phosphor
> improves the color gamut of LCD displays,

I'm not sure how I can make it any clearer without being
able to show you the spectral curves for the two types
of sources. You DO understand that the LEDs are much
"purer" sources of light of a given color than a white phosphor.
right? (White phosphors are actually generally a mix of
multiple different materials, and have emission peaks all over
the place. If they were truly broadband "white" emitters, as
an incandescent bulb is, the situation would be even worse.)

Take a look, for instance, at the emission spectra of various
"white" LEDs in:

http://www.lumileds.com/pdfs/techp [...] PCLEDs.PDF

and then compare these with the spectra of individual RGB
emitters, as in:

http://www.lumileds.com/pdfs/DS25.pdf

Remember, it's not just a matter of putting out light over
a given range, either, but rather maximizing the light output
within a very narrow range of wavelengths. Again, the individual
RGB emitters matched to the color filters in use (actually, the
matching generally goes the other way around) is the best way
to achieve this.

LumiLEDs also has an excellent paper on the whole solid-state
backlighting notion in general, which you can find at:

http://www.lumileds.com/pdfs/techp [...] rLEDTV.PDF


> and second, the difference
> between an LED and a laser is a little bit of trimming and some mirroring.
> You don't need a laser to get monochromatic light, you need a laser to
have
> _coherent_ light.

As you'll see in the emission spectra shown in the documents
above, plain LEDs are NOT truly monochromatic sources. They
have a strong dominant wavelength, but there is also significant
emission to either side of this point. A laser does produce light
which is coherent (whereas the "plain LED" does not), but the same
phenomena which cause it to be coherent also mean that 's it a
much better monochromatic light source. The difference in
theory may be "a little bit of trimming and some mirroring," but
so far there's no good way to use laser sources in backlighting
applications in a practical sense.

>
> Again, how? You have explained how it is possible to obtain broader gamut
> if you are using the LEDs as the pixels, but we were discussing
> backlighting. Or have you changed the topic without making it clear that
> that was your intent?

Nope. Using the LEDs as pixels and using the LEDs as
backlighting gives very similar results - remember, the point
is saturated primaries, and putting the color filters over the
LED backlight (which admittedly appears to be making "white"
light) gets a lot closer to that than those same filters over a
more broadband source, such as a white-phosphor-based
emitter. Actually using the LEDs as the subpixel sources would
be even better, but clearly isn't practical for anything other
than very large displays. (You can also do better by going
to a field-sequential drive and illumination scheme, simply
because then the filters won't ever have to deal with the
"wrong" colors, but that's another can of worms.)

> > If the goal were just to make white light, you'd be correct
> > (at least for now). But as noted above, the goal for a
> > color display is actually to put the most light possible into
> > a narrow band of wavelengths around the desired
> > primaries. RGB LEDs which match the color filters well
> > will always be better in that regard than starting with
> > a white source, since the color filters will in effect "throw
> > away" most of the light from a white source.
>
> Well that's nice. Next time you change the subject would you make it
clear
> that you are doing so?

Sorry, no change of subject made. The point of a
backlight system for any color LC display, if the goal
is brightness and wide gamut, is NOT to make white,
but to provide the most light out through the color
filters. A true (broadband) white source will not be
the best way to do this.

Bob M.

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

Bob Myers wrote:

>
> "J. Clarke" <jclarke@nospam.invalid> wrote in message
> news:cms20901in@news4.newsguy.com...
>> First, I fail to see how making the white light for the backlight from
>> "completely saturated, single wavelength sources" instead of a phosphor
>> improves the color gamut of LCD displays,
>
> I'm not sure how I can make it any clearer without being
> able to show you the spectral curves for the two types
> of sources. You DO understand that the LEDs are much
> "purer" sources of light of a given color than a white phosphor.
> right? (White phosphors are actually generally a mix of
> multiple different materials, and have emission peaks all over
> the place. If they were truly broadband "white" emitters, as
> an incandescent bulb is, the situation would be even worse.)
>
> Take a look, for instance, at the emission spectra of various
> "white" LEDs in:
>
> http://www.lumileds.com/pdfs/techp [...] PCLEDs.PDF
>
> and then compare these with the spectra of individual RGB
> emitters, as in:
>
> http://www.lumileds.com/pdfs/DS25.pdf
>
> Remember, it's not just a matter of putting out light over
> a given range, either, but rather maximizing the light output
> within a very narrow range of wavelengths. Again, the individual
> RGB emitters matched to the color filters in use (actually, the
> matching generally goes the other way around) is the best way
> to achieve this.
>
> LumiLEDs also has an excellent paper on the whole solid-state
> backlighting notion in general, which you can find at:
>
> http://www.lumileds.com/pdfs/techp [...] rLEDTV.PDF
>
>
>> and second, the difference
>> between an LED and a laser is a little bit of trimming and some
>> mirroring. You don't need a laser to get monochromatic light, you need a
>> laser to
> have
>> _coherent_ light.
>
> As you'll see in the emission spectra shown in the documents
> above, plain LEDs are NOT truly monochromatic sources. They
> have a strong dominant wavelength, but there is also significant
> emission to either side of this point. A laser does produce light
> which is coherent (whereas the "plain LED" does not), but the same
> phenomena which cause it to be coherent also mean that 's it a
> much better monochromatic light source. The difference in
> theory may be "a little bit of trimming and some mirroring," but
> so far there's no good way to use laser sources in backlighting
> applications in a practical sense.
>
>>
>> Again, how? You have explained how it is possible to obtain broader
>> gamut if you are using the LEDs as the pixels, but we were discussing
>> backlighting. Or have you changed the topic without making it clear that
>> that was your intent?
>
> Nope. Using the LEDs as pixels and using the LEDs as
> backlighting gives very similar results - remember, the point
> is saturated primaries, and putting the color filters over the
> LED backlight (which admittedly appears to be making "white"
> light) gets a lot closer to that than those same filters over a
> more broadband source, such as a white-phosphor-based
> emitter. Actually using the LEDs as the subpixel sources would
> be even better, but clearly isn't practical for anything other
> than very large displays. (You can also do better by going
> to a field-sequential drive and illumination scheme, simply
> because then the filters won't ever have to deal with the
> "wrong" colors, but that's another can of worms.)
>
>> > If the goal were just to make white light, you'd be correct
>> > (at least for now). But as noted above, the goal for a
>> > color display is actually to put the most light possible into
>> > a narrow band of wavelengths around the desired
>> > primaries. RGB LEDs which match the color filters well
>> > will always be better in that regard than starting with
>> > a white source, since the color filters will in effect "throw
>> > away" most of the light from a white source.
>>
>> Well that's nice. Next time you change the subject would you make it
> clear
>> that you are doing so?
>
> Sorry, no change of subject made. The point of a
> backlight system for any color LC display, if the goal
> is brightness and wide gamut, is NOT to make white,
> but to provide the most light out through the color
> filters. A true (broadband) white source will not be
> the best way to do this.

Could you describe the geometry of whatever it is that you are proposing?
>
> Bob M.

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

"J. Clarke" <jclarke@nospam.invalid> wrote in message
news:cmtvhi02ssf@news1.newsguy.com...
> Could you describe the geometry of whatever it is that you are proposing?

Well, it's not exactly what I am proposing, personally, but
rather the way solid-state backlighting is currently being
planned for TV and high-end monitor panels. Again, the
most concise resource I can point you to with a good
coverage of the basics of this is the LumiLEDs paper
referenced in my last posting. However, the basic
geometry of this, for large-screen LCD backlighting, is
generally an array of LEDs (either separate R, G, and
B packages, or possibly tricolor single-package emitters
(if the thermal issues can be dealt with), either located
behind or embedded within a diffuser. (LumiLEDS has
a rather elegant "side-emitting" package designed for
just this application - you embed a bunch of those into
the diffuser, and the light goes almost entirely out the sides
into the diffuser before eventually being scattered "up"
through the LCD. This better ensures that you get a
uniform backlight, rather than annoyingly intense point
sources!)

Smaller panels, such as cell phones, PDAs, etc. (where
solid state backlighting is already becoming popular) and
notebook PCs are more likely to use a side-light sort of
configuration, with the LEDs arranged as a strip along one
side (or maybe two sides) of the module, sending light into
a diffuser/reflector on the back of the LCD panel (the diffuser
then mixes the light for uniformity and sends it "up" through
the LCD).

Note that the end result is a backlight which, if seen without
the LCD over it, would still look to the eye like a bright,
uniform, white plane - the difference between it, though, and
a normal "white" backlight is that the light coming out actually
has the energy primarily concentrated in three narrow peaks,
as opposed to being spread over the visible spectrum.

I hope that clarified things!

Bob M.

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

Bob Myers wrote:

>
> "J. Clarke" <jclarke@nospam.invalid> wrote in message
> news:cmtvhi02ssf@news1.newsguy.com...
>> Could you describe the geometry of whatever it is that you are proposing?
>
> Well, it's not exactly what I am proposing, personally, but
> rather the way solid-state backlighting is currently being
> planned for TV and high-end monitor panels. Again, the
> most concise resource I can point you to with a good
> coverage of the basics of this is the LumiLEDs paper
> referenced in my last posting. However, the basic
> geometry of this, for large-screen LCD backlighting, is
> generally an array of LEDs (either separate R, G, and
> B packages, or possibly tricolor single-package emitters
> (if the thermal issues can be dealt with), either located
> behind or embedded within a diffuser.