All right.
So, what are the pros and cons of using LCD display?
So, when I'm comparing these pros and cons, I'm really what I'm comparing it
against is this other competing technology which
is called OLED, or Organic Light Emitting Diodes.
And when I compare my LCD displays versus OLED.
So the first thing, the very first thing that I notice is
that, you know LCD display if I buy them in market are
much more cheaper. So if you go in Fry's and you try to buy a
TV, almost all of them would be LCD and you could buy them
at you know you can buy, easily buy a 32 inch LCD for less than 400 bucks, and
if you'd first of all, you wont you'll have
a difficult time finding these OLED display then even if
you find them, they'll cost you more than 3000$
or 4000$ for a similar, size as LCD display.
So as compared to OLEDs, LCDs are
definitely low cost and that has resulted from
a fact that, you know it's the very mature technology, people have been using it.
And they have been manufacturing it for, you know over two decades now.
So that has really brought down the cost, and it's a really low cost technology.
Secondly is the other important thing is that as compared to
OLEDs you know you get a higher resolution in LCD at the moment.
You know, you can very easily buy LCD which have,
you know resolution of over 300 pixel per inch.
And this is what Apple likes to call it.
Over 300 is what you call as retina display,
if you hold it 10 inch away from your eye.
And as compared to that, OLEDS currently have resolution of you know approaching
or less than 300 pixels per inch. So, they have,
at the moment, LCDs have you know, higher display, higher resolution as compared to
OLEDS. At the moment also they have
higher brightness, so you can easily get very high, brightness LCD display.
And the reason they achieved that, even though
the process of of of getting light through this,
this many layers is very inefficient.
You can get you know very bright back light.
So you can, there's no limit you know how bright a back light you can get.
And currently in market you can buy displays you know
which have, I know Nokia has one which has a.
A brightness of over a 1000 candela per meter square.
So currently you can buy these with very high brightness.
Even though they're not very efficient but
nobody complains about these displays being less bright.
Because you can essentially make your back light as bright as you want.
Now, so these are the pros, now, you know,
let's do a fair comparison and, let's look at all the drawbacks.
So, one of the main
drawbacks or, you know, one of the compromises that you get is that whenever
you want to make these colors or you want to increase the color gamut of your LCD.
There's a trade-off that which always occurs.
That is your color gamut versus your brightness always have a trade-off.
So the way you. Can increase
these color gamut, of these LCD displays.
You can make these RGB filters more strong, or more saturated.
And that would give you a higher color gamut.
But that comes at the expense that you know, each of these.
Filters, they're more strong.
They will only let even marginal amounts of light through them.
So they decrease overall brightness of your display,
so this color gamut increase is achieved at the
expense of reducing your brightness in your LCD display.
Another another disadvantage of these LCD display
is your backlight always has to be on.
So even when you want to generate black, your backlight has to be
on and you essentially, the way you generate black is you reject turn
each of these RGB pixels off, and but still you are, even if you have a very
black image, like you know something like which
is to your, the, the sketch board that I use.
That will, you know which is mostly have a
black background, your back light will always be on.
And, specially if you are generating, you know
if you have a image which is mostly black.
You still are using (power)
you're still consuming a lot of power to, display.
Another thing which I allready (mentioned), which, Is that these the contrast in these
LCD display is limited to something around 1,000 to 1,
and that comes from the fact that there is always
some light which leaks through, so there is always some light which
leaks through, and especially.
When you are turned the pixel off or you want to display a black thing,
it's always not black, it's more like a gray-black, and
that limits your overall contrast because, you know, you cannot completely
turn the pixel off, so your black is never 100% black, and that limits
your overall contrast to less than 1000 to 1.
And the,
the biggest limitation or you know, the biggest
drawback comes from this fact that
you have these many, many, many layers in
LCD display in each of these limits, your efficiency.
So you get less than 5% efficiency of your
of your photons from your back light which pass through.
And the backlight also has efficiency
of, you know, if it's LED it has an efficiency of,
you know, 20 to 30 percent, so, over all, converting your
light into how many photons that come out, it has, you
know, your LED, LCD-based display have a efficiency of 1 to 2%.
And having these many, many layers it also limits your viewing angle.
So passing lights through this many, many layers
when it finally comes out it, it is very, very directional.
So that limits your viewing angle and that is shown
in more detail in this picture over here, so this plot essentially
is the contrast for LCD cell and as you can see,
you have a contrast, a very high contrast that when you're viewing
it at a angle up here, so when you're viewing it at a normal angle.
You get this contrast of 800 to one that
I you know around, around thousand that's the maximum contrast you get
but, if you tilt your display, if you view it
at an angle, this contrast falls at a very sharp rate.
So even if you view it at you know, an angle of 20 degree.
From the normal, you already have decreased your contrast from 800 to 400.
And if you view it at a 60 degree angle, you get a contrast of only ten to one,
and that's, you know, that's something that you, you in
your human eye will have a very hard time distinguishing.
So the quality of this LCD display, or the quality of
the image, it falls very sharply as you increase your viewing angle.
So this, one of the latest development that has taken
place in the field of LCD, is motivated by improving this viewing angle.
And it's called in-plane switching display.
So to describe that, you know, I'm just describing
these two different schemes that are used that you
can use to control your liquid crystals.
The most common scheme is the Twisted Nematic scheme, which essentially means
that you have these two transparent
conducting electrodes, and these are perpendicular
to each other, and, you know, you could not apply a voltage
and there would be letting the liquid crystal, or let the light through.
Or you could apply
voltage over here, and the liquid crystal won't let any light through.
But these two electrodes, which are controlling your liquid crystal, they
are placed on the two sides of the liquid crystal, and.
That's a standard configuration which was used for many years
and it's called with twisted pneumatic configuration or a TN configuration.
One of
the limitations of this is that your light has to pass through this electrode and
it has to pass through this other
transparent electrode and you have essentially more layers.
You add more layers to your liquid crystal display.
Another thing is that if you if you if you, if
you add a touchscreen on the top and you apply some pressure
so some of that you know passes through that pressure
comes through your liquid crystal as well and when you.
Touch this top, you modulate this size, or volume of this liquid crystal.
It results in this thing called a tail.
When you say, you know, if you have a LCD monitor, try, you know, touching
it from the top and you see this tail, or you know, this phenomenon called a
tail which occurs when you. Press this LCD display on your monitors
and you apply a pressure on them. So one of the latest developments that has
taken place in the field of LCD displays is that people have
adopted this new technology called In Plane Switching.
So instead of having those two electrodes on the top and the bottom.
You have these
two electrodes placed side by side and they apply an electric field like this,
which bends your liquid crystal molecule, and you can control the liquid crystal
orientation by now having an electric field which is in the plane, instead of
having perpendicular to the plane, and that reduces, what it does is it
reduces one... Now you have, know you have, few layers
less, you don't have that other, other, conducting electrode placed on the top.
So you have less number of, layers. And a disadvantage (of this) is that now you have more of
your area occupied by these electrodes, so you degrade your fill factor slightly.
But you have less of these layers on the top,
also, you don't have that transparent conducting electrode on the top, so if you
press it from the top, now you don't get any tail in your viewing.
So one of the advantage that you get is pointed out in these figures.
So now that you have one you have less number of layers,
so you get a better viewing angle. So this picture over here it compares
Viewing angle between your IPS and your twisted Nematic so
you can see that for your twisted Nematic kind of configuration,
your contrast falls off very sharply and you get very
small viewing angle of less than 20 degree on each side.
Versus if if you have, if you use the IPS technology, now you
have less number of layers so you get a much larger viewing angle.
And, you know, especially this removal of this tail on the
top, especially even more important for your
for your smart phones and your tablets.
this was the IPS technology is very commonly used in in your
smart phones and your tablets which use which use these LCD based displays.
And,
you know, you can see this announcement from iPhone 4 a
keynote, and you know, Steve Jobs is saying that, you know,
they're using this they're switching to this IPS or In Plane Switching
technology and that helps them giving achieving a wider viewing angle.