Does anybody know the actual name of that LCD technology that produces a 
monochrone display of light blue and dark purple? (And, incidentally, is 
usually scored with horizontal or vertical lines that shouldn't be there...)

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> Does anybody know the actual name of that LCD technology that produces a 
> monochrone display of light blue and dark purple? (And, incidentally, is 
> usually scored with horizontal or vertical lines that shouldn't be 
> there...)

You mean like this?

http://www.crystalfontz.com/phpthumb/phpThumb.php?id=806

It's a transmissive passive matrix TN display.  Same as you get in 
calculators or watches, except it controls the amount of light that can come 
through from the backlight, rather than how much is reflected.  The blue is 
because when the pixel is "off" it's only tuned to block out green light 
(the brightest wavelength), so some blue (and a bit of red) manage to get 
through.

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scott wrote:
>> Does anybody know the actual name of that LCD technology that produces 
>> a monochrone display of light blue and dark purple? (And, 
>> incidentally, is usually scored with horizontal or vertical lines that 
>> shouldn't be there...)
> 
> You mean like this?
> 
> http://www.crystalfontz.com/phpthumb/phpThumb.php?id=806

The ones I've seen are a lot more purple than that, but yeah...

> It's a transmissive passive matrix TN display.

OK.

> Same as you get in 
> calculators or watches, except it controls the amount of light that can 
> come through from the backlight, rather than how much is reflected.

Yeah, those usually just have a silvered back. And, depending on what it 
is, they don't always turn completely transparent when "off". (E.g., the 
phone on my desk has an 8x8 grid of pixels, and you can see where the 
pixels are even when they're supposed to be off. They do turn very, very 
black when they're on though.)

> The 
> blue is because when the pixel is "off" it's only tuned to block out 
> green light (the brightest wavelength), so some blue (and a bit of red) 
> manage to get through.

Hmm, I see.

We have several items of equipment here that have screens like this. I 
first saw them in laptops, about 20 years ago. But now you see them as 
touch-screen controls for photocopiers and the like.

And then, at home I have a keyboard that has a backlit LCD. But it's 
yellowy-green, with black pixels...

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scott wrote:

> It's a transmissive passive matrix TN display.

TN = Twisted Nemetic?

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> Yeah, those usually just have a silvered back. And, depending on what it 
> is, they don't always turn completely transparent when "off". (E.g., the 
> phone on my desk has an 8x8 grid of pixels, and you can see where the 
> pixels are even when they're supposed to be off. They do turn very, very 
> black when they're on though.)

Only if you look at them from exactly the right angle :-)

> We have several items of equipment here that have screens like this. I 
> first saw them in laptops, about 20 years ago. But now you see them as 
> touch-screen controls for photocopiers and the like.

Yes, they are very cheap compared to higher performance displays.  Not just 
the actual LCD, but also the drive electronics required is much simpler.

> And then, at home I have a keyboard that has a backlit LCD. But it's 
> yellowy-green, with black pixels...

The "colour" of a monochrome display is just the combination of the LED 
colour used in the backlight, and what wavelength the LCD is tuned to block. 
I guess there are common combinations, but pretty much anything should be 
possible.

> TN = Twisted Nemetic?

Yes

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>> Yeah, those usually just have a silvered back. And, depending on what 
>> it is, they don't always turn completely transparent when "off". 
>> (E.g., the phone on my desk has an 8x8 grid of pixels, and you can see 
>> where the pixels are even when they're supposed to be off. They do 
>> turn very, very black when they're on though.)
> 
> Only if you look at them from exactly the right angle :-)

Hmm, yes... Apparently if I stand in front of my desk phone, all the off 
pixels become completely transparent.

Why is LCD angle-dependent in the first place?

>> We have several items of equipment here that have screens like this. I 
>> first saw them in laptops, about 20 years ago. But now you see them as 
>> touch-screen controls for photocopiers and the like.
> 
> Yes, they are very cheap compared to higher performance displays.  Not 
> just the actual LCD, but also the drive electronics required is much 
> simpler.

I'm guessing making it touch-sensitive makes it more expensive though? 
(How the hell do they do that anyway? And how come the display doesn't 
"ripple" when you do this?)

>> And then, at home I have a keyboard that has a backlit LCD. But it's 
>> yellowy-green, with black pixels...
> 
> The "colour" of a monochrome display is just the combination of the LED 
> colour used in the backlight, and what wavelength the LCD is tuned to 
> block. I guess there are common combinations, but pretty much anything 
> should be possible.

So the keyboard probably has a green backlight and green liquid crystals?

I was under the impression that high-performance displays (e.g., my 
computer monitor) use florescent lighting rather than LEDs. (Although, 
obviously, I don't design LCDs for a living...)

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> Why is LCD angle-dependent in the first place?

Look at a picture of how TN molecules are orientated inside the LCD, eg 
here:

http://img.tfd.com/cde/LCD.GIF

When light is not going perpendicularly through, the LC obviously has a 
different effect on the light.

TN happens to be very bad for this, there are of course better ideas, one is 
called multi-domain vertical alignment:

http://www.pctechguide.com/images/43mva.gif

Simply put, it splits the pixel into several sub-parts, each aligned a 
different way, so when you see the pixel overall it looks the same from all 
viewing angles.

> I'm guessing making it touch-sensitive makes it more expensive though?

Of course.

> (How the hell do they do that anyway?

Stick a touch panel on the front.

> And how come the display doesn't "ripple" when you do this?)

Because there's an air gap between the TP and LCD, unless you press really 
hard then the TP might hit the front of the LCD.

> I was under the impression that high-performance displays (e.g., my 
> computer monitor) use florescent lighting rather than LEDs. (Although, 
> obviously, I don't design LCDs for a living...)

CCFLs are being replaced by LEDs, mainly because CCFLs contain mercury.  It 
started off with small size displays, but recently even TVs are using LEDs 
now.  LEDs have pros and cons compared to CCFL, but the only real cons are 
that it's harder to spread out the light evenly from a point source, and 
they get dimmer at high temperatures (watch out for positive feedback!).

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Am 31.03.2010 12:48, schrieb Invisible:

> Why is LCD angle-dependent in the first place?

LCDs (at least the older ones) use an effect of various materials (which 
can be controlled by an electrical current in the case of LCs) to 
"twist" the polarization direction of light passing through. The LCs are 
sandwiched between two polarizing filters, the first of which is used to 
polarize the light source, and the second to filter out part of the 
light depending how much "twist" it has experienced. (In passively-lit 
LCDs, a single polarizing filter may serve both roles.)

Obviously the twisting effect does not only depend on voltage applied to 
the LC, but also on the distance the light travels through it - which in 
turn depends on the viewing angle.

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