How do LCD displays work?

[apollo2011]

I was just wondering how an LCD display worked. I heard that they like water bubles and they pass certain ammounts of electricity through them to make them display the right color. I am not sure if all/some of that is correct.

[iglak]

read this (clicky) from THE BEST SITE EVAR!!!!!!!!!11 (besides SFN)

 

 

now, from your post on plasma, i think you mean plasma displays (clicky) , the two are different

[Dave]

LCD screens have lots and lots of leds in them. That's about it really (if only it were that simple).

[YT2095]

LCD (Liquid Crystal Display) have 2 polarised films and sandwitched in between is a liquid that becones orientated )like a crystal) on exposure to an electical charge, thus allowing the light to pass through unhindered

[Guest sam_mil90]

LCD stands for liquid crystal display and it definately doesn't use LED's which can emit only one colour, LED's are too big to make a quality picture because they are too big.

[apollo2011]

iglak:

No I meant LCD's. but learning how Plasmas work would be interesting too.

[Sayonara]

There is a "3D" LCD display in development. It's super funky.

 

It relies on specific perspective, so there are stupid constraints on how it's used (EG you have to sit in a certain position and not move), but as usual once the technology is there some bright spark will figure out how to improve it.

[apollo2011]

Yeah look at the first LCD Displays they had on Laptops.

You could only see the screen when you were right in front. Now you can see them from just about any angle.

 

Because of that now they have stupid little sheets that you slide onto your screen so people next to you (ex. on a plane) can't see what you are doing. You wouldn't need that if you were using one of the original displays. ;-)

[Kedas]

sam_mil90 said in post #5 :

LCD stands for liquid crystal display and it definately doesn't use LED's which can emit only one colour, LED's are too big to make a quality picture because they are too big.

 

uhmmm, LED's only one colour??

and about screen use:

http://www.universaldisplay.com/tech.php

http://www.zdnet.com.au/reviews/coolgear/av/story/0,2000023510,20273393,00.htm

[VendingMenace]

well, sam_mil90 was correct in his statement. LED's are typically only one color. The way you would get different colors is to put two or more of different color right next to eachother or on top of eachother. Then you would let the differnt colors blend to form form more colors.

 

Also, the links you provided are for OLED's wich are a bit differnt than you standard LED's. Standard LED's would not make for very sharp displays, and they are rather clunky things. The LED part is rather large, usually, and they must be encased in an epoxy.

 

OLED's on the other hand can be quite small, also, they can be encased in things that are quite flexible. Thus, they have the potential to make liightweight flexible monitors. (you could walk into a room, pull a sheet out of your pocket, unfold it and plug it into your computer as your monitor!). Of course OLED's are still a bit far off, at least from what i have heard. They are comming along, but they don't quite have the brightness and colors that the market would require. And besides, right now they don't really last all that long and would burn out kinda quickly.

[gene]

pass through in one plane?

[gene]

Actually, how can we make a liquid-crystal stage. loike making that object half liquid and half solid. Is it possible?

[gene]

YT2095 said in post #4 :

LCD (Liquid Crystal Display) have 2 polarised films and sandwitched in between is a liquid that becones orientated )like a crystal) on exposure to an electical charge, thus allowing the light to pass through unhindered

 

What do you mean by polarised films?

[YT2095]

imagine you`re in prison and the bars go from top to botom and are 6 inches apart. you have a pile plates 1 foot wide each. if you try throw them like a frisbee, they wont get past the bars.

if the bars were going Across instead, the plates would be able to pass through easily.

well consider light like it`s plates being thrown, and the bars as being the polarising film, only the light particles (plates) traveling on a certain plane will pass through it.

that`s why if you get 2 of these films and lay one on top of the other it will apear black if you rotate it 90 degrees, because the bars go top to botom and side to side, making a grid that no plate can escape from

hope that helps a little.

[gene]

Wonderful illustration. Thanks YT! i love it!

[YT2095]

n/p

 

and you may already know this, but the LCD in a laptop is backlit by flourescent tubes, similar to those in the hand held torches.

the type in your watch is passively lit, the back of the display has a reflective surface and uses ambient light to create the effect.

some others have an electro lumiescent backing or tiny (smaller than a match head) ordinary fillament bulb. in mobile fone displays, it`s an LED array, whose light follows a polycarbonate structure to evenly spread the light out (a bit like a fiber optic).

 

there`s a little bit more trivial data from the YT

[gene]

heh, seriously. i don't know these stuff... it is a bit too advanced for me.

Anyway, what is fiber optics?

 

THanks AGain~

[gene]

Btw, did you get the mail? I was wondering...

this is more of a personal stuff... so i sent it as PM.

[YT2095]

Fiber Optic, well it`s a wire basicly, except instead of it carrying electricity, is carries Light

 

originaly it was a type of Glass, nowadays it`s made of plastics, plastics that are very pure and have no little bits in it to block the light as it travels down it`s length.

maybe you`ve seen some and not realised it, have you seen these x-mas trees that light up all over the place but don`t have any bulbs that you can see?

those are fiber optic cables, they look a bit like realy thick fishing line.

 

nope, I`ve got no PM from you here yet?

[Kedas]

VendingMenace said in post #10 :

well, sam_mil90 was correct in his statement. LED's are typically only one color. The way you would get different colors is to put two or more of different color right next to eachother or on top of eachother. Then you would let the differnt colors blend to form form more colors.

 

Also, the links you provided are for OLED's wich are a bit differnt than you standard LED's. Standard LED's would not make for very sharp displays, and they are rather clunky things. The LED part is rather large, usually, and they must be encased in an epoxy.

 

OLED's on the other hand can be quite small, also, they can be encased in things that are quite flexible. Thus, they have the potential to make liightweight flexible monitors. (you could walk into a room, pull a sheet out of your pocket, unfold it and plug it into your computer as your monitor!). Of course OLED's are still a bit far off, at least from what i have heard. They are comming along, but they don't quite have the brightness and colors that the market would require. And besides, right now they don't really last all that long and would burn out kinda quickly.

 

- How can you put LED's of different colour besides each other if there is only one colour?

(you just proved my point.)

There are even IR LED's, obviously you can't make a full spectrum with one LED but any screen uses 3 base colours so no differents there.

 

- Yes OLED aren't the same as LED's but they have much more in common with LED's than with LCD's.

 

- I only have that site as reference but the only obvious disadvantage is lifetime (not brigthness)

And it is not so far away you can even buy some first devices with OLEDs.

[Sayonara]

Polarising plastics have a structure that allows light to pass through in one plane only.

[YT2095]

Kedas, it`s done by doping of the silicon on the same substrate with different carrier elements, it`s a single device with a common cathode and 3 anode inputs, Red Green and Blue, often accompanied by a sensor on the same substrate for detection of intensities (compensated for with an ASIC)

they DO exist

[Kedas]

Yeah, that what I'm trying to say the whole time. there are diff. colours.

(although I wasn't even mentioning that you can put them on the same substrate)

[YT2095]

I know you were, I was backing you up

[Kedas]

OK

 

Here some PDF info about materials and their corresponding wavelengths. (for the non believers)

http://alpha.qmul.ac.uk/~ugez644/MAT203/LEDs.pdf

 

 

EDIT:

and especially for people who like to see it but can't view PDF:

Common III-V materials used to produce LEDs and their emission wavelengths

Material Wavelength (nm)

InAsSbP/InAs 4200

InAs 3800

GaInAsP/GaSb 2000

GaSb 1800

GaxIn1-xAs1-yPy 1100-1600

Ga0.47In0.53As 1550

Ga0.27In0.73As0.63P0.37 1300

GaAs:Er,InP:Er 1540

Si:C 1300

GaAs:Yb,InP:Yb 1000

AlxGa1-xAs:Si 650-940

GaAs:Si 940

Al0.11Ga0.89As:Si 830

Al0.4Ga0.6As:Si 650

GaAs0.6P0.4 660

GaAs0.4P0.6 620

GaAs0.15P0.85 590

(AlxGa1-x)0.5In0.5P 655

GaP 690

GaP:N 550-570

GaxIn1-xN 340, 430, 590

SiC 400-460

BN 260, 310, 490