Date: Thu, 11 Oct 2001 15:54:47 +0800 From: Raymond <[EMAIL PROTECTED]> Subject: Re: [LIB] LCD brightness thing
>A little of what you wrote sunk in... through a lot that was bouncing off my thick >skull. I realized that I really know very little about just how LCD screens work. >Millions of transistors control millions of crystals that each display... either one >pixel ... or one color for a pixel ... or both. Actually, each 'pixel' is just set of 3 little LCD 'shutters' (liquid crystal and activated by electric field of course!) in front or behind 3 different colored filters. Varying the amount of light each 'shutter' lets through will give you variations in color. >Is there more than one crystal per pixel? Are there 3 crystals of different colors >focusing on one pixel on the surface of the screen? Probably not. Liquid crystal is probably a misnomer ... its not like each pixel is a crystal or anything like that, the crystals themselves are heaps smaller than a pixel. And there isn't any focusing being done iether. >I forgot much of what I read already. The controller makes the crystals actually >turn to let light pass through from what I understand. I guess each crystal has an >innate coloration, right? Yes and no. An electric field placed across the crystal makes it twist and the amount of twisting, along with the polarizers front and back, determine the amount of light let through by each pixel-element (of which there are 3 per pixel). >I would still think that if a MUCH brighter light source is shined through the >crystals, the color might get washed out. Well think about it THIS way. The LCD panel itself behaves like an OHP slide. You can put it on a light box and see whats happening. You can put it on an OHP and whilst you'd probably get blinded the colors themselves won't get 'washed out'. Likewise you can put that same OHP slide on a piece of white paper and also see whats on it. > Unless the crystals actually work like prisms that refract white light into bands >of color. Is that what's happening? Perhaps it's not like white light going through >a colored gel in front of a spotlight, as I initially thought. Nope, its pretty much like a colored gel with an electronically controlled incremental shutter on it. Except on the Libby screen there are 1920x480 of them (as there are 3 per pixel in the horizontal direction). >Then there's the deal of the different elements that make up different layers of the >LCD screen. You mentioned something about a 'layer' (my term) that I didn't >understand. I also read where there's supposed to be panel's of glass. Was that >ages ago before the plastic front surfaces? Or is there glass plates inside >somewhere. OK here's the layers of a PASSIVE MATRIX LCD as far as I'm aware: 1: Front anti-reflective layer (plastic) 2: Polarizing sheet (vertical polarization) (plastic) 3: Front electrical contacts (transparent tin oxide, most probably on a plastic substrate) 4: Liquid crystal layer (crystals suspended in some gel as far as I'm aware) 5: Rear electrical contacts (again transparent tin oxide, this time on a glass substrate) 6: Rear polarizing layer (this MAY in fact be behind the glass substrate, I'm not sure) 7: Glass substrate 8: Diffusion layer for the backlight Now you're probably wondering where the colored filters are and what about an active TFT screen as used in the Librettos. The colored filters could come anywhere between layers 3 and 6, I've got no idea where exactly (its probably on a webpage somewhere though). For a TFT screen, the actual transistors (which are transparent) *probably* sit on layer 5 but don't quote me on it. Now since there is that relatively thick glass substrate between layer 6 and layer 8, you'd get quite a parallax shift if you made layer 8 image reflective. If you made it diffuse reflective however it might work better. This is where the libby differs from reflective screen PDAs ... layers 3 and 5 are switched on PDAs like the black-and-white Palms and a touchscreen layer replaces layer 1 so the image forming layer (layers 3 through 5) are right up against the reflective layer. Hope this helps! (and if anyone sees any mistakes, do correct me, this is all coming off the top of my head at the moment!) - Raymond ************************************************************** http://libretto.basiclink.com - Libretto mailing list http://libretto.basiclink.com/archive - Archives http://www.picante.com/~gtaylor/portable/faq.html - FAQ -------TO UNSUBSCRIBE------- Reply to any of the list messages. The reply mail should be addressed to: [EMAIL PROTECTED] - Then replace any text on the message's subject line: cmd:unsubscribe --------TO UNSUBSCRIBE DIGEST------ Do above but with this on subject line: cmd:unsubscribe digest **************************************************************
