To be pedantic, theliquid crystals are not a "polarised light source."
The light comes from a uniform light at the back of the screen. This is polarised by a filter and then passed through the liquid crystal matrix. The crystals that are powered twist the polarisation 90 degrees. The light then passes through a second polarisation filter at 90 degrees to the first. If no twist is involved the light is stopped by that and the pixel is black. If the liqid crystals have twisted the light, however, the light passes through and appears bright. Colour is created by a mask layer of red, green and blue dots in register with the pixels, so each screen pixel is made up of at least three liquid crystal elements; one for each primary colour. The liquid effect when you touch the screen is caused by the pressure deforming the whole thing and compressing the liquid crystal layer, which is, after all, liquid. Nice trick: try looking at an LCD display of any sort, including a calculator or a watch, with polaroid sunglasses on. At some angle the whole display goes dark because the polarised light is at right angles to the polariod filter in the glasses. On Wednesday 27 Aug 2003 11:26 am, Tony S. Sykes wrote: > Exactly. > > -----Original Message----- > From: John Richard Smith [mailto:[EMAIL PROTECTED] > Sent: Wednesday, August 27, 2003 12:06 PM > To: [EMAIL PROTECTED] > Subject: Re: [newbie] Dell TFT 17"Flat Screen > > > Now that is an interesting article. So a pixel is really light bent > by electronic switching of the crystalls that act as polarised light > sources. I quess that is why if you run your finger lightly over the > serface of a LCD monitor you get a kind of watery effect of the > picture. What I didn't find clear was whether each polarised light > source is assigned a specific colour source or whether a given > crystal can be made to emit either of the 3 primary colours. > > > Anyway the essense of the matter as to how good a picture you are > going to get is the number of pixel polarised light sources per given > area and the speed by which those polarised light sources can be > switched on and off. Yes ? > > John > > stormjumper wrote: > >hi John, > > > >er, just a slight correction here. > > > >a typical basic specfication for a crt is the vertical refresh rate. > >i believe that is what u're referring to when you mentioned 85. > >it should probably read as 85hz, ie 85 cycles per second. > > > >a typical recommended comfortable value for most pp is 75, > >altho that requirement goes up as the screen gets larger. > > > >fyi, this refresh rate value has nothing to do w sharpness. > > > >most consumer LCDs are generally sharper than consumer CRTs, > >hence being easier on the eyes. some frens in certain creative > > fields, namely design and architecture, claim that the "pro" CRTs > >(typically 19" and above) are equally sharp, if not sharper. > >these obviously come at non-consumer prices as well. > > > >also, vertical refresh rate is not really relevant for LCDs. > >you can refer to > > > >http://www.lcdmonitors.philips.com/lcdmonitors/articles/basics_of_lc > >d.a > > sp > > > Why is a vertical frequency of 60 Hz optimal for an LCD monitor? > >which will explain far better than i can. > > > >for LCD's the more relevant spec is prolly the response time, > >which is a figure typically between 15-40 ms. > >the smaller the number, the better for watching video/playing games, > >as it will result is less visual streaking/smearing/watever you call > > it. > > >you should also take note of the brightness and contrast ratio, > >which is impt esp if you work in a very well-lit environment, > >eg a sun lit room. otherwise, most lcds are "bright enough". > > > >enuff said. hope these help. > >----- Original Message ----- > > From: "John Richard Smith" <[EMAIL PROTECTED]> > > >To: <[EMAIL PROTECTED]> > >Sent: Tuesday, August 26, 2003 20:46 > >Subject: Re: [newbie] Dell TFT 17"Flat Screen > > > >>I see, so in regards to TFT's it's not a case then of a beam of > >>electrons scanning the screen top left to botton right so many > >> times a second ( CRT of 85Mhz = 85 refershed scans per second) but > >> a question > > of > > >>how many times a pixel is electronically swithced on and off > >>electronically, that is by a circuit behind that pixel ? > >> > >>So a TFT with a refresh rate of 16ms is being switched on and > >> off, 16/1000of a second each time. I guess as time goes on that > >> time will decrease some as technology improves. > >> > >>Yes, I think Dell merely badge someone elses make don't they, they > >> buy in large orders at a time at best prices and badge them, and > >> sometimes they get a bad deal, and sell the shipment off quickly > >> to a retailer > > for > > >>a knockdown price. That is why I was suspicious in the first place, > > and > > >>came to the list, because I have extremely limited experience with > > these > > >>devices. Seems like I will have to keep my old CRT's a while longer > > yet. > > >>John -- Richard Urwin
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