This isn't really the right forum for this Q&A but I'll try to explain this a little better. Kevin is right in most respects, LCD's work by having two polarized filters one oriented and one variable, by turning the variable one you control how much of the light from the flouresent bulb in the back gets through to the viewer.
But the principle behind anti-glare filters is to eliminate glare by polarizing the external sources of light and then blocking them after they reflect off the screen. One easy way to do this is to just stick a linear polarizer and a quarter wave plane in front of the screen (usually bonded into one sheet, called a circular polarizer)*. But this doesn't work with LCD's because you need to exactly align the external linear polarizer with the oriented linear polarizer in the LCD screen itself, if you don't you get all sorts of artifacts. *the circular polarization flips on reflection. Light that enters the space between the filter and screen reflects once off the glass and then either gets reflected or absorbed on it's attempt to exit, since it is now in exactly the wrong orientation to get through the filter. The light that is reflected off the back of the anti-glare filter hits the screen again, but this is an odd number of reflections again so it can't get out now either, repeat... To really get an anti-glare filter to work you would need to build it into the screen and precisely align it, read expensive. Instead LCD's are built with matted screens which diffuse the light hitting your screen and usually work for small to moderate levels of glare. Because they are built with these matted screens even a preciesely aligned filter would not work. The LCD screen being made out of a lightweight plastic also helps.. they are out of a similar material as the antiglare filters themselves, but you are still restricted more in your material than in the material for an anti-glare filter. Anti-glare filters work well with monitors because they emit unpolarized light (though this means the filter cuts your brigtness/contrast to less than half, which it wouldn't with an LCD), and because the screens have a highly specular, read smooth, screen. If you have one of those perfectly flat CRT monitors with a good anti-glare filter you could sit in the desert all day and never notice any glare. (the filter itself can glare, but this is something you control for when you pick the material for your filter, it does not need the material strength of the tube material (dense glass)) OLED and plasma displays could work with anti-glare filters, but here you cut the light in half which would nearly double the battery consumption so you won't see this on any future laptops, near-term anyway. However, this might mean you can put the flat-screen HDTV of the future in a sunlit room. I think maybe we'll get anti-glare filters built into LCD screens someday, but probably not until battery and heat dissipation technologies allow a much brighter lightbulb behind the LCD. As Kevin points out, most screens will be pretty washed out in the sunlight anyway because the backlight is so comparatively weak. The advantage of an anti-glare filter with LCD over say OLEDs is that you wouldn't get the additional 50% light loss because the light is already polarized, the alignment issue could be overcome with a sturdy metal frame, some cross supports and that same alignment technology that allows us to make microchips at all. There would be extra weight but maybe with lightweight alloy... it's not an insurmountable engineering problem, but trying it at home is probably a waste of time... My solution for computing out in the sun is to sit under a tree. My solution in the office is to close the blinds. Healthy skin has a slightly greenish hue. ;) -- Daniel On Thu, 3 Jul 2003, Kevin Arima wrote: ]On Wed, 2 Jul 2003, Jon Baer wrote: ] ]> can anyone make a good recommendation for an anti glare for a laptop? ]> ]> i thought id be able to buy some film (vs. attachment) but not the case and ]> id like it to fit my thinkpad snug and not flimsy ... something like ... ]> ] ]Err, might I ask *why* you need it? ] ]What anti-glare filters do is to polarize light that passes through the ]filter. Since CRTs are emissive, you do not lose as much "light" that is ]generated by the CRT (unpolarized->polarized), but cuts down on glare ]considerably (outside source->polarized->bounce off CRT glass->filtered by ]anti-glare). ] ]Since LCDs are non-emissive, it work by polarizing and twisting a source ]of light (backlight->first polarizing film->color film->crystal->second ]polarizing film). The crystal determines how much "light" will pass ]through by "twisting" the light so it either passes through or gets ]filtered by the second polarizing film. ] ]If you are having trouble reading the screen outdoor, that is because the ]ambient light is overpowering what the LCD provides, similar to how a ]flashlight is less effective at daylight than it is at night. Reading an ]LCD is like having a piece of paper that has print on the "back side" of ]the page and you need to shine a light through in order to read it. ]"Your" light has to be stronger than the ambient light. Anti-glare will ]NOT fix that. Either turn up the brightness, or read below for a "cheat". ] ]If you have glare "indoors" (true glare - ie, what you would experience ]with CRT), then the only thing I can recommend is reorient the laptop, or ]change the angle of the screen. But I have a feeling this isn't what you ]were referring to. ] ]Now, for the cheat. Forget filters. You can improve the readability of ]your screen with ~$2 or less of parts, and it doesn't have to look ]half-bad. Get yourself some black heavy-duty construction paper. You ]need to create an overhang, similar to this: ] ]http://www.necmitsubishi.com/products/home/ProductDetail.cfm?product_id=254 ] ]This will cut down the side light, and give you more angle where the ]screen is "viewable" outdoors. ] ]Kevin "Starfox" Arima ]-- ]NYCwireless - http://www.nycwireless.net/ ]Un/Subscribe: http://lists.nycwireless.net/mailman/listinfo/nycwireless/ ]Archives: http://lists.nycwireless.net/pipermail/nycwireless/ ] -- -- Daniel << When truth is outlawed; only outlaws will tell the truth. >> - RLiegh -- NYCwireless - http://www.nycwireless.net/ Un/Subscribe: http://lists.nycwireless.net/mailman/listinfo/nycwireless/ Archives: http://lists.nycwireless.net/pipermail/nycwireless/
