I have seen that most laptops nowdays have a natural resolution of 1024x768 with a refresh rate of 60 hz.
Now how is it that notebook companies say that laptops are good for reading and doing all sort of office work when the screen has such low refresh rates?

If you change the resolution to anything other than the natural resolution then everything is sort of, well 'blocky' is the best word to describe ot.

What i dont understand is how is one supposed to use a laptop for long periods and as a replacement for desktops if the screen refresh rate is so low?
Posted on 2003-02-13 02:14:35 by clippy
Refresh rate has a different meaning for TFTs and CRTs. In a CRT, electron beams will 'paint' the screen pixel by pixel, line by line. This happens at a certain rate and this rate is called the refresh rate (you probably already knew this). Because the phosphor that is lit by the electron beam slowely fades, it needs to be lit again fast before it will be totally fade out. As the refresh rate increases, the phosphor gets less time to fade out and the screen flickers less.

However in TFTs, each pixel can be controlled seperately at more or less the same time, and they don't fade. So a TFT screen doesn't really refresh its screen until you change something. Usually, the refresh rate in the context of TFTs means the rate at which the videocard provides the frames. What's much more important is the response time. This is the time that a pixel takes to completely fade in from black to white (the rise time) and to completely fade out again to black (the fall time). The lower this time is, the smoother your screen is (less ghosting/smeering). But even if this time is high, the screen won't flicker. It's perfectly still. It will just appear awful if the screen image changes fast (like video, games or smooth scrolling).

TFTs only operate well on there native resolution because the pixels are actually physically on the screen (a 15" LCD usually has 1024 x 768 pixel elements (with 3 subpixels each). So if you have a horizontal resolution of 800, it needs to interpolate it to 1024 pixels (this can be done with various algorithms, some look awful, some look quite good, it depends on your monitor quality). A CRT doesn't have fixed pixels, it just manipulates the electron beam more often at higher resolutions.

Thomas
Posted on 2003-02-13 02:31:46 by Thomas
so does that basically mean that a notebook with a refresh rate of 60hz would be pretty easy on the eyes?
What refresh rate would be equivalent to of a CRT monitor( eg 85hz,70hz???)
Posted on 2003-02-14 02:23:28 by clippy
If nothing in changing then the TFT's refresh is like infinite CRT refresh, but if the image is changing then it's 60hz.
Posted on 2003-02-14 08:44:40 by bitRAKE

If nothing in changing then the TFT's refresh is like infinite CRT refresh, but if the image is changing then it's 60hz.


If the TFT specs say it has a refresh rate of 60Hz this usually is higher than the maximum possible screen changes per second (black-white-black). A common response time for modern TFTs is 20ms, which means it can change the image 50 times a second max (1/0.020s)). The 60Hz is then not referring to (1/response time) but to the frequency of the data stream at the monitor's input (often a range is specified, like 50~80Hz). Slow image changes aren't hard on the eye, it just appears slow. Low refresh rates on a CRT *are* bad for your eyes.

Thomas
Posted on 2003-02-14 14:42:14 by Thomas
talking about laptops there's a sweet new one (I think by toshiba) with a turnable screen that can become a sort of big PDA :)
Posted on 2003-02-14 14:47:50 by Hiroshimator
my monitor doest use a cathode ray tube, LCD baby!
Posted on 2003-02-14 14:59:57 by Qages

talking about laptops there's a sweet new one (I think by toshiba) with a turnable screen that can become a sort of big PDA :)
yeah i guess those are the new ones on which you can write with a pen, but i heard they are pretty expensive.

Thanks thomas and bitrake for clearing out my confusion with refresh rates :)
Posted on 2003-02-15 00:58:13 by clippy
this is just out of curiosity, but how exactly does a lcd display work.
Why is it called Liquid Crystal Display?

Also why is it that in a LCD display if you look at it from different angles then certain areas of the screen either appear faded or dont appear at all while in a TFT display it appears fine from all angles?
Posted on 2003-02-15 06:11:52 by clippy

yeah i guess those are the new ones on which you can write with a pen, but i heard they are pretty expensive.

Thanks thomas and bitrake for clearing out my confusion with refresh rates :)


what, tablet computers? fun :) i just have a tablet + a computer, but still very fun!

LCDs are based on the fact that some substances have two freezing points. not exactly sure how colour LCDs work.
Posted on 2003-02-15 07:22:58 by jademtech
Originally posted by gladiator
this is just out of curiosity, but how exactly does a lcd display work.
Why is it called Liquid Crystal Display?


Here's a nice article about it:
http://electronics.howstuffworks.com/lcd.htm

Also why is it that in a LCD display if you look at it from different angles then certain areas of the screen either appear faded or dont appear at all while in a TFT display it appears fine from all angles?


They don't appear fine from all angles. A TFT display *is* an LCD. LCD stands for liquid crystal display, TFT stands for thin film transistors. TFT is just the technique used for active-matrix LCDs, not a totally different type of display. However LCDs using this technique are often called TFT displays..
An LCD works with two polarizing filters and a liquid crystal layer in between. Such a polarizing filter makes the lightwaves pass only in one direction. The second filter is rotated 90 degrees so that no light passes when both filters are used (the first one only allows the light in one direction, the second one only at a different direction so no light will come through). However the crystal layer will change the direction of the light that passes by a certain degree, depending on how much current is put on it. This way the amount of light that finally comes out can be regulated. It's because of the polarized light (= light in one direction only) that you can't see the image from all angles.

Thomas
Posted on 2003-02-15 08:47:22 by Thomas
btw if i look at my lcd from the botom. every thing looks inverted!
Posted on 2003-02-15 17:54:37 by Qages
But what about TFT televisions?

In a television the image is always changing so there is no such 'infinite' refresh rate ever, so why is a TFT television said to be better?
Posted on 2003-03-11 02:39:36 by clippy
No, TFT TVs have the same 'infinite' refesh rate. You need to distinuish between the refresh rate of screen (i.e the number of times it draws a full image per second), and the rate at which the data appears (FPS of a game or movie). The former is just how many times the sceen is painted. With CRTs, an electronic beam has to lit the pixels and that is done at a certain speed. This speed determines the refresh rate. As I explained, lower refresh rates lead to flicker, since pixels are not lit frequently enough. The latter is just at what speed a game, movie or whatever feeds a frame to the screen. Even if this happens at 10fps, on a monitor with a refresh rate of 120, the screen doesn't look flickery but of course the movie will play very slow (like slow motion in steps).
On TFTs, the first refresh rate doesn't exists. TFT pixels aren't continuously redrawn, they are just on or off (or slighty on etc.). If at one point the TFTs puts a pixel on, it won't dim or change until the next color change. Therefore it doesn't have to be refreshed to stay on.
But while there is no pixel refresh rate for TFTs, there is a response time. The response time is the time it takes for a pixel to change (I explained this earlier). If this time is high, movies etc appear sloppy and you get things like ghosting, frames appear to blend with previous frames because the screen couldn't change its image fast enough. If you divide 1 by this response time in seconds, you get a sort of refresh rate, but this is a totally different one than with CRTs. It only says how often per second the screen is able to change, but *not* how many times it can refresh it, since TFTs don't need to be refreshed.

Thomas
Posted on 2003-03-11 03:24:28 by Thomas
Thanks thomas, i finally seem to get it now.

I was looking at howstuffworks.com and electronics seem pretty interesting.

Btw,
Can hardware be made at home like software?
Posted on 2003-03-14 00:40:55 by clippy