LCD monitors
Photo: G.R.N. Somashekar
QUESTION: Why does the laptop monitor appear like a film negative when seen from the side?
I. Sivakumar, Sivakasi, Tamil Nadu
ANSWER: Sleek screens based on liquid crystal display technology are increasingly popular as default display on laptops. LCD type monitors are based on a newer technology and they have great space and energy saving advantages over CRT monitors. LCD monitors rely on fluorescent backlights behind the LCD panel to provide the illumination that creates the image.
LCD displays utilise two sheets of polarizing material with a liquid crystal solution between them. An electric current passed through the liquid causes the crystals to align so that light cannot pass through them.
The liquid crystal acts like a shutter that either blocks the backlight or lets it pass through to light up a particular colour filter. The screen has hundreds of thousands of pixels that are charged or not charged, making them reflect or not reflect light to form images. One of the main disadvantages of LCDs when compared to CRTs is their limited viewing angle.
A theoretical viewing angle of 180 degrees would mean that it is fully visible from any angle in front of the screen. Because of the way light passes through the liquid crystals in the display, LCDs may appear to lose some brightness and image quality as you move to the side of the screen, or above or below it.
The origin of this problem lies in the use of bire fringent materials where the polarisation of the propagating light is very critical. This problem exists in Passive matrix LCD screens.
This is the older technology and is less popular these days. Today, most black-and-white palmtops, pagers, and mobile phones use passive-matrix LCDs.
Active matrix LCD screen allows you to view your screen from all angles with superior image quality. The most common form of active matrix screen is TFT (Thin Film Transfer).
Nearly all-modern colour LCDs — both in notebooks and for desktop monitors — use a thin-film transistor, to activate each cell/pixel. They can be viewed at any angle.
K. Kamalakkannan, Doha, Qatar
Printer friendly
page
Send this article to Friends by
E-Mail
Sci Tech
