A Laptop monitor appears like a film negative when seen from the side. Why?

The sleek screens of the Laptops are based upon the liquid crystal display technology. We have studied above that the LCD monitors rely on fluorescent backlights behind the LCD panel to provide the illumination that creates the image. We should also be aware that LCD displays utilize 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.

Here we must note that the liquid crystals work like shutters that either block the backlight or let is pass through. These make hundreds of thousands of pixels that are charged or not charged, making them reflect or not reflect light to form images. When we see the screen from 180°, it would mean that the pixels are fully visible. But viewing from sides, LCDs may appear to lose some brightness and image quality.

The concepts which play important role here are the Passive matrix addressing and Active matrix addressing. The earlier LCDs used the passive matrix addressing, which means that only m + n control signals are required to address a m × n display. A pixel in a passive matrix must maintain its state without active driving circuitry until it can be refreshed again. But in the Active matrix addressing, each pixel is attached to a switch-device, which actively maintains the pixel state while other pixels are being addressed, which also prevents crosstalk from inadvertently changing the state of an unaddressed pixel. The best example is Thin Film Transistors (TFT).

But the Passive matrix addressing has grown older and today the black-and-white palmtops, pagers, and mobile phones use passive-matrix LCDs. However, the TFT Monitors and latest LCD screens use the Active matrix addressing that lets us view the screen from all angles with superior image quality.

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