All sorts of computer’s primary medium of outputting some result is some form of display. Even in a tiny calculator has display. This term display here is wide not limited to LCD rather all of the different kind of output device such monitors, projector, VR headsets, falls under the category of display technology. All sorts of display technologies have some form of display adapter, video card that act as a communication medium between CPU and display.
Almost every computer out there today uses the Liquid Crystal Display (LCD) technology as the primary output device for the computation. This LCD varies in terms of size, weight, type etc. We are all so familiar with the LCD display, but how does it work?
In order to understand the geeky concept behind how LCD works, you need to understand the polarity of light. Anyone who has played around with a prism, found the reason behind the visible rainbow, should know that light travels in waves and wavelength of the light is then determines the colour. One of the most interesting facts here is the light emanates in three dimensions from its source. This wavelength varies a lot if terms of speed to you. When we see a white light, we are seeing multiple wavelength of light coming to us simultaneously, if we see one colour, that is one wavelength.
Polarisation and liquid crystals
Typically, the wave coming out from light source come in as, imagine, shooting numerous laser at different angle, different place and it is a mess. When you put a polarised filter between you and the source, unnecessary light orientation gets eliminated and come in only the waves of similar orientations. You would still see all of the colours but makes the image darker. This is why lot of sunglasses have polarised filter.
Liquid crystals has the same concept of polarisation. Liquid crystals are the product of formulated liquid full of long, thing crystals which always tend to move in the same direction. This substance basically acts as a liquid polarised filter. If you had poured this stuff between two layer of glasses, you would get an advanced pair of sunglasses. Don’t try though.
If you had one of the sheets of glass cut in neatly nice grooves on one side of the sheet of glass, and you placed the liquid, the molecules would naturally line up along the grooves of the surface. Now if you place another of fine sheets of grooved surface but placed at a 90-degree orientation to the other surface, exactly opposite to the first sheet, the molecules in between would begin to line up in a twist.
Placing two perpendicular polarising filters are then placed on either side of these crystals, they will twist the light and enable to pass. Now if you expose these liquid crystals to any electrical medium, the crystals will change their direction to the flow of the electrical field. Now the twist will be gone and no light passes through.
A colour LCD screen is made up of numerous number of tiny liquid crystal molecules called sub-pixels and are arrange in rows and columns between polarizing filters.
A translucent sheet above each of the sub-pixels is coloured in red, green and blue. This is where the classic RGB comes in. Each of this three tiny sub-pixels – red, green and blue forms a physical pixel. Now that all the pixels are laid out, all they need is the right charge at right place to form such images and so on.
Static charging and passive matrix
The early displays used something called static charging to render the display contents with shapes and elements. But this would not work on a PC. So, early LCD screens used a something like a matrix of wires. The concept went like, they had vertical/Y wires which ran across every sub pixel in the column and the horizontal/X wires ran along the row of sub pixels. Charge on both of the X and Y wires with enough voltage would light up a single sub-pixel.
So, if you needed a colour you needed to have three matrices. They intersected adjacent to each other so closely. Right above the intersections, the glass was covered with tiny dots of RGB. The amount of voltage on the wires created a different levels of RGB, eventually rendering different colours. This technology was called passive matrix.
Thin film transistor
But the current form of LCD monitors uses which is called thin film transistor (TFT) or an active matrix technology. This refined the X and Y wires and one or more tiny transistors control each of the colour dot which in result, renders the faster, crisp, tighter colour pictures than earlier technologies was able to provide.
So, an active matrix display provides two polariser on each side, then the layer of thin film transistors and then the liquid crystals in between. So, this is the secret of how LCD monitor works on the cellular level.