The Other Side of the Screen

Laptops, Smartphones, Car dash-boards, Audio systems, Cameras, Washing machines, Televisions or be it any other electronics device, every single of these items has a face and that face allows us to receive and deliver instructions to these devices. Screens are the thing that attach so to say ‘face value’ to these objects. They are everywhere, in fact you are staring at one right now and a honest fact is that you can not work without them! Until and unless you want to spend the whole day meditating in a cage! But have you ever wondered what goes on inside these glowing rectangles? Have you ever brought a magnet closer to screen and see what happens? (Try this at your own risk). How does over exposure to the screen light affects our visual system? In this blog post we will try to find answers of these questions.

Evolution of screens
From bulky CRT displays to sleek LEDs screens have come a long way

So without wasting any time Let’s talk about “The Other Side of the Screen”. Here we will be specifically talking about the mechanisms of a LCD/LED screen however, I must say that there are other type of screens as well.

You’ve probably heard of the term Resolution, it is nothing but a total count of Pixels which are distributed horizontally and vertically, essentially covering the whole of screen. But what are Pixels?

screen
Magnified image of a screen, one small glowing dot is called a Pixel

Pixels

Pixels (which literally means Picture Elements) can be understood as analogous to cells on your skin, they are the basic unit of any screen. Each pixel can be divided into three Sub-Pixels of Red, Green and Blue color. By changing the intensity of each color light each pixel can have its own unique color (We already know that our brain blends different color to obtain newer shades of color). The mechanism by which this is done is described later.

pixel-2
See! each Pixel is made up of three Sub-Pixels

A Game of Light & Shadows 

The idea of a screen is very similar to the game of light and shadows that everyone of us used to play during our childhood. The game had three important things to look for:

  1. A light source: Could be lamp, torch or even fire.
  2. An object to block light: Your hands most of the times do this.
  3. A flat surface: Where the light which is not blocked falls and makes a negative image of the object.
Shadows
Hands block the light creating a shadow of the object on the wall

Analogous to the above explained order the LCD screen also has three layers:

  1. Bottom layer to work as Light source : Its function is to supply light so it has a light source, in LCD screen CCFL (Cold-Cathode fluorescent Lamp) is used.
  2. Middle Layer to control the intensity of light: It has all the magic that we need and is explained below.
  3. Upper layer of flat glass: It is simply the screen on which the light polarized and adjusted by the sandwiched layer falls onto.

Let’s try to understand that what goes on inside the Middle Layer, This layer is made up of four layers:

  1. Color Filter: Specific filters are arranged to allow only Red, Green and Blue light in one Sub-Pixel.
  2. Horizontal Polarizer: Don’t worry if you don’t know what a Polarizer is, it is simply a filter that limits the light wave in one particular direction, so naturally horizontal polarizer will limit the light in horizontal direction.polarization of light
  3. The Middle Layer: It is filled with liquid having special kind of rod like molecules called ‘Nematic Molecules’. They perform a very special task of rotating the direction of light from 0 to 90 degrees depending of their own arrangement which is sensitive to the electrical field applied. So when the voltage is applied to the maximum, the rod shaped molecules assumes the shape of a twisted helix like structure which rotates the light by 90 degrees. If we weaken the applied voltage which results in weakening of electric field the molecules reduce their angle of rotation and as usual the output light rotation is reduced. When no voltage is applied the light passes through without any rotation.

    Nematic molecules
    Nematic Molecules are responsible for rotation of light
  4. The Vertical Polarizer: This is final screen which only allows the vertical component of the electric vector of light to pass. Hence the 90 degree rotated light will cross through without any intensity change whereas only the vertical component will cross in case angle of rotation less than 90 degrees. For 0 degree rotation no light will pass by.

Too much to process? Let’s Recap, A colored horizontal light coming out of a polarizer is rotated to different extent depending of the voltage applied. Another vertical polarizer only allows the vertical component of the rotated light to cross thus resulting in intensity change of the colored light.

Voltage maximum = Maximum intensity of output light = Maximum Red/Green/Blue color

Voltage minimum = Zero intensity of output light = Black color

Now, if you are still with me, we have done all the hard work and its time for the final touches. Corresponding to each pixel there is a transistor attached which individually regulates the voltage applied to each pixel so that it gives off the required color. There are literally thousands of transistors working on your screen right now so that each Pixel can participate their own bit in the entire image formation.

Looking at the bigger picture

Our brain has this incredible capacity of finding patterns everywhere by rearranging the received information in an intelligent manner. So even if some of the pixels are not working properly, our brain will neglect that redundant information and forms a meaningful image with the visual information received from other pixels.

71e527449c5ec87969d5c2b66c96a7a6
Take a closer look and then look from a distance, Did you see anything interesting? 

Now I’ll leave you to ponder over the effect of magnets with screens and the adverse affects of over exposure to screen light. In future I will try to explain them in a separate blog post so stay tuned and Thanks! for the read.

BIBLIOGRAPHY:

  1. https://www.youtube.com/watch?v=0B79dGR19Tg
  2. http://electronics.howstuffworks.com/lcd1.htm
  3. https://www.youtube.com/watch?v=k7xGQKpQAWw
  4. http://www.digitaltrends.com/home-theater/led-vs-lcd-tvs/
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