TV Purchase Guide – Display Technology : LED
Following up the previous articles that there were about choosing the correct display technology that can meet your needs. Since now, we have talked about CRT (Cathode-Ray tube) and LCD (Liquid Crystal Display).
In this article we will explain LED display technology but in order to understand LED displays better we should review the LCD technology.
The reason is that they operate similar to each other. As it was mentioned, LCDs use two light filters to polarize the light and as these filters are perpendicular to each other, the light cannot be displayed on the screen.
If you want to experience the aforementioned effect you can simply experience it with two sun glasses.
As sun glasses use the polarization effect to filter the sun light in order to protect our eyes against the ultraviolet waves, if you see the light passing through one sun glasses, the light would be darker than natural light.
Now try to position the second sun glasses parallel with the first one that the light can pass through both of them. Now the light would be even darker than the previous step.
Now we come to the most interesting part of our experiment. Now we should rotate 90 degrees the second sun glasses and position it perpendicular to the first one. You will see that in this situation you cannot see anything and the light will be blocked with these two perpendicular filters (sun glasses).
This is exactly what happens in LCD and LED displays. That is two light filters are placed perpendicular to each other a liquid crystal is located between these two filters. The role of the liquid crystal is to rotate all of the light or a portion of the light according to the applied electric filed.
Till now, the procedure of generating pictures are similar between LCD and LED and it was the reason we explain in another way how these types of displays work. But, now we should explain the difference between these two models.
The main difference that makes a big difference between LCD and LED displays is the type of backlight being used. Actually as it was mentioned before, LED is a type of LCD with a different type of backlight. LCDs use CCFL which is stands for cold-cathode fluorescent lamp to emit the light to the liquid crystal layer. But, LED displays use LEDs to generate light. LED stands for light emitting diodes that they as a semiconductors have some benefits which make them very popular these days.
Not only this, LEDs are much more efficient and that is the reason they are now being used in many applications because of their energy efficiency.
Because of the characteristic of LEDs, they can emit light that can have higher contrast which makes it possible to use these types of displays in open door situation or in sun light.
In some type of LED displays, there is no liquid crystal display and the LEDs themselves create pictures of the screen and it can be done with RGB (Red Green Blue) colors . That is, each pixel contains these 3 colors and each color is generated by an LED.
Now we can understand why it is said that LED displays can display better dark color or has a better contrast. To understand this difference, we should consider how black color is generated in both LCD and LED displays.
In LCD displays, the color black is would be shown on screen, when all the lights are blocked by the filters which means when no electric field is applied to the liquid crystal. Therefore, there is actually light there, but it is tried to be blocked by the filters. And it is the reason that in LCD, the blacks are not completely black and they seem like to be dark blue.