Why are we still using LCD screens?
I don’t own that many phones but I happen to own one with a higher than average historical significance. The first mobile phone with an AMOLED Display, the Samsung Omnia II GT-I8000.
Back then this was a huge deal because It was a unique feature, no other phone had an OLED display. This was also before the time of all these “super” LCD technologies and LCD screens had problems such as low contrast ratio bad color reproduction and view angle dependence. Suddenly OLED screens seemed to be the way of the future with its infinite contrast ratio and simply the raw coolness of being a totally new technology.
Today it doesn’t seem that way anymore, this phone looks kind of outdated because of it is thick and has a relatively small screen area. But most importantly, why is LCD still here? It’s like one of those failed promises from science fiction movies, where are the flying cars?
Color LCD displays, even though thinner than CRT displays, are in fact very sophisticated and complex in design and the way they work. The way I’d like to put it is that they are so cleverly designed they are just stupid. To illustrate this, we have to talk about how LCDs work, of course you can find this anywhere on the internet, and you probably already know this. but just in case, here is a simple explanation:
An LCD panel works by selectively blocking out parts of light coming from its back light by using the fact that light could be polarized. The first layer polarizes light, which in this case basically means only light waves going in a vertical direction could pass this filter, this eliminates about 50% of the back light. And then light has to be colored by passing though a color filter, this also eliminates a large amount of the back light because only light of specific wavelengths could pass through these filters. Light then goes through the Liquid Crystal layer which can be controlled to rotate the light into a horizontal polarization such that it could pass through the last polarization filter. This is a very long process and eliminates a lot of the back light as waste, especially when displaying full black, which is when almost all back light is blocked and wasted.
When you think about it. It is really astonishing how far we have come in perfecting such a complicated way of blocking out light. The image quality provided by modern LCD panels can only be described as magical. For example, if you want your color filter to provide deep and rich prime colors, they would have to be less efficient by only allowing a very narrow range of wavelengths of light to pass through , and then your screen would be too dim. But if you allow more light to pass through, then your colors would be inaccurate or less saturated. This is why early LCD displays have very weak colors. Yet despite all these, smartphones today give us all these life like colors while having great battery life, all in these sleek and thin bodies.
In comparison, OLED screens are much much simpler. It’s just a glowing sheet! Of course there has to be electronics and things to make it all work but the same is true just for the liquid crystal layer in LCD displays.
Diagram of a pixel on an OLED display!
The question is, if OLEDs are so great, why are we still using LCDs? Other than the well-known reasons such as cost and production volume, there are a few more. Namely, performance.
So how could the great high-tech OLED display have bad performance? Aren’t they supposed to have infinite contrast ratio and more saturated colors? The first problem that plagued the very first generation of AMOLED displays is blue sub-pixel. Since OLED screen is just a layer of glowing material, different materials are used to produce each of the prime colors. The problem was that the blue ones will loose output luminance over time, they have a shorter lifespan than the other colors. To solve this problem, early AMOLED screen used a different sub-pixel structure, different from the otherwise universal RGB. It is the infamous Pentile RGBG structure. What it is is that instead of three sub-pixels per pixel, it has just two, but alternates between blue+green and red+green. This way blue pixels (and red) could be made significantly larger enabling them to last longer, also green is chosen to repeat more because we are more sensitive to green and makes the image appear more detailed than if they had picked red. So in a way, these displays have a fake resolution because each of its pixels could not stand on its own, for they lack one of the prime colors. The Samsung Galaxy S III for example despite being advertized as having a 720×1280 resolution, only has 67% the number of sub-pixels as other 720p LCD phones for this exact reason.
The second problem is that these displays have too much saturation. This is like a double edged sword type of thing, with great power comes great responsibility. Samsung decided that they were going to use this as a marketing gimmick and make their phones “pop out” when compared to others. But in fact, you don’t want your display to over saturate because there is a standard in color reproduction (sRGB) and whoever created the contents, an artist for example, have decided that their work is the best at whatever saturation within this standard. If your screen displays everything as more saturated than they should be, you are not looking at that content the way its creator meant it. Obviously the ideal solution would be to have the capability of showing very saturated colors, but also show contents as they were meant to be shown. Unfortunately that is currently beyond the way our mobile operating systems work. There is one benefit to this however, because OLED screens uses less power when displaying a saturated color, versus an unsaturated color, white being the extreme example using the most amount of power.
The third problem is efficiency. You would think that OLEDs would be more efficient since it doesn’t have all those wasted back light found in LCD displays. But at this point, there really isn’t much of a difference. In fact OLED screens can be less efficient depending on how much white do you use on your phone. This is simply because of the low electricity to light conversion efficiency of current OLED technologies. This has improved a lot since the Samsung Omnia II and I’m sure one day it will surpass LCDs even when displaying full white. Currently, due to this problem, OLED screens are also significantly dimmer than LCD screens because making them too bright will drain the battery, as well as age the blue pixels even faster.
There are also other problems, such as reflectance and pixel density, but overall what we have seen is a comeback of LCDs since the introduction of iPhone 4 I would say.
When OLED displays were first introduced, despite its problems I have mentioned above, I think it was still superior to all other LCD displays just because their contrast ratio and color saturation were unacceptably low. But since the introduction of iPhone 4, LCD has caught up with all sorts of new and old tricks. Today mobile LCD screen have between 1,000 to 1,500 contrast ratio which is very good and black doesn’t leak any light unless viewing in totally dark rooms, making infinite contrast ratio displays kind of pointless. Mobile LCD displays also cover and even surpassed the full range of colors defined in the sRGB standard, which renders the high saturation of OLED displays unnecessary.
But when it comes to the future of display technology, I have no doubt that LCD will have to give up its place to self-illuminating surface technologies such as OLED. It has the potential to be everything LCD is today, but thinner, lighter, more efficient, more reliable and coolest of all, flexible and transparent.