Different types of smartphone touchscreen displays - their pros and cons
There are many different kinds of displays used on mobile phones these days with different manufacturers offering alternative display technologies on their handsets.
Manufacturers often claim that their technology is ‘the best’ and that it is ‘revolutionary’ but as you’ll see in this blog many of the displays have their own pros and cons.
Why is it important to me? Does it really matter?
It’s very important as you’ll spend pretty much all of your time looking at the screen when interacting with your handset of choice. It’s down to this fact that the display aspect of the handset market is particularly diverse.
We’re going to give you a rundown of the seven main types of screen tech used in today’s smartphones starting with:
TFT LCD (Thin Film Transistor Liquid Crystal Display)
TFT LCD is a variant of the standard LCD (Liquid Crystal Display), TFT LCD uses thin film transistors and runs as an active matrix LCD. This means that every pixel is connected to a capacitor or transistor which can control the state of the pixel.
Pixels are the smallest controllable element of a picture and they are arranged in a two dimensional grid on a flat plane. In today’s market most LCD displays are TFT LCD – they are the most common mobile phone displays used and are often referred to as ‘LCD displays’ rather than TFT LCD, so when you see a mobile handset, TV or PC monitor that states it has an LCD display you’ll know that it is really a TFT LCD.
The science behind the displays is pretty neat, even though they are (technologically) one of the simplest forms of display they are still surprisingly complex as shown in the following video.
As the video explains, light is filtered through a polarising filter and is then ‘twisted’ to fit through another filter – this happens once the pixels are twisted at 90 degrees (or to match the second polarising plane). The twist can be switched on and off depending on whether or not a voltage is applied to the liquid crystal display.
This activation and twisting of liquid crystals is known as the Twisted Nematic (TN) effect. It is this effect that forms the difference between Conventional Twisted Nematic and IPS-LCD as outlined with our next display type.
The TN display will have very fast refresh rates and a good response time which will result in less ‘ghosting’ of images, however TN displays suffer from extremely limited viewing angles, especially in the vertical direction. When viewed from the side colours will shift when viewed off-perpendicular and in the vertical direction, colours will shift so much that they will invert past a certain angle.
IPS stands for ‘In-plane switching and is considered to be the offspring of the TFT LCD. An IPS-LCD display will have a higher quality resolution and wider viewing angles when compared with a TFT display.
Where the TFT LCD display features a single capacitor per pixel, the IPS-LCD has two capacitors per pixel.
Due to the increased load based on the larger number of capacitors, a stronger backlight is then needed – this will increase power draw but results in increased viewing angles and more accurate colour representation.
The technical difference between an IPS-LCD and a TFT LCD is as follows, a TFT LCD relies on an effect called Twisted Nematics, each ‘Liquid Crystal’ will be rotated so that it lies perpendicular to a polarising filter. This happens when a voltage is passed through the length of the area between polarising filters as shown in the image below.
In-phase switching differs in that, instead of passing the voltage or ‘electrical field along all liquid crystals, an electrical field is passed through each end of the liquid crystals individually – this is called a ‘lateral electric field’.
The lateral electric field keeps the liquid crystals running parallel to the electrode pair and in turn the glass substrate of the screen.
The pros of using an IPS-LCD display are that the colour representation will be a lot better and the viewing angles are increased substantially over a TFT LCD, however there will be a larger power draw so battery life and power consumption can be issues if IPS screens are employed on devices like notebook computers plus IPS displays have a longer response time than TN panels.
Super LCD (SLCD)
Super LCD is a further enhancement of LCD technology. Super LCD displays (unlike LCD) have no air gap between the outer glass and inner display - this helps to reduce the amount of reflected light, perfect for increasing visibility when used outdoors due to less glare coming off the screen.
As there is no air gap between the outer glass and inner display the images on screen can appear to be closer to the user with images appearing to be on the glass screen rather than sunken into the handset. This helps to give SLCD displays excellent viewing angles with no loss of colour representation of brightness.
Another bonus is that these displays use less power than a ‘traditional’ LCD screen, plus SLCD displays can give you great screen brightness as you can always install a more powerful backlight.
There is one disadvantage behind this however as the backlight in an LCD display is always turned on - this can lead to improper ‘Blacks’ on screen. The contrast ratios (when compared to AMOLED) can also be effected as the screen brightness suffers when you increase colour saturation, these issues have been eliminated though with improved IPS display advancements.
Over the last few years handset manufacturers have started returning to the use of SLCD screen over AMOLED mainly due to the expense and lack of production capacity of AMOLED displays.
Handset manufacturers like HTC mostly use SLCD displays on their handsets and have chosen to use Super LCD3 with one of their latest handsets the HTC One (M8).
AMOLED (Active-Matrix Organic Light-Emitting Diode)
AMOLED display technology has been used in mobile phones, digital cameras and media players since 2010 but really only became mainstream around 2012. There are also certain manufacturers who have started using OLED technology in TVs.
Many smartphone manufacturers have decided to use AMOLED at some point but Samsung have used this display type almost exclusively for the last few years, so much so that ‘SAMOLED or Super AMOLED’ has been a term used for any AMOLED display used on a Samsung handset (more on Super AMOLED later).
A quick explanation on what an Active-matrix Organic Light-emitting diode is should be in order – whatever it is it certainly sounds impressive!
An ‘Active-Matrix’ is a type of ‘addressing scheme’ that is used in flat panel displays. With this style of addressing scheme each pixel is actively maintained by an attached capacitor or transistor that govern the pixel state while other pixels are being addressed.
The OLED part describes the use of a specific type of thin-film-display technology in which an emissive electroluminescent film made of organic compounds is activated in response to an electric current.
AMOLED displays operate without a backlight so can give you deeper, richer Blacks than other display models. The Blacks that you see when looking at an AMOLED screen are really just the scree when it is turned off. An AMOLED display doesn’t need to ‘light up’ the pixels to display Blacks, they can just choose to not switch on the pixels where Blacks are required.
Due to the fact that AMOLED displays do not use backlights and when displaying Blacks the pixels receive no power these types of screen have fantastic power consumption which helps with battery life.
So despite the fact that some manufacturers are returning to SLCD displays due to lack of production capacity and expenses of AMOLED displays have better power consumption and viewing angles when compared with TFT LCD.
This brings us up to the latest iteration of OLED displays; the Full HD Super AMOLED display which is the latest iteration of the OLED display series.
This type of screen uses a new pixel arrangement called the “Diamond Pixel” arrangement – it has a Full HD resolution of 1920 x 180 with 441ppi, it also delivers the best colour gamut with 97 per cent of the Adobe RGB colour space, which is impressive!
The Full HD Super AMOLED display is currently used on great handsets like the Samsung Galaxy Note 3 and Galaxy S4.
Anyone who has used or seen an Apple product manufactured after June 24th 2010 will be familiar with the Retina display. Originally released on the iPhone 4 the Retina Display has been used on nearly every Apple device since.
Retina displays are so called as there is a bit of science wizardry taking place with the screens that relates to the way an eye perceived pixels at differing distances.
These displays have so high a pixel density that within a certain distance the human eye cannot resolve the individual pixels. In layman’s terms, the correct ppi (pixels per inch) for a particular screen size will result in displays that appear to be pixilation free when viewed at the correct distance.
Apple have placed a lot of faith in user interaction with this technology, for instance a mobile phone when held in the hand is probably held closer to the face than an iPad - which would probably be held away at a further distance.
So, according to Apple smaller devices would have 326ppi, midsized devices like the iPad Mini would have 264ppi and larger devices like iPads and 13” Macbooks would have 220ppi. There is a correlation between screen size, distance and ppi.
It really is rather clever of Apple to think this way, a lot of thought has been put into how users interact with their devices and only Apple would really have created that link between screen size and user distance from said screen. While it seems obvious to us when spelt out Apple got there on their own and this goes to show why the company is still innovating and creating great hardware.
Nokia Clear Black Display
The Finnish communications and information technology company situated in Helsinki is quite possibly one of the best known names in the mobile world.
Founded in 1871 when company founder Fredrik Idestam built a ground wood pulp mill on the banks of the river Nokianvirta next to the town of Nokia.
Fredrik was joined by his close friend and statesman Leo Mechelin around the same time and turned his firm into a shares company.
Over the course of the next 100 years, Nokia continued to revolutionise various industries around the world ranging from electricity generation, rubber products, footwear, cable works and then in 1960 the electronics section of the cable division was founded and the production of its first electronic devices began in 1962
That’s enough of the history lesson about Nokia (who knew about all of that?), needless to say that Nokia started dealing with mobile handsets and have invented quite a few iconic handsets since they started (Nokia 3310 anyone?) and then a few ‘alternative’ handsets like the Nokia N-Gage and Nokia 7280 alternatively known as the ‘lipstick phone’.
Continuing on with the theme of Nokia’s innovations we’re finally onto their prized screen tech the ‘Nokia Clear Black Display’. This display type minimises the amount of reflected light coming from your handsets screen by utilising polarising filters.
Polarising is the action of restricting light waves in a particular plane of space, it can also be seen as allowing certain light waves entrance through a slit with only the waves that are properly aligned with the opening being able to pass through.
br /> If you angle two polarising filters at 90 degrees to each other no light will be able to pass through the second filter (sounds vaguely similar to the Twisted Nematic (TN) effect mentioned above right?).
This method of ‘filtering’ is what forms the basis of Nokia’s Clear Black display, by eliminating the amount of light that bounces back off the screen you improve the quality of visibility and also gain darker Blacks in the process.
Enhanced outdoor visibility is the major plus to using Clear Black displays, by using multiple polarisation layers to eliminate reflections you don’t need to pump up the screen brightness when outdoors to compensate for glare which will help to save on power consumption which in turn helps to save battery life.
Nokia have used the Clear Black displays on their popular Lumia range of handsets and it appears that they will continue to use this display type for a long time or until they can invent something better to use.
To finish with
We’ve covered pretty much every screen type that is being used in the mainstream market today from AMOLED to TFT LCD and everything in-between. The mobile handset market moves along so rapidly with new technologies being found and released perhaps every 6 months or so, however screen technology has remained rather stable over the last few years with no real leaps forwards in terms of outstanding new ways to manufacture a display.
Who knows, perhaps in the next few years we’ll see another jump forward in the way in which we interact with our mobile and handheld devices but until then as far as current limitations go is one type of screen better than the other?
We’d be inclined to say no – it all comes down to the end users and their needs, after all they are the ones who are looking at the display and know their likes and dislikes. One user may require a super sharp screen with great viewing angles while another may need a display that looks great when viewed in direct sunlight.
One thing we do know for sure however is that there has never been a more diverse mobile market than there is right now with something out there to suit everyone, be it a slick intelligent smartphone or a rugged rough-and-ready tough phone.