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In 2007, Steve Jobs introduced the original iPhone.
One of the most innovative and revolutionary products of the 21st century, ushering a new
era of smartphones, and waiting in line to get one.
The furore for this new phone was due, in large part, to the LCD multi-touch panel that
allowed you to see and interact with the device with a clarity and mobility never seen before.
Apple wasn’t the first to introduce touch panel LCDs into cell phones, but they were
first to make people care about it, they revolutionised what was once a clunky and frustrating technology,
to one that could be used easily for typing on screen and gesture control.
The screen itself featured a 3.5” diagonal 320x480 resolution LCD.
Most major shifts in iPhone usability and design over the years have been around the
display, from the iPhone to the iPhone 3GS the phones had a display density of 163 pixels
per inch.
The iPhone 4 “retina” display doubled that to 326 PPI, halving the size each pixel.
This pixel size remained constant for another 7 years, while generational progress was made
in LCD technology.
More consistent backlighting, consistent colour and brightness when viewing off angle, and
a wider colour gamut gave the new iPhone 8 the gold standard LCD panel.
But for the iPhone X, Apple is taking a sudden departure from its faithful LCD screens, and
jumping in bed with their arch-rival, Samsung, who are manufacturing it’s new OLED display.
The Apple watch used OLED, but Samsung has been utilizing and maturing OLED technology
for years in their Galaxy smartphones.
This is the first time most Apple enthusiasts will experience OLED technology.
So, what are the fundamental differences between LCD and OLED?
LCD stands for liquid crystal display.
The liquid crystals used, fall somewhere in between a liquid and a solid, which allows
them to change their molecular orientation when an electrical current is applied.
This is incredibly useful,as it allows us to use the molecules to manipulate light that
is passing through the liquid crystal.
Liquid crystal pixels do not produce their own light, and so require a backlight to provide
the displays lighting.
In the past, cold cathode fluorescent lamps (CCLF) were used, but in modern LCD panels
LED backlighting is used with a backlight uniformity filter added to ensure even lighting
across the panel.
Next the light passes through a polarization film which only lets light traveling in the
horizontal orientation to pass through, followed by the liquid crystal group and then another
polarizing filter oriented 90 degrees to the first.
If you are familiar with polarizing filters, you will know that light cannot pass through
two filters when they are aligned perpendicular to each other.
So, light depends on this liquid crystal layer to orientate the light to allow it to pass
through the second filter.
The liquid crystal layer is sandwiched between two electrodes and two pieces of etched glass,
forcing the liquid crystal molecules into a near predictable 90 degree twist.
When a voltage is applied through the electrodes, the crystal molecules begin to realign in
the direction of the current, a larger voltage will result in full 90 degree twist.
As light passes through, it will follow the direction of the crystal molecules before
encountering the second polarization filter.
So the liquid crystal layer essentially acts as a controllable light valve.
If light is allowed to pass it will travel through a coloured filter, giving it one of
three colours.
Red, blue or green.
This structure is called a subpixel.
Combine three sub-pixels with red green and blue filters and you have a single traditional
RGB liquid crystal pixel.
This brings up a few really interesting characteristics of LCDs.
The first is that even when the panel is displaying a black image, the backlight is always on,
causing a large battery drain and some light leakage at pixel boundaries and the edges
of the screen, which negatively affects the screen contrast ratio.
With the iPhone X, Apple engineers have adopted a fundamentally new display technology, OLED
or organic light emitting diodes.
Samsung have a near perfect monopoly on the manufacturing market for these screens, manufacturing
90% of the world’s supply and holding the majority of the world’s patents [1].
Forcing competitors like Apple, to purchase from them to remain up to date with the best
technology on the market, although it hasn't stopped them from reportedly investing billions
in Samsung's major competitor, LG Display [2].
OLED works very differently than LCD in a few key ways.
For starters, there is no backlight.
Instead, each pixel is self illuminating through the light emitting process called electrophosphorescence.
There are two organic compounds called the emissive and conductive layers that are sandwiched
between an anode and a cathode.
As an electrical current flows from the cathode to the anode, electrons are given to the emissive
layer, and removed from the conductive layer.
The electrons in the emissive layer now migrate to fill the holes in the conductive layer.
When they do, extra energy is released as a photon.
This entire process is controlled and structured by the TFT matrix, and the structure is placed
on a substrate of either glass or polymer.
Since there is no backlight and each individual pixel is individually controlled, substantial
power saving can occur when displaying dark or black images.
In addition, OLED panels are significantly thinner and lighter than their LCD counterparts,
allowing for slimmer devices with razor sharp bezels and flexible screens, like the one
in the Samsung Galaxy S8.
Lastly, OLED panels have high brightness and true zero pixel values, leading to insane
contrast ratios of over 1,000,000:1.
Blacks are inky, colors are more vibrant, and localized brightness can be greatly improved.
There are some growing pains with OLED technology holding it back in the mainstream consumer
market.
The chief limiting factor is burn in.
Burn in occurs when the organic layers of the pixel begin to breakdown from prolonged
usage.
As the layers decay, they can become significantly less bright than the pixels around them, which
can make stationary UI elements appear as a ghost image.
This mainly occurs from prolonged static images, such as user interface icons and is the single
largest reasons OLED computer monitors or TVs are not yet mainstream.
Not to mention the cost, which can be 1.5 to 2 times higher than an equivalent LCD panel.
OLED has fundamental strengths over LCD that will open up the possibilities for how and
where displays are used in the world around us.
LG Display has a consumer OLED television that is only 2.57mm thick, they are working
on transparent OLEDs that can integrated into glass panels, and various OLED manufacturers
are working towards foldable displays.
With continued improvement OLED displays look set to revolutionise the way we consume and
view information in the world around us.
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