With the arrival of Apple iOS 13 and Android Q Beta OS, one of
the more interesting—and significant—enhancements from the
operating systems was the addition of dark mode as an option for
smartphone screens. While some applications previously offered dark
mode as an option, the ability now to set up dark mode in the OS
can help smartphone users more fully utilize and experience this
new display mode.
For the industry, dark mode may help boost the adoption of
AMOLED panels in the smartphone display market.
LCDs are a type of liquid-crystal display that use
liquid-crystal molecules as the switch that polarizes the light
illuminated by the backlight to display the video signals being
transmitted. LCDs cannot be illuminated without the backlight unit.
In comparison, an organic light-emitting diode (OLED) display is a
self-emitting device in which diodes and pixels produce their own
light and no external light source is needed. The variation in the
way light is produced by each technology translates into
fundamental differences between LCD and OLED displays in power
consumption and display performance.
For AMOLED, the benefits of dark mode are clearly seen in three
display panel aspects: power consumption, contrast ratio, and
visual defects.
Benefits explained
In discussing the first factor, power consumption, worth noting
is that an LCD panel has two power-consuming mechanisms. The first
is the thin-film-transistor (TFT) and liquid-crystal switch array,
driven mainly by the power voltage and accounting for 10-30% of the
total power consumed by the LCD module. The second is the backlight
unit (BLU), also driven by the power voltage but representing a
much larger share—70-90%—of the total consumed power.
This means the backlight unit is the single most power-hungry
component of the LCD panel. Until recently, the OS in both PCs and
smartphones utilized the default light mode, which makes the high
brightness of LCDs a necessary feature despite the high power
consumption involved. In dark mode, the LCD backlight unit is still
on, but power in the TFT and liquid-crystal switch is reduced. Even
with this accommodation, however, the overall reduction is minor in
LCD power consumption since the LCD backlight, the biggest power
hoarder, remains lit.
Power consumption works differently in AMOLED displays, which
are self-emitting devices driven by the power current, not by the
power voltage. In dark mode background, some OLED display pixels do
not need to be illuminated, instead lighting only the display or
the on-screen characters on screen. As a result, power consumption
will be largely reduced if a black background—in other words,
dark mode—is used by a smartphone.
Power consumption will be a critical factor for the coming 5G
smartphones, especially because the 5G baseband can consume a lot
of power. By cutting back power consumption in the screen, it will
be easier to extend the 5G smartphone’s standby time.
The second benefit provided by dark mode is in contrast ratio,
or the proportion of the darkest black to the brightest white on
the screen. While local dimming is now available as a feature in
LCD panels to make blacks appear deeper and richer, the backlight
required for illumination is still on and cannot be switched off,
preventing full blackness in color from being achieved.
In comparison, AMOLED does not have this problem. Using
self-lighting pixels capable of switching on and off individually,
black colors are deep and rich. And with dark mode enabled, most
pixels are shut down, allowing contrast to be maximized to the
fullest. AMOLED technology is thus more suitable for high contrast
ratio in dark mode.
The third benefit from dark mode relates to visual defects. With
the backlight always on in LCDs, visual defects—such as mura, a
dot or spot of blue—may be obvious even in dark mode. Taken
from the Japanese word unevenness or blemish, mura is more common
in LCD, a result from various possibilities, such as impurities in
the liquid-crystal matrix. Mura is also a challenge in OLED but for
different reasons. With each pixel as its own emitter of light in
OLED displays, inconsistency from pixel to pixel is inevitable.
As we analyzed in the
Smartphone Display Intelligence Service, AMOLED technology has
had difficulty establishing constant, persistent presence in the
smartphone display market. The challenges include high costs, the
complicated manufacturing process, and the lack of flexibility in
production.
In comparison, low-temperature polysilicon (LTPS) TFT-LCD has
proven to be very-cost effective and is the mainstream technology
used for smartphone displays.
LTPS TFT-LCD also benefits from many new form factors, such as
screen notches, hole-punches, and so on. AMOLED displays, in
contrast, lack the flexibility needed to produce these new form
factors.
In the short term, AMOLED displays cannot compete with LTPS
TFT-LCDs in the smartphone form factor. Meanwhile, the foldable
OLED display is an attractive form factor that LCDs cannot achieve,
but the high cost and the complex production difficulties of the
foldable screen hamper its growth.
However, the dark mode capability may yet provide AMOLED the
necessary advantage to penetrate the smartphone display market more
rapidly compared to the past, especially if only a change in
software, not hardware, is involved. If consumers start getting
used to dark mode, AMOLED displays will rapidly spread throughout
the smartphone display market.
Dark mode makes screen notches and holes unobtrusive
When the OS is black, screen-form factors like notches and holes
will not be as obvious. Screen notches and holes are not so much
functional parts of the display but instead serve as a receptacle
for the front-camera module, infrared (IR) module, and facial
recognition module. In dark mode, smartphone users won’t notice the
existence of a notch or hole because the whole screen will show as
a dark background.
Given the lack of flexibility in manufacturing or production,
AMOLED display makers have long struggled with both OLED front-end
and back-end module processes to integrate the form factor of
either the notch or the hole. Furthermore, AMOLED displays
sometimes miss opportunities in the market because introducing a
new process is much more difficult in OLED than in LCD. But as the
screen notch or hole becomes less obvious with refinement of the
technology, the pressure borne out of introducing new processes can
gradually ease for AMOLED display makers.
Since 2019, the technology for under-the-screen fingerprint and
fingerprint on display (FoD) readers has taken off, thanks to the
promotion of FoD by Chinese smartphone brands, as we pointed out in
an analysis in the Display Dynamics article,
Display fingerprint (FoD) solutions for TFT LCD displays.
But the introduction of FoD gave AMOLED displays an advantage over
LCDs, according to research in the
Display Fingerprint Technology & Market Report – 2019,
impacting the latter despite their inclusion of new features like a
bezel-less screen as well as the more discreet screen notch or hole
for a streamlined appearance.
Now with the arrival of the new dark mode and given the ramp-up
in capacity of new Chinese OLED display makers, Chinese smartphone
brands will have even more reason to switch from LCD to AMOLED
display use. These developments will affect the long-term prospects
of the LTPS TFT-LCD space while leaving relatively untouched the
market for amorphous silicon (a-Si) TFT-LCDs, projected to remain
stable as their use continues in the low-end smartphone and feature
phone market.
The key to how quickly the market transforms will depend on how
fast end-users embrace the dark mode feature for their
smartphones.
Rigid OLED vs. flexible OLED in dark mode
Dark mode presents no distinct differences whether the feature
is used in rigid OLED displays or in flexible counterparts where
the screens can be curved or foldable. Nevertheless, newcomers to
the panel-supply industry, especially those in China, are all
choosing the flexible form factor as their OLED technology of
choice, based on the following considerations:
- OLED fabs in China are all established through government
subsidies, and fabs featuring fresh technology—flexible OLED is
newer and more advanced than rigid—are considered to have an
edge in obtaining the subsidies. - Chinese makers are leaders in LTPS TFT-LCD smartphone display
shipments and capacity. But because rigid OLED and LTPS TFT-LCD are
both glass-substrate-based, the use of rigid OLED does not impart
enough differentiation to stand out in the market - The cost-performance ratio of rigid OLED displays is lower than
that of flexible OLED displays. The large profits of Samsung
Display in its use of flexible displays has driven this point home
for Chinese panel suppliers. - Apple skipped rigid OLED and went directly to flexible OLED
when it released the iPhone X. And the iPhone is always on the
forefront of innovation.
Nearly all Chinese OLED display suppliers today train their
focus on flexible OLED, leaving the rigid OLED market almost
entirely to Samsung Display, as we reported in the
AMOLED & Flexible Display Intelligence Service. However,
flexible OLED displays are not easy to make, which makes their
increasing deployment on high-end smartphone models that much more
remarkable.
For Chinese panel manufacturers, the introduction of dark mode
widens their chance to compete in the market, even as they continue
to struggle with low yield rates, high depreciation costs, and
other issues. <span/>The
situation is especially acute for Chinese OLED display makers, who
are said to be producing flexible OLED displays without the
flexible form factor, such as 2.5D, to cut costs and narrow the
gulf between OLED and LTPS TFT-LCD.
Now with a new OS like dark mode, there are greater advantages
given to AMOLED displays compared with LTPS TFT-LCDs, and this
might be helpful for Chinese OLED display makers to introduce their
OLED panels.
Next year will be a critical time for the smartphone display
market, with several factors influencing how the smartphone display
space will fare in 2020. These factors include the progress of FoD
reader technology in LTPS TFT-LCD panels, the new module capacity
and capability of Chinese OLED display makers, whether middle=end
smartphone models switch to OLED displays from the existing LTPS
TFT-LCD technology, and the ramp-up of new fabs among Chinese
flexible OLED display makers.
Into this complex, dynamic mix we can add one more factor: the
acceptance of the new dark mode by end-users. It remains to be seen
whether the feature will create enough interest to help lift AMOLED
to new levels of use and influence in the display panel market.
David Hsieh is research & analysis director for
displays at IHS Markit
Posted 29 August 2019