There are two main display technologies: LCD and OLED. LCDs use a backlight and liquid crystals to modulate light, while OLEDs are thin and emit their own light without a backlight. OLEDs can achieve higher contrast ratios and color gamuts than LCDs. However, LCDs are preferred for applications requiring static images due to OLEDs being susceptible to luminance decay over time. While OLEDs are becoming more common in mobile devices, LCDs remain the cheaper option for laptops due to tradeoffs in image quality.

1. What’s the difference
between LCD and OLED
displays?
By Mehmet Tugrul, Field Applications Engineer
for OSD Displays (an OLED panel supplier and
division of New Vision Display)

2. Display Technologies

3. • There are two main competing display technologies in the market
today: LCD and OLED. The mature and dominant technology is
the Liquid Crystal Display (LCD), while the up-and-coming
challenger is the Organic Light Emitting Diode Display (OLED
display). The main difference between LCD and OLED displays is
how they create the light and the colors of the image being
displayed. This leads to application dependent strengths and
weaknesses of either technology.
• OLEDs operate via a solid-state technology, where the individual
pixels can emit light in various colors and intensity without the
need for an additional light source or color filter. The light-
emitting portion of an OLED display is comprised of multiple
layers of very specific organic semiconductor materials which can
be adjusted to emit light in specific wavelengths. These organic
layers have a typical thickness in the order of 100nm. In addition,
no backlight is required, allowing for a very thin display module.

4. Layers of an OLED cell
The organic layers beginning on
the cathode side of the device
consist of several electron
transport layers, a recombination
layer and end with a hole
transport layer on the anode
side. The electron transport
layers in the OLED stack-up allow
movement of electrons from the
cathode toward holes supplied
from the anode. The electrons
and holes recombine in the
emissive recombination layer of
the film stack-up.

5. • This recombination relaxes the energy levels of the electrons, which
produces an emission of light. The wavelength of the emitted light is
dependent on the chemical composition of the organic materials used in
the recombination layer. The intensity of the light is controlled by the
amount of current flowing through the OLED’s organic layers. In OLEDs,
the individual pixels can emit red, green, or blue light, or – alternatively
– they emit white light, which must then pass through color filters.
• In LCD display technology, the individual pixels modulate light. An
applied voltage changes the orientation of liquid crystal molecules that –
in conjunction with a pair of polarizers – function as a light shutter by
either blocking or allowing light to pass through. LCD displays, therefore,
require an additional light source, either from reflected ambient light or
more commonly from a “backlight” (an array of LEDs arranged behind or
next to the LCD panel). LCD color can be created by either switching the
backlight quickly between red, green and blue, or – more commonly – by
adding color filters to the individual pixels. Because OLED displays don’t
require the additional backlight, polarizers, or color filter components of
an LCD module, they can be made much thinner than LCD displays of
equivalent size and resolution.

6. LCD Example

7. • OLED display technology can offer power-saving advantages over LCDs,
which is important, especially for battery-powered applications such as
mobile phones. An OLED’s power consumption will vary with image
content and brightness, as light is generated only at the individual pixels
needed to display the image. A dark image or a graphic on a black
background will consume much less power than bright images or
graphics. In contrast, LCD backlights must be ON while the display
operates. It’s possible to control individual zones of the backlight
separately to save power, but this added complexity is usually only
applied in larger displays.
• OLEDs can achieve a much higher contrast ratio if reflections from the
front surface are carefully controlled. If no current flows through an
OLED pixel, it does not emit any light. In contrast the shutter effect of an
LCD pixel does not block 100% of the light. Depending on the specific LCD
technology used and the angle of observation, a small percentage of the
light generated in the backlight can escape. This can wash out dark areas
of an image. It is possible but expensive to limit this light leakage to a
point where the contrast of an OLED and LCD display become
perceptually equivalent.

8. • RGB OLEDs naturally generate a narrow bandwidth of light. This
leads to very saturated primary colors and a wide color gamut.
This enables OLED technology to display colors which are not
easily accessible to LCDs unless RGB backlights or quantum dot
phosphors are used for the illumination. Often OLED colors are
used “as is”, however, for very high image color fidelity, such high
color saturation needs to be electronically ‘tuned down’, to match
the color bandwidth of the rendering chain.
• LCDs offer an advantage over OLEDs in applications where a
continuous static image is required. The light emitting materials
(also called phosphors) in OLEDs are affected by luminance decay
as a function of the total amount of current that has passed
through the pixel. This decay differs for red, green and blue
phosphors. The dimming effect is subtle, but when adjacent pixels
are illuminated at the same time it can become noticeable as an
undesired brightness variation or color shift. LCDs don’t suffer
from this dimming effect, which makes them a more suitable
solution for applications with static images or images with static
elements.

9. LCDs are still preferred technology for laptop applications due
to lower cost trade-off

10. • Another advantage of LCD technology is the wide variety of
different variations to choose from. Depending on the
application certain trade-offs can be very attractive. An
example is much lower cost for a laptop display compared to
a tablet. This is achieved by allowing poor image
performance when viewed from the direction the is usually
blocked by the keyboard. In a tablet where good viewing
performance is required from any direction, much higher
cost LCDs or OLEDs must be used.
• OLEDs offer an excellent solution for a variety of
applications: Glucometers and thermometers, fitness
trackers, professional audio equipment, Wi-Fi hotspots,
radar detectors, dive computers, biometric transaction
devices, and military communications equipment.

11. Fitness watches often use OLED
displays
They can be used to replace old TN
LCDs or add dynamic push buttons on
industrial equipment. They can be
customized to various resolutions,
FPC configurations, colors and shapes
(e.g. octagonal, round, etc.) and can
even be made into flexible and
transparent displays offering OLED
display panel suppliers some exciting
capabilities for their customers –
things that were previously
impossible with LCDs.

12. • New Vision Display and OSD Displays (a
Division of New Vision Display specializing in
OLED displays) are happy to discuss each
technology’s strengths and weaknesses, and
provide product designers with expert
guidance on choosing the right display module
solution for their design. Contact us today to
learn more!

13. Source:
• http://newvisiondisplay.com/difference-lcds-
oled-displays/