Every innovation comes from a Scientific theory. Here we discuss human eye limitations regarding visibility and the journey of the LED to the OLED display.
Before we jump on this topic little part of history you must know which scientist is behind this.
History of Led
In the early 1960s LED (Light Emitting Diode) was developed by Nick Holonyak Jr.Initially. At that time LEDs were used as indicator lights on electronic devices such as calculators and watches.
Later in the 1970s, technology improved rapidly, with higher brightness and better color options. This improvement continues and in recent days displays are well energy efficient and more precise in colors.
Scientific facts for LCD/led/oled
3 factors must understand which is important for LCD/LED/OLED.
- Light
- Material ( Which material is used to display different colors)
- Human Eye ( How the human eye sees an object and what are the limitation )
light
Light consists of atoms and their sub-particles electrons, protons, and neutrons. Electrons are charge-carrying particles that revolve around the nucleus like planets revolving around the sun.
Whenever extra heat or extra electric source is given to these sub-atomic particles it radiates photons to the surroundings.
Photons are the energy packets that carry energy and the amount of energy decide how long this can travel
Light is an electromagnetic spectrum. This spectrum can be visible to Human eyes because its wavelength lies between 380 to 700 nanometers.
How does LED DIsplay work?
The LED display is the light-emitting diode display. This display contains 5 layers to process and shows the image as output.
These are
- Back panel
- Substrate heat sink
- LCD panel
- Color filter
- Glass screen
Some fundamentals term used while explaining display feature
Pixel – Pixel is the smallest part of an image. It has a specific size according to the display quality. More the smaller the pixel size in a unit area more will be the display quality.
Avg size of a pixel is 0.3mm*0.3 mm and there are 3 different colors inside a pixel red, green, and blue. These colors can be changed to any color by changing the intensity of light.
If the pixel size is 1 inch by 1 inch then the human can distinguish the individual color but if the pixel size is smaller, then it’s difficult to distinguish individual colors.
Due to the limitation of the human eye, it is hard to differentiate the color of the subpixel level. Each pixel has different position and color data and this data is stored in a digital form for future reproduction of the image like (01001010)(10010101) etc
how LCD display works?
There is a uniform backlight source where light is always in the ON position while giving power supply.
After the Backlight, a diffuser is placed for distributing the light evenly to the color filter, and white color is shown as the output.
To display different colors in a pixel need to change the intensity of light. Here LCD plays its role to change the intensity of light.
The polarization of the LCD sheet has crystals that can be adjusted and get different brightness levels in the subpixels.
It converts the digital signal to a restored electronic signal. These electronic signals are now fed into the circuit and the LCD crystal rotates, polarizing the light. In this way, the display produces different colors and images.
The disadvantage of LCDs are
- Color reproduction is not correct. This is because when we did not get the perfect black color due to the backlight is always on.
- Require more Electricity.
Oled Display
OLED means Organic Light-Emitting Diode. it is discovered by Alan Heeger, Alan MacDiarmid, and Hideki Shirakawa in 1970 and they get a Novel prize in chemistry in 2000.
How Does Oled Display Work?
In this device, molecular energy is considered rather than atomic energy, and semiconductor is also important for the electronic device.
In an OLED, the HOMO (Highest Occupied Molecular Orbital) has the highest energy level occupied by electrons, and LUMO (Lowest Unoccupied Molecular Orbital) has the lowest energy which was unoccupied by electrons. The energy difference between HOMO and LUMO energy levels is the reason for the emission of light.
When a voltage is applied across the device, electrons from the HOMO level are excited and move to the LUMO level. This makes a positively charged Hole in the HOMO level.
The excited electrons and the holes move toward the emissive layer of the device. when they recombine with each other these sub-particles release energy in the form of light.
The color of the emitted light is determined by the energy difference between the HOMO and LUMO levels.
Organic materials that are used in the OLED affect the energy difference between HOMO and LUMO. Materials with a lower HOMO-LUMO gap can produce light with higher efficiency and brightness.
while materials with a larger gap may produce light with a longer wavelength. Careful selection of organic materials with appropriate HOMO and LUMO levels is essential for the design of efficient and high-performance OLED devices.
ORGANIC MATERIAL used in the Oled device
Organic materials are like natural-based compounds of carbon atoms. These Carbon atoms bonded with other elements like hydrogen, oxygen, nitrogen, and other elements.
These compounds are used as active components in OLEDs, solar cells, and transistors.
The properties of the material are flexibility, lightweight, low-cost manufacturing, and other advantages over traditional inorganic materials such as silicon.
some examples of organic materials used in OLED devices that have high energy levels include:
- The material used in the Emissive layer in OLED displays tris(8-hydroxyquinoline)aluminum (Alq3) and N, N’-bis(3-methyl phenyl)-N, N’-diphenyl benzidine (TPD).
- Polymeric materials are organic materials used as hole transport, electron transport, or emissive layers in OLED displays. Examples include poly(9,9-dioctylfluorene) (PFO) and poly(phenylene vinylene) (PPV).
- Phosphorescent materials: These are organic materials that can emit light through a process called phosphorescence. Iridium (III) complexes are used as dopants (additional elements used in a specific material).
- TADF (Thermally Activated Delayed Fluorescence) materials: These are organic materials that have high efficiency and color purity. They are often used as dopants(additional elements) in OLED displays. Examples – 4CzIPN and TCTA.
The use of organic materials with high energy levels helps to improve the efficiency and performance of OLED devices. The selection and combination of materials depend upon the specific requirements of the device, such as color gamut (showing different colors), brightness, and lifetime.
Advantages of OLED display
OLED (Organic Light Emitting Diode) displays have several advantages and disadvantages, as outlined below:
Advantages:
- Better Contrast: OLED displays have a higher contrast ratio (ratio between white and black color) as compared to traditional LCD (Liquid Crystal Display) screens, This means OLED can produce deeper blacks and brighter whites. The output of images and videos appears more vibrant and realistic.
- Flexible and Lightweight: OLED displays are made with flexible substrates(the base of the OLED show, is made with Silicon), which allows for the creation of curved or bendable screens. Mainly used on Mobile.
- Lower Power Consumption: This is because it does not need any Backlight. Each pixel in OLED has its own light to generate.
- Fast Response Time
Disadvantages:
- Limited Lifespan: OLED displays have a limited lifespan compared to LCD screens because the organic materials used in OLED displays get worse over time. This is the reason for the loss of brightness and color accuracy over time.
- Burn-In: OLED displays can be easily damaged by burn-in when static images or logos become permanently “burned” into the screen. This problem can be avoided by implementing pixel shifting, screen savers, and automatic brightness adjustment techniques.
- Cost: OLED displays can be more expensive to manufacture compared to traditional LCD screens, which can make them more expensive for consumers.
What is the difference between AMOLED and OLED displays?
Both AMOLED (active matrix organic light-emitting diode) and OLED (organic light-emitting diode) are similar display technologies.
How they control the flow of electricity to each individual pixel makes a difference. Here are some key differences between AMOLED and OLED displays:
- Active matrix: AMOLED displays use an active matrix of transistors to control the flow of electricity to each pixel, while OLED displays use a passive matrix that is less precise.
- Refresh rate: AMOLED displays have a faster refresh rate than OLED displays, which makes them more suitable for applications like gaming and video playback
- Power consumption: AMOLED displays typically consume less power than OLED displays because the active matrix allows for more precise control of the pixels.
- Cost: AMOLED displays are generally more expensive to produce than OLED displays due to the additional active matrix components
conclusion
In today’s scenario, most electronic devices use LCD or OLED displays. The mobile industry uses AMOLED displays for flagship devices whereas Apple is using Super Retina XDR display which is also an OLED display.
From my point of view, LCD shows more natural color than AMOLED but in case of power consumption, AMOLED wins most of the cases.
Which display is your favorite comment below?
