Display Technology: Exploring the Evolution from CRT to OLED

       Display technology has come a long way over the past few decades. From bulky, power-hungry cathode ray tube (CRT) displays to today’s sleek, energy-efficient flat panel displays, the ways in which we interact with computers and other devices have been completely transformed by rapid advances in display capabilities.

        In this blog post, we will explore the key developments and innovations that have shaped the evolution of display technology from early CRTs to modern organic light-emitting diode (OLED) displays. We will look at how each new technology improved upon its predecessor and paved the way for the next generation of displays.

Traditional Display Technologies

        In the early days of computing, CRT displays were the only viable technology used to visualize electronic data and text. But they came with many limitations. Better technologies like LCD and LED displays were later developed to overcome the drawbacks of CRTs.

Cathode Ray Tube (CRT) Displays

        The cathode ray tube display contains a large vacuum tube with an electron gun that shoots beams of electrons onto a phosphorescent screen to produce images. CRT displays work by firing electrons from the cathode gun through the vacuum tube. Magnetic coils around the gun’s neck then guide the electrons in the right direction so they bombard on the screen coated with red, green, and blue phosphor dots.

        This makes the phosphor glow and create images. Varying intensities of the electron beam and directing them to hit different colored phosphors produces on-screen images. An internal electron beam sweep system fires the beams across the screen horizontally to create each row of the display.

          CRT displays came into prominence in the early 20th century. They were adopted for use in early computers and television sets due to their ability to produce sharp, flicker-free images. However, CRT displays had several disadvantages:

• They were bulky, heavy, and consumed a lot of power. This made them impractical for use in small, portable devices.
• They contained large circuitry and high voltage components. This often led to stability and safety issues.
• They emitted significant electromagnetic interference that could disturb operation of nearby devices.
• They had considerable geometric distortion and glare issues. This affected image quality and viewability.
• They were prone to flickering and slow refresh rates that could cause eye strain.

         By the late 20th century, it was clear that CRT technology was too limited for the needs of modern computing. This drove research into new “flat panel” displays based on LCD and LED technologies.

Liquid Crystal Displays (LCD)

        Liquid crystal display (LCD) technology offered a thinner, lighter, and more energy-efficient alternative to bulky CRT displays. An LCD screen contains a thin layer of liquid crystal solution sandwiched between two electrically charged plates made of glass, plastic or other transparent material. When voltage is applied to the plates, it untwists the liquid crystal molecules and allows light to pass through. The LCD glass plates contain polarizing filters that manipulate the light and color filters that create red, green and blue subpixels. By precisely controlling the voltage across different sections of the LCD grid, the crystals can twist to varying degrees and modulate the amount of light passing through them. This forms images on the screen.

• Compared to CRT displays, LCD screens provided multiple advantages:
• Much thinner and lighter, enabling development of flat panels.
• Use passive matrix or active matrix addressing for faster refresh rates.
• Require low operating voltages and consume little power.
• Generate less heat and allow better temperature control.
• Offer wider viewing angles and higher contrast ratios.

        However, early passive matrix LCDs still had issues like slow refresh rates, narrow viewing angles, and poor color reproduction. But the development of thin-film transistor (TFT) active matrix LCDs in the late 80s overcame most of these problems and paved the way for the ubiquitous LCD screens we see today.

Advancements in Display Technology

        While LCD displays represented a major leap forward, researchers continued to find ways to enhance display capabilities through new technologies like LED and OLED.

Light Emitting Diode (LED) Displays

        LED displays use a panel of small, bright light-emitting diodes as pixels to create images. Compared to LCDs that require separate backlighting, LED pixels are self-emissive – they produce their own colored light. LED displays offer several improvements over traditional LCD technology:

• Higher Brightness – LEDs are up to 10 times brighter than LCD backlights. This improves screen visibility in bright environments.
• Wider Color Gamut – LEDs produce truer, more saturated colors covering over 100% of the sRGB color space.
• Improved Contrast – LEDs can produce true blacks by turning off completely without any light bleed.
• Faster Refresh Rates – LED displays have quicker response times and higher refresh rates up to 240 Hz.
• Greater Energy Efficiency – LED displays consume up to 40% less power than CCFL-backlit LCD panels.

        While early LED displays were limited to large outdoor screens, the development of ultra-thin edge-lit LED backlights allowed their adoption in slimmer TVs, monitors and laptops. OLEDs later built upon LED advances to further improve display performance.

Organic Light Emitting Diode (OLED) Displays

        OLED (organic light-emitting diode) displays revolutionized display design through the use of organic carbon-based compounds that glow when electricity is applied. In an OLED display, each self-emissive pixel is made of organic thin-film materials sandwiched between two conducting layers. When current is passed through, the organic material emits its own light.

        This gives OLED displays several benefits compared to LCD and LED displays:

• Lower power consumption – OLED pixels use less power as they don’t need separate backlighting.
• Faster response times – OLED’s higher refresh rates and microsecond response times reduce motion blur.
• Superior contrast – OLED pixels can switch off completely delivering infinite contrast ratios.
• Wide viewing angles – OLED screens maintain color accuracy and brightness at wider viewing angles.
• Thinner/lighter – OLED displays are incredibly thin, flexible and lightweight.
• Vibrant colors – OLEDs produce rich, vibrant and accurate colors with wider color gamuts.

       Thanks to these qualities, OLED technology is being adopted across everything from high-end smartphones and tablets to large flat-panel TVs and monitors. Their ability to be printed onto flexible plastic substrates also opens up new possibilities for bendable displays.

The Future of Display Technology

        Ongoing research is focused on developing new concepts like quantum dot and micro LED displays to enhance color quality, brightness, and energy efficiency even further.

Quantum Dot (QLED) Displays

        Quantum dots are semiconductor nanocrystals that can produce extremely pure monochromatic light.  It displays aim to improve the color performance of LED-backlit LCDs by using these nanocrystals as light-emitting materials. In a QLED display, a quantum dot film is placed between the LED backlight and the LCD panel. When the blue LED light passes through the quantum dots, they emit pure red and green light at very precise wavelengths to match the color spectrum. This allows QLED displays to render colors more accurately and vividly while using less power than traditional LED-LCDs.

        The quantum dots also improve efficiency by recapturing some of the light normally lost in the color filters of the LCD. This increases the luminance or brightness produced by the backlight unit. QLED TVs can achieve up to 100% color volume and produce high peak brightness levels over 1000 nits.While QLED technology is still evolving, it demonstrates how nanoscience can further enhance the capabilities of current display technologies.

Micro LED Displays

        Micro LED displays are an emerging display technology that promises to combine the best aspects of both OLED and LED displays. As the name suggests, micro LED displays use millions of microscopic LEDs as individual pixel elements. Each micron-sized LED pixel can be switched on/off individually like an OLED display. But as they are still LEDs, micro LED displays deliver the high brightness, longevity and efficiency associated with LED technology. By removing the need for backlights and filters, micro LEDs deliver perfect blacks, wide color gamuts, high brightness and contrast. They also enable ultra-thin flexible displays and large screen sizes.

Conclusion

        Display technology has come a long way from the bulky, unsafe, power-hungry CRTs to today’s thin, bright, energy-efficient OLED and QLED displays. Technological advances have been focused on making displays smaller, faster, safer, more colorful and power efficient while improving image quality. Ongoing innovations promise to further push the boundaries of what’s possible by enhancing color reproduction, contrast, brightness, and energy efficiency even more. Micro LEDs and other technologies still in development.