In recent years, with the explosive growth of industries such as the Metaverse and augmented reality displays, automakers have introduced various demands for in-car interactions, entertainment, office functions, navigation, and more. However, traditional displays are opaque and cannot be used in the limited space inside vehicles. Utilizing nearly 60% of the car’s surface area—its glass—as a transparent display is the best solution. Transparent displays include not only the popular HUD (Head-Up Display) but also window displays, instrument air imaging, and medium-free instruments. These technologies include DLP projection, OLED, Micro LED, and holographic technologies.
1. Transparent LCD Displays
Transparent LCD screens are not a new technology, having been in use for quite some time. One of the most well-known applications is the transparent display case used in retail showcases.
A transparent LCD screen is essentially an incomplete liquid crystal display that omits the traditional backlight unit, allowing objects to be placed between the backlight unit and the display layer. The transparent LCD screen requires a box as the backlight unit for proper functioning. Since these screens are not self-emissive, they need an external backlight to be visible. When not powered on, they appear black and not transparent.
On December 20, 2022, Japan’s JDI Corporation unveiled its latest transparent LCD display product—“Rælclear”, a 20.8-inch display with a light transmittance of 84%. The company claims it to be the world’s most transparent liquid crystal screen. When not displaying content, it looks almost identical to a glass surface. Once powered on, it transforms into a display with a resolution of 1280 x 720p, a 120Hz refresh rate, a 300cd/m² brightness, and the ability to display over 40 billion colors, meeting display needs for showcases and medical examinations. JDI stated that the Rælclear LCD display was expected to be showcased at CES 2023 and would be mass-produced by Fall 2023.
2. Transparent OLED Displays
A transparent OLED display uses self-emissive organic OLED technology. When powered off, it appears as a transparent glass screen, blending harmoniously with the surrounding environment. This futuristic design offers users a stunning visual experience.
At SID 2023, BOE globally debuted a 49-inch transparent OLED smart car window that uses white OLED technology, achieving a transparency rate of up to 40%. The display offers uniform color and clarity, allowing the blending of in-car scenery and road views, enriching the travel experience.
Visionox also showcased an OLED transparent display demo at the 2024 Optical Expo.
3. LED Transparent Displays: Mini LED/Micro LED
In recent years, as the demand for LED displays has grown and application areas have expanded, LED transparent displays have emerged as a new force in the industry. Thanks to their slim form factor, no need for a steel frame structure, ease of installation and maintenance, and excellent transparency, LED transparent screens have found applications in glass curtain walls, stage displays, outdoor advertising, and new retail industries. They are becoming increasingly prominent.
Micro LED transparent technology enables windshields and windows to function as equal displays. Flexible Micro LED technology enhances vehicle design. Even under direct sunlight, the high brightness and contrast of Micro LED displays remain clear. With their high brightness, contrast, flexibility, transparency, and exceptional reliability, LED transparent displays provide a comprehensive solution for automotive displays.
These displays can be adapted to different environments, including car side windows, smart storefronts, and commercial displays, providing a wide range of infotainment content.
4. Thin Film Electroluminescent Displays (TFEL)
Principle: The LUMINEQ® Thin Film Electroluminescent (TFEL) display consists of a solid-state glass panel, electronic control circuits, and power supply. The core of the thin-film electroluminescent glass panel is made up of a phosphorescent layer sandwiched between a transparent dielectric layer and lateral and vertical electrode matrices.
The durable display screen contains a transparent electrode layer and another non-transparent electrode layer. When both electrodes are transparent, the display becomes transparent, with a transparency of over 80%. The circuit board containing the driving and control electronics is connected directly to the back of the glass panel. By applying voltage to the lateral and vertical electrodes, the pixels on the display light up, causing the intersecting regions to emit light.
5. Reflective Imaging: Floating Instrument Panels/Holographic Assistants
Floating Instrument Panels have a strikingly futuristic and cool appearance, often seen at major auto shows and in concept car designs. In recent years, with continuous efforts from various manufacturers in the automotive display field, this concept product has gradually been applied to real cases.
Interactive air imaging technology revolutionizes traditional displays and human-machine interaction by using a negative refraction flat lens and light-field reconstruction principles. This technology allows light to converge in the air to form real images without the need for any medium. Combined with interactive control technology, it enables direct interaction between users and floating images.
Easpeed Technology’s non-contact smart in-car solutions include floating instrument panels, holographic entertainment screens for the front passenger, rear central armrests, and seatback displays, enhancing the intelligence and richness of human-vehicle interactions.
The Prism Holographic AID—the Aerial Intelligent Display System—blends HUD integration, innovative UI/UX, software applications, and multi-modal interactions to create a user-friendly, intelligent driving space, providing drivers with an entirely new driving experience.
The airborne, medium-free imaging system integrates essential instrument information, replacing traditional car instrument panels with advanced 3D holographic visuals, fulfilling the intelligent mobility needs of the future.
6. Projection Displays
Projection displays in automotive applications offer a variety of innovative functions, such as driving assistance, human-machine interaction, and entertainment. These include ceiling displays, transparent window displays, entertainment screens, AR-HUDs, smart surfaces, and laser headlights, creating vast market opportunities for automotive displays.
For example, the core of the AR-HUD projection system is the optical mechanism, which uses free-form mirrors to magnify the image before projecting it onto the road, enhancing the driver’s experience.
Other projection displays, such as side window projections, work similarly to AR-HUDs but do not use reflection or free-form mirrors to magnify the light path.
Holographic Films
Holographic projection is a hot technology that uses holographic films to create 3D, lifelike visual effects, making images more realistic. Holographic projection lighting not only draws attention to the car but also conveys safety information, such as displaying the message “STOP,” adding an extra layer of safety to the vehicle.
Films are widely used in various fields, from smart car cabins to 5G phone covers and ID cards, with new types of materials and applications constantly emerging. For example, BASF produces Bayfol® HX photosensitive polymer films, which have significant potential for advancing automotive lighting to new heights.
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