Ying Xiong weighs up the pros and cons of different head-up display solutions for transportation purposes
Dashboards in vehicles play an essential role in ensuring the driving is safe and smooth by providing relevant data such as speed, RPM, oil level, warnings, and so on. But as more and more data are presented on multiple screens in vehicles, critical information can sometimes become swamped or difficult to see. Moreover, glancing between the dashboard and the road can be dangerous, especially when drivers need to focus and keep their heads up.
Head-Up Displays For Drivers
The ability of head-up displays (HUDs) to reduce distraction by showcasing critical information in front of the driver explains why they have become increasingly popular in the transportation industry of late. There are two main head-up display technologies: projected HUD and emissive HUD.
The typical projected HUD solutions include TFT-/micro-LED-display HUD and DLP projector HUD. TFT-/micro-LED-display HUD uses two mirrors to project the images generated from a micro-LED display, while DLP projector HUD consists of a DLP projector, DLP optics, and HUD optics.
One major advantage is that the focal point is adjustable, e.g. 3 metres ahead of the vehicle. Eyes refocus more quickly when the driver’s attention switches from the road to the projected display. The projected content can be rich and colourful, and the solution is mature as it has been available and tested in the automotive market for years.
In terms of disadvantages, the setup is complex and occupies lots of space (typically 7-10 litres) in the dashboard. A special windscreen/coating is also required and the viewing angles are limited.
To complicate things further, the projector shakes when the vehicle shakes, resulting in blurry images, and they do not work with vertical windows and windscreens, making them unsuitable for buses, RVs, trucks or vans in most cases.
As emissive display technologies advance, some are becoming alternative solutions for creating next-generation head-up displays that do not require projected systems. The emissive display technologies that can be used for HUDs include micro-LED, TOLED, and Lumineq in-glass displays.
These solutions use transparent displays to show information in front of the driver. The electronics and flexible cables are compact and hidden, while the display parts are outside the dashboard. Micro-LED arrays are glued on the windscreen, the TOLED display is installed above the dashboard as a separate unit, and Lumineq in-glass displays are laminated in the windscreen.
The significant difference between an emissive HUD and a projected HUD is the focal point. The focal point of a projected HUD is adjustable, while the focal point of an emissive HUD is on the display, which is placed in the driver’s line of sight. This can arguably be a disadvantage or an advantage, depending on the driver’s preference.
The projected information ‘floating’ a few metres ahead of the driver allows the eyes to refocus faster, but some drivers may find it more distracting when mixed with real-world road conditions.
Besides the focal point, another big difference is the amount of space required for the setup. In this regard, emissive HUDs clearly win. Their construction is simple and requires little space in the vehicle’s interior. Instead of a complex projection system, the emissive HUDs consist only of compact electronics, a flexible cable and a display. The electronics are small and require around 0.3 litres of space from the dashboard, 20-30 times less than the projected HUDs.
Furthermore, emissive HUDs handle shock and vibration better. They work in trucks, buses, RVs and vans with vertical windscreens, because the information is shown directly on the display, unlike projected HUDs that require specific angles to project images properly.
Among these three emissive HUDs, Lumineq and mini-LED are made from inorganic materials, while TOLED is made from organic materials. Therefore, the local environment greatly affects the performance of a TOLED HUD, while the other two are immune from environmental factors including humidity, solar load and temperature.
Regarding optical clarity and transmission, the Lumineq in-glass HUD offers several advantages over TOLED and mini-LED. It is practically as clear as glass, with over 70% transparency, while TOLED has 40% and mini-LED 60%. It also has good clarity and minimal haze, while the other two have clarity and haze issues. The images from Lumineq in-glass HUD are viewable from 360° angles, both inside and outside the vehicles.
When it comes to the richness of the content, both TOLED and mini-LED can display colourful images, while Lumineq in-glass HUD is monochrome.