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"Depending on the configuration, it is also possible to display navigation instructions or other vehicle information, such as active cruise control or check control warning messages. It makes no difference what the weather conditions are. Whether you're driving through rain, fog, darkness or direct sunshine, a light-sensitive sensor adjusts the brightness of the image to the environment. This automatic brightness adjustment by the HUD means it is no longer necessary for the eyes to adjust to the difference in brightness between the road and the interior of the vehicle. And this by no means exhausts the potential of the Head-Up Display. "We are very much in the early days of a sensible development which will minimise traffic risk," said Gunnar Franz.





Glass and plastic - a powerful combination against heat

But high-technology windscreens cannot only be used as projection screens, they also protect the driver in many respects - for example, against excessive heat. In the height of summer, parked cars can quickly turn into ovens. "Of course, how quickly a car heats up to a given temperature depends on the intensity of the sunshine, the size of the interior of the vehicle, the size of the window and many other parameters," Dr Katrin Ludwig of the BMW Group explains the phenomenon. "Temperatures of over 50 degrees Celsius can easily be reached."



The radiation from the sun is made up of a variety of different types of radiation - it covers the electromagnetic spectrum, including a range of visible and invisible rays, from short-wave x-rays to long-wave radio waves. The largest proportion of the light is in the yellowish green sector of visible light. However, the presence of red and blue light means that we perceive visible light radiation as white. The majority of non-visible sun radiation is infrared radiation - it is primarily responsible for the unwanted build-up of heat in the car. Infrared covers the range from around 780 nm to 1 mm wavelength and was discovered over 200 years ago by Wilhelm Herschel. He deflected sunlight through a prism and broke it down into the individual colour ranges. Using a thermometer, he discovered that there was an increase in temperature cause by radiation beyond the red radiation in the visible spectrum - infrared, which is also known as heat radiation. If you wish to prevent the interior of the car heating up too much, the primary aim is to reflect the infrared radiation at the surface. To date, this could be achieved, for example, by protecting the windows of a parked car with a reflective cover. But as a vehicle can also heat up when in motion, the challenge for vehicle engineers lay in making the windows of the vehicles more impenetrable for infrared radiation - for example, using a compound glass with an embedded metallic intermediate layer: "This provides very good protection against infrared, but the metal not only reflects infrared radiation, but also protects the whole interior from radiation of all kinds and thus, for examples, affects reception for communications systems," Dr Katrin Ludwig of the BMW Group explains the problem. "We found the solution to this challenge in conjunction with 3M and Saint-Gobain Sekurit Deutschland. The groundbreaking compound glass technology developed as part of a joint project made it possible to prevent the greenhouse effect in the interior of the vehicle for the first time. 500 ultra-thin plastic layers are embedded into the screen, so each of the layers is just 0.00001 mm thick - around fifty thousand times thinner than a human hair." The benefits over conventional glass: The interior air temperature of a car parked in the sun for 90 minutes is about 5 degrees lower and the surface temperature of seats and storage areas is reduced by around 10 degrees Celsius - which represents a noticeable relief for the driver. At the same time, it means the air-conditioning system can cool the car enough at the beginning of the journey, which in turn translates into reduced fan noise and improved fuel consumption.


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