Brandon Seiser, Product Marketing Engineer, Texas Instruments
Recently, there has been a big push in the automotive lighting industry to improve both vehicle headlight functionality and driver visibility, which has led to the development futuristic headlight technologies such as adaptive driving beam (ADB) and high-resolution headlights.
Adaptive beam headlights
Drivers use headlights to illuminate the road ahead, along with any potential hazards. Basic headlights typically employ two modules: a low-beam base light and a manual on/off high beam. Typically, headlights use both a low-beam base light, which allows better visibility of the road and of the vehicle to other drivers, and a high-beam light, which is used for greater intensity in illumination or for signaling, and requires a driver to manually switch on and off the high-beam light. Drivers rarely encounter situations necessitating the use of high-beam headlights, however, and end up using this option sparingly.
In an effort enhance visibility and assist drivers, ADB headlights have been developed. An ADB system automatically controls the entire headlight, including high beams, enabling drivers to focus on the road and stop toggling their high beams on or off based on lighting conditions and the presence of oncoming vehicles.
The goal of an ADB automotive exterior lighting system is to increase road safety by maximizing the amount of light projected onto the road without affecting oncoming drivers. For vehicles without high-beam field-of-view (FOV) segmentation, also known as pixelated high beam lights, ADB system functionality includes turning high beams on and off automatically. However, new technologies enable segmentation of the high-beam headlight FOV – in other words, they can turn portions of the high-beam headlight on or off individually.
For example, if a high-beam headlight has 12 segments, only a few of these segments need to be turned off to prevent drivers of oncoming vehicles from experiencing glare while the remaining segments can still illuminate the road. Figure 1 gives an example of a nighttime driving situation where a driver is approaching an oncoming vehicle, a traffic sign, and a pothole in the road. The driver’s vehicle is not equipped with an ADB system, so only the vehicle’s base light illuminates the road. Figure 2 represents the same driving scenario as Figure 1, except this time the driver’s vehicle is equipped with a 12-pixel segmented ADB system. The segmented ADB system is illustrated with red boxes to highlight each pixel’s illuminated area in the high beam FOV.
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Figure 2: Headlight FOV with a background 12-pixel matrix. Each pixel is illustrated with the red segment in the high beam FOV
From Figures 1 and 2, we can see that adding resolution to the vehicle’s high beam can help increase the light projected onto the road and improve visibility. With DLP technology, a third high resolution module with over one million pixels can be added to further increase the amount of light on the road and support many new applications. Figure 3 shows the example headlight FOV breakdown from Figure 2 with a high-resolution region.
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Figure 3: DLP headlight FOV breakdown
In Figure 3, the high-resolution module is placed to cover some area in both the low-and high beam FOV. This positioning enables the DLP headlight module to project high-resolution symbols on the road in the “HR graphic area” in the low beam FOV in addition to providing ADB support (high-resolution area in the high beam FOV). The DLP technology is a great fit for symbol projection because of the resolution needed to create high quality, comprehendible symbols (such as a right turn arrow indicating that the driver needs to turn right). The relationship between resolution and the clarity of symbols projected from a headlight is amplified compared to standard projection displays due to the orientation of the vehicle’s headlights. Because the headlights are not projecting on a surface perpendicular to the projection source, the projected symbols can easily become stretched out and become incomprehensible to the driver without enough angular resolution.
High resolution headlights
High resolution headlights can add value to vehicles by expanding applications to improve advanced driver assistance system (ADAS) functionality. These futuristic applications can include structured light, which could help next-generation ADAS to better detect and identify objects and obstacles in the road; traffic sign dimming, to prevent front camera glare; and weather detection, to remind drivers of potentially hazardous road conditions.
A high resolution headlight module can project patterns designed to function as a depth sensor while being unnoticed by the driver. This application is known as structured light. The ADAS processor uses the front camera to capture the response to the pattern and determine whether any objects are in the path of the vehicle. If the ADAS system detects any debris or potholes, it can alert the driver of the hazard through the symbol-projection feature. This is depicted in Figure 4, where DLP automotive technology has been used in a headlight and front camera system recognize and alert the driver to a pothole.
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Figure 4: DLP headlights working with the ADAS camera systems to detect and alert drivers to objects in the road
Besides pothole and debris detection, structured light can also improve an active suspension system’s performance at night. Many active suspension systems struggle with nighttime performance because of poor system visibility, but projector headlights can greatly improve the performance of active suspension systems.
OEM and Tier 1s have expressed a desire to move the ADAS front camera sensor near or inside the headlights. One downfall of this new location is that the ADAS camera systems can suffer reduced performance at night near traffic signs. Traffic signs can interfere with ADAS front camera performance and accuracy at night if the adaptive headlights reflect light directly back to the light source. When a camera has a light shined directly onto its lens, the camera sensor “blooms” or oversaturates and completely washes out the image, which prevents any real-world data from reaching the ADAS system and is thus unable to alert the driver to potential hazards. Using high resolution projection technology, an ADAS system can create a highly efficient mask and turn off the light directed at the traffic sign so that the vehicles front end camera ADAS system functions properly and the driver can better comprehend the traffic sign. Traffic-sign dimming is a must-have feature for ADB when used on city streets and highways, as traffic signs are prevalent on these types of roads. Figure 5 depicts a projector headlight dimming a traffic sign but illuminating a child trying to cross the road.
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Figure 5: Headlights highlight a child attempting to cross the street while dimming the crosswalk sign to reduce glare
High-resolution headlights can also be used to help detect the weather condition during nighttime driving. Some vehicles can detect weather with just a camera during the day, but it is more challenging at night due to poor lighting conditions. With high-resolution headlights, the vehicle can increase the intensity of light to a specific area to help improve camera visibility. By enabling the vehicle’s ADAS front camera system to detect weather conditions at night, the vehicle can automatically enable safety features or configurations to better handle hazardous conditions, including fog and icy roads.
Evolving headlight technologies are improving the functionality of vehicle headlights and enabling new features and applications for vehicles. ADB headlights maximize the amount of light on the road, structured light warns the driver of upcoming hazards, traffic sign dimming capabilities are being added to improve ADAS performance, and weather detection is used to help the vehicle adapt to surrounding conditions. In the future, we believe headlights will be used as a method to communicate with the driver, other vehicles and other road users. In order for the headlights to communicate, high resolution is needed to create clear, high quality commendable symbols.