The development of multi-pixel LED technology has launched a huge leap in the development of the most obvious intelligent lighting system in the automotive industry. Today, the first hybrid LEDs offer smart headlights with more than 1000 individually controllable pixels. Ralph Bertram, who is working on advanced LED device concepts, and Norbert Harendt, who develops general lighting optics solutions from OSRAM Opto Semiconductors, say automotive lighting is just one of the potential areas of intelligent selective pixel control applications. Options used in general lighting, such as information displays for outdoor, indoor, retail or industrial applications, are very versatile.
Details of the "Omnipoint" demonstrators
Smart lighting has become an increasingly compelling trend topic, attracting not only the attention of the industry, but also attracting the attention of the general public. Trends such as smart homes, IoT penetration and advances in LED technology are some of the key factors driving market growth. Energy-efficient LED technology, intelligent control mechanisms and sensors to adjust user comfort lighting settings, and new concepts like human center lighting, energy conservation has become the forefront of consumers' minds.
So far, adaptive lighting has included changing the light intensity and color based on usage parameters such as check-in time or time of day. But there are many other areas of application where smart space adaptive lighting can provide end users with many benefits and open up new potential markets for solution providers.
Traditionally, the automotive industry has been at the forefront of many technological developments. Today's cars often represent the most advanced technology that many consumers have. Almost every aspect of modern cars is high-tech and uses the most advanced materials and solutions. As a result, automotive has become a platform for demonstrating technological development, as well as the potential and advancement of engineers and innovators. For example, the Adaptive Headlamp System (AFS) helps improve driving and road safety. These systems adjust the direction of the light, by illuminating the curve process, one side of the road or through the so-called adaptive driving beam (ADB) helps protect the oncoming traffic from glare, providing the driver with the best visibility.
So why not transfer to space adaptive lighting earlier? Most likely because the technical challenge is higher than other lighting systems. Changing the path of light requires moving parts such as tilting mirrors or moving lenses. In the past, it was impossible to provide an affordable, efficient and fully reliable solution that would also achieve the long lifespan required for professional lighting systems. With the continued miniaturization of LED technology, new possibilities have emerged that are expected to add another dimension to adaptive light sources: changing the beam pattern of the source without moving parts.
Application areas and requirements
Smart space lighting has become commonplace in some applications: when passing, the corridor lights up, the parking lot lights up only when the person is present, and the lights above the desk or kitchen area are automatically dimmed when not in use.
All of this can be done by adding sensors and intelligence to existing and new luminaires. For example, in the hallway, it is enough to light or dim the distance of 3-5 meters. In the office, this is already a different story: some people may just want to light their desk instead of the surrounding area. Others want a beam of light on the paper they are working on. Considering the airplane, train or car interior, it may only be necessary to light up the crossword puzzle that the passenger is working on, and not to disturb the passengers in the next seat that wants to sleep. This is also a very useful feature of home lighting - for example, if you prefer to read at night while your partner is sleeping early.
Museums or restaurants have different requirements for adaptive lighting. Today, they usually need to choose a more or less illuminating device with a rail system that can be manually adjusted by the luminaire. If you change the layout of their table or artwork, the lighting arrangement originally selected is usually not suitable. However, changing the luminaire is time consuming and therefore expensive. To avoid this, novel lighting systems require digital control and finer spot size, which makes it difficult or impossible to achieve by conventional means.
In store displays, the benefits of space-adaptive lighting are even more pronounced: even with the faucet on the tablet, even if you set up lighting accents from a remote location, you can save a lot of work and money associated with setting up merchandise displays. It also enables users to change the look and feel of the display in a temporary notification, even without touching it.
Technical challenge
Each of these application areas has different requirements for the necessary level of illumination and "granularity" - this means the size of each "pixel" to be illuminated. In Table 1, we try to estimate typical scenes, including feature size, source distance, and resulting beam angle.
Estimated "granularity" (= minimum point on the target) and optical parameters required for different applications
Looking at a set of parameters, the biggest challenge is the fine-grainedness of each single beam. In 2015, OSRAM began to showcase this application scenario with the “Omnipoint†concept [1]. In this case, nearly 100 Oslon square high power LEDs are assembled on the hollow sphere of the downlight configuration. Each LED equipped with its own narrow beam optics points in a different direction in the room. By individually switching or dimming each LED, you can smoothly adjust the light distribution in the room.
The point size on the target is equal to the "granularity" in the multipoint source
Through tremendous efforts in mechanics and optics, the fixture is able to meet the requirements of demanding office applications as described above and is closer to meeting store lighting specifications. However, applications that target small object illumination, such as reading lights or complex commodity lighting, require more pixels and smaller beams. In order to develop a system that meets these requirements, a different, more integrated technical approach is required.
More but smaller pixels require densely packed LEDs that can be individually addressed. Therefore, miniaturization of the system and its components is a key requirement that will allow the use of universal optics with hundreds of light sources. This, in turn, is critical to keeping the system simple and affordable.
Looking at the requirements in the table, the necessary illumination levels for each pixel of many applications can be met by using a 1mm arrangement. Each LED provides a typical 100 lumens and up to 300 lumens in overspeed mode.
However, in order to illuminate the entire room with these beams, hundreds or even thousands of pixels are required. Therefore, it is very important to have a high-intensity emitter that can be packed very closely together. Figure 3 shows an array of new chip size "packages" being developed that are no larger than the chip itself. In fact, it is designed as a surface emitting chip without any package or frame. Its compactness is ideal for dense arrays while still being managed by standard SMD equipment.
This new groupable LED provides the best compact size possible with LED components and helps meet the requirements of many application scenarios. But even with such an achievement, in some cases, the size of the entire LED array can be difficult to manage through optical components. In addition, driving LEDs still needs to be implemented in a passive matrix arrangement with external electronics. So the next step in the integration process will be multi-pixel LEDs.
Surface emitting chip size package array
Towards a multi-pixel source
To date, adaptive LED lighting systems, including automotive headlamps, have been operated with individually controlled chips for each lighting area. Now, the development of multi-pixel LED technology is driving the development of intelligent lighting systems, which are observable in the automotive industry.
Under the “μAFS†research project funded by the German Ministry of Research and Education (pronounced “micro AFSâ€), a group of German companies worked for three and a half years before September 2016 for the efficiency of adaptive headlamp systems. LED headlights. OSRAM Opto Semiconductors serves as the project coordinator and provides a broad range of expertise in the automotive industry as well as LED lighting solutions in the field of chip and conversion technology.
Project partners have developed pixel sources with 1024 independently controllable spots. For a closed emitting surface with a distance of 4.00 x 4.00 mm 0.115 x 0.115 mm and a grid size of 0.125 mm for individual pixel surfaces, these provide only 3 milliamps (lm) of only about 11 milliamps (mA). They are arranged on an active matrix IC in a 32 x 32 array, so each pixel can be individually addressed. Originally developed for automotive headlamp applications, it may also enable the fine-grained granularity required for store lighting and reading light applications.
Another major advantage is the control options, such as through the interaction between the camera and the controller. The camera acts as the "eye" of the system, capturing information about the surrounding environment and forwarding it to the controller. This "brain" processes the information and forwards the appropriately adjusted light distribution pattern to the pixels in a digital format. Each pixel can be turned on and off with different currents, more than 100,000 times per second, so it can be dimmed. Depending on the situation, the system determines which pixels are affected. In automotive applications, traffic signs (for example) will be illuminated so that the driver can see them clearly without being shocked by the glare reflected by their own headlights.
However, automotive lighting is just one of the potential areas in which intelligent selective pixel control can be applied. Options used in general lighting, such as information displays for outdoor, indoor, retail or industrial applications, are very versatile.
Optics designers face challenges and opportunities
From discrete lenses to integrated arrays, we also face significant challenges in optical design. Traditionally, illumination optics are always about blurring light sources, rather than forming images on the wall. This is also about eliminating any focus, so the spotlight emits a single, uniform, slightly divergent beam.
If we want to create an optical system that can send light from different pixels to different directions, we need to go back to the imaging system again. In optical terms, this is a simple task of converting a spatial pattern into an angular pattern.
This task is no different than when using a wide-angle ("fisheye") lens for imaging in the opposite way: it projects light from different angles to different camera pixels on the detector. It is not much different from the image projector optical system, which can direct light at different points on the image to different angles in the room.
However, the main difference is the use of LEDs as the light source, as shown in Figure 4. For camera lenses, it is not important at what angle the ray is incident on the sensor. In projectors, the light is usually pre-collimated, so the image is formed by more or less parallel rays, and the optics need only accept a limited range of angles of incidence. In addition, efficiency is not the primary goal of these systems.
The difference between the imaging camera system (left side) and the lighting system (right side) - please note the difference between the large angle aperture imaging camera system (left side) and the lighting system (right side) required for the illumination system light source - please Pay attention to the large angle aperture required for the illumination system light source
For our pixel system formed by a single LED, each pixel emits light into the entire hemisphere. Therefore, the optical device not only needs to convert the space into an angular pattern, but also needs to capture as much of the emitted light as possible - that is, the light that is emitted to the side - and orient it in the correct direction. Standard optics is absolutely impossible to achieve and requires complex optical designs with multiple relatively large lenses. Since it is still an illumination optics, the ultimate requirement for image quality is not required. However, in order to transfer the three MacAdams step distributions of the light source to the imaging area, the color correction requirements are high. Either way, a slight "blur" of the image requires hiding the structure of the LED chip in the room.
For optical designers, this is definitely a new and interesting task: combining the "two worlds" of imaging optics and illumination optics to create truly innovative solutions for space-adaptive lighting.
Competitive technology
No new technology is required to turn pixels on and off. Digital projectors with LCD and micromirror technology can be used and provide millions of pixels. However, these devices are designed to display information, not for lighting purposes. Therefore, they operate with RGB colors - this is great for displaying images, but it creates a terrible color impression when used as a source for illuminating a room. In addition, they operate by permanently creating high brightness levels and absorbing light again at pixels that should be dark. Not only is this very inefficient, but the contrast between black and white is also limited.
LED light sources are used where the pixels are illuminated only when needed, which is an energy efficient mode of the adaptive system that can be used for general illumination purposes. It also allows the design of systems with smaller heat sinks and passive cooling without fan noise.
Because the technology is extremely durable, it can also be used in harsher environments such as outdoor lighting. It can therefore be incorporated into architectural lighting or mobile devices mounted in stage and movie lights.
Artist's view of adaptive store lighting systems
in conclusion
When implementing "adaptive lighting," you can change the level of light and color temperature, as well as the distribution of light from each fixture, to actually create different lighting scenes or adapt to this situation throughout the day.
The first demonstration system based on a single LED by O researchers has been demonstrated with the "Omnipoint" system, which impressively demonstrates this concept. Since then, the miniaturization of the light source has reduced the form factor and added more and more functions. The implementation of chip-scale package (CSP) design, especially in the case of the most compact new generation of LEDs, allows for the addition of more and more pixels and planar designs. In the future, when the LED size really enters the micrometer, we will see more pixels and integrated (active matrix) design.
Multi-pixel LEDs are in the early stages of launch, offering more options for general lighting applications. This technology will take lighting to a new level as it adds another dimension to adaptive lighting: the spatial steering of light, without any moving parts, or by reducing the level of energy efficiency we use for LEDs.
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