High-resolution vehicle headlamps represent a future-oriented technology that can be used to increase traffic safety and driving comfort. Typically, selective absorbing of light using a spatial modulator like DMD, LCD or LCoS creates the light distribution of such headlamp systems. A similar effect can be generated by using LED arrays. Its additive principle generates light only in specific segments if necessary. In general, these arrays can be distinguished between conventional LEDs arranged in an array and micro pixel LEDs. Conventional LED arrays characterize by the design (THT or SMD) with typically a few millimeters edge length. In contrast, a micro-pixel LED uses COB technology, in which individual LED dies are packed in a single housing directly next to each other at a distance of a few microns. By increasing the array resolution, the challenges in designing an optical system for high-resolution headlamps rise. High efficiencies and contrasts call for small, accurate lens geometries and negligibly scattered light effects. Due to limited installation space and manufacturing tolerances, compromises have to be made. Ideally, the optics have to be accurate enough to image each pixel of the micro LED with high contrasts and high efficiency and still be too blurry to project the gaps between each pixel. This results in small distances between LED and optics and therefore in diffcult to manufacture radii of curvature. In this paper we specify the challenges to implement micro pixel LEDs in headlamp systems, as well as present the controllability of scattered light effects of these systems.
Glare avoidance and marking lights are two of the many functionalities offered by advanced automotive headlamps such as Matrix-LED systems. DMD-based headlamps offer resolution enhancements to these two adaptive lighting functionalities. This is achieved via a precise optical system that exhibits high marking and glare avoidance efficiencies. This work evaluates two concepts for an optical system that enables fully adaptive light distributions.
Light distributions from automotive headlamps are characterized by a wide aspect ratio and a centrally located hotspot marked by a high luminous intensity. Due to the popular use of DMDs in video projectors, DMD properties counter-productive to automotive applications are regularly encountered. For example, DMDs for projectors require to be illuminated homogeneously in order to obtain a homogeneous projection whereas headlamps require a hotspot centric distribution. It is possible to digitally create a hotspot with conventional projection optics but the results come with a significant loss in optical efficiency.
The two concepts for an optical system compared in this paper are: anamorphic optics and optics with pincushion distortion. This comparison is conducted using optical simulations. Photometric measurements are then taken from a vehicle headlamp based DMD and distorting optics and compared with the simulation as a validation step. Due to the strong distortion of the lens system the relation between the DMD image and the final light distribution is highly non-linear. The paper is concluded with key observations with regards to this non-linearity.
Bright white light sources are of significant importance for automotive front lighting systems. Today’s upper class vehicles mainly use HID or LED as light source. As a further step in this development laser diode based systems offer high luminance, efficiency and allow the realization of new styling concepts and new dynamic lighting functions. These white laser diode systems can either be realized by mixing different spectral sources or by combining diodes with specific phosphors. Based on the approach of generating light using a laser and remote phosphor, lighting modules are manufactured. Four blue laser diodes (450 nm) are used to activate a phosphor coating and thus to achieve white light. A segmented paraboloid reflector generates the desired light distribution for an additional car headlamp. We use high speed milling and selective laser melting to build the reflector system for this lighting module. We compare the spectral reflection grade of these materials. Furthermore the generated modules are analyzed regarding their efficiency and light distribution. The use of Rapid Prototyping technologies allows an early validation of the chosen concept and is supposed to reduce cost and time in the product development process significantly. Therefor we discuss costs and times of the applied manufacturing technologies.
Bright white light sources are of significant importance for automotive front lighting systems. Today’s upper class
systems mainly use HID or LED light sources. As a further step laser diode based systems offer a high luminance,
efficiency and allow the realization of new dynamic and adaptive light functions and styling concepts.
The use of white laser diode systems in automotive applications is still limited to laboratories and prototypes even
though announcements of laser based front lighting systems have been made. But the environment conditions for
vehicles and other industry sectors differ from laboratory conditions. Therefor a model of the system’s thermal behavior
is set up.
The power loss of a laser diode is transported as thermal flux from the junction layer to the diode’s case and on to the
environment. Therefor its optical power is limited by the maximum junction temperature (for blue diodes typically
125 - 150 °C), the environment temperature and the diode’s packaging with its thermal resistances. In a car’s headlamp
the environment temperature can reach up to 80 °C. While the difference between allowed case temperature and
environment temperature is getting small or negative the relevant heat flux also becomes small or negative. In early
stages of LED development similar challenges had to be solved. Adapting LED packages to the conditions in a vehicle
environment lead to today’s efficient and bright headlights. In this paper the need to transfer these results to laser diodes
is shown by calculating the diodes lifetimes based on the presented model.