Modern Automotive headlamps enable improved functionality for more driving comfort and safety. Matrix or Pixel light
headlamps are not restricted to either pure low beam functionality or pure high beam. Light in direction of oncoming
traffic is selectively switched of, potential hazard can be marked via an isolated beam and the illumination on the road
can even follow a bend. The optical architectures that enable these advanced functionalities are diverse.
Electromechanical shutters and lens units moved by electric motors were the first ways to realize these systems.
Switching multiple LED light sources is a more elegant and mechanically robust solution. While many basic
functionalities can already be realized with a limited number of LEDs, an increasing number of pixels will lead to more
driving comfort and better visibility. The required optical system needs not only to generate a desired beam distribution
with a high angular dynamic, but also needs to guarantee minimal stray light and cross talk between the different pixels.
The direct projection of the LED array via a lens is a simple but not very efficient optical system. We discuss different
optical elements for pre-collimating the light with minimal cross talk and improved contrast between neighboring pixels.
Depending on the selected optical system, we derive the basic light source requirements: luminance, surface area,
contrast, flux and color homogeneity.
Free form surfaces allow elegant solutions in illumination optics. A complex function of the system can be achieved by a single optical element. Free form elements are usually manufactured by reproduction techniques, such as injection moulding of plastic. Manufacturing tolerances are crucial to maintain the required function while at the same time yielding the lowest possible price. We implemented a Monte Carlo tolerancing method for illumination systems. Tolerances include shape deviations of optical elements and assembly tolerances. In the absence of standards for free form tolerances and illumination optics tolerancing, communication between optics design, manufacturing and testing is often inefficient. In order to enable a highly automated evaluation of part measurement data to assess compliance with tolerances, we developed an approach to combine information from optics design, mechanical construction, manufacturing and testing into one continuous data chain. The research project is granted by the German Ministry of Education and Research.
Technical luminaries have to compete on an economic basis. Optics design plays a key role for the
development of efficient products, providing unique light distributions and minimizing the total costs of
Applications requiring high lumen packages are traditional the domain of light sources like discharge lamps. Currently,
LEDs make their way into such applications. LED street lighting projects, which are regularly covered in the press,
provide a case of point.
Life time and luminous efficacy are considered as being the main advantages of LEDs. Nonetheless, other current light
sources for street lighting have similar performance. Analysing a street-lamp as a complete system, we can show that
LED solutions have significant advantages if highly efficient optics are used. We present an example with tailored free-form
optics. These make efficient use of the valuable LED light by exactly redistributing it into the desired illuminance
Due to antiquated technologies (calculation methods, regulations, lighting and luminaire concepts, production techniques) current outdoor lighting causes a lot of problems like light pollution, glare, energy waste etc.
New types of luminaires, and in consequence new outdoor lighting concepts, can be created by combining advanced calculation methods for optical surfaces with recent production technologies and novel light sources such as short arc metal halide lamps. Light emitted from this small Etendue light sources can precisely be redirected by 3D-curved surfaces manufactured with injection molding, milling and aluminium metallization. The required optical design may use techniques like complex surface calculations and 3D-Tailoring.
An innovative concept based on the latest findings in visual perception research is to focus the light of such short arc light sources onto a facetted secondary mirror which provides the desired illuminance distribution on a facade or a public place. These systems are designed to fulfill lighting requirements as well as providing visual comfort. Thus lamps with improved color rendering, luminous efficacy and increased lifetime are used and glare is minimized by splitting the reflector into many facets (light spot decomposition).
A few examples of realized projects will be presented where such complex facetted surfaces are used to reach a special quality of light. Using novel techniques like 3D-Tailoring, each facet can be designed to individually create the desired (e.g. uniform) illuminance distribution on the target surface - in this case, a large facade. For this particular application, we chose to impose a square boundary for each facet, in order to tile the rectangular aperture of the secondary mirror without compromising efficiency.
3-D tailoring is a constructive method for the design of free-form optical elements for illumination. The light of a point source is redirected in a controlled manner to cast a prescribed irradiation pattern on a target surface. Free parameters can be used to control the shape of the surface resulting from the tailoring process. Every change in the parameters may lead to an entirely different design. Hence the choice of parameters is crucial for the technical feasibility and the visual appearance of the luminaire. Examples of free parameters are the chosen caustics, trimming of the surface, the choice between mirror and lens optics, and the mutual orientation of source and optical elements.
Compound parabolic concentrators (CPCs) are good candidates for secondary concentrators in solar applications. Practical considerations, however, sometimes dictate the use of planar as opposed to curved reflectors. In addition polygonal apertures may be desired in order to tile a large area with several smaller secondary concentrators. We analyze in our contribution secondary concentrators which approximate a CPC but consist of plane facets with various numbers of subdivisions in axial and circumferential direction. We found that an `intuitive' axial profile with a constant angle between neighboring facets does not lead to optimal performance. We optimized by ray-tracing the size and orientation of the facets and found concentrators with significantly higher performance as compared to the `intuitively' facetted CPCs. The resulting shapes are usually significantly longer than classical CPCs. The higher the reflectivity of the surfaces, the longer the optimized concentrators get, approaching the infinite cone as an ideal concentrator for perfect reflectivity.
In solar tower plants, where a rotationally symmetric field of heliostats surrounds the tower, an axisymmetric secondary concentrator such as a Compound Parabolic Concentrator (CPC) or a tailored concentrator or a cone is the obvious choice. For locations at higher latitudes, however, the reflecting area of the heliostats may be used more efficiently if the field of heliostats is located opposite to the sun as seen from the tower. Then the field is asymmetric with regard to the tower. In the case of an asymmetric field, an axisymmetric concentrator necessarily has a concentration significantly lower than the upper limit. Furthermore, the area on the ground from which a tilted axisymmetric concentrator accepts radiation is an ellipse, including also heliostats very distant to the tower producing a large image of the sun. Therefore we investigate asymmetric secondaries. From the shape of the edge ray reflectors constructed for rays in the central south-north plane we conclude that a skew cone reflector might be appropriate for the field and optimized its free parameters by means of raytracing. Asymmetric concentrators may increase the concentration by up to 25% at the same efficiency compared to optimized axisymmetric CPC or cone reflectors.