Volume 5, Issue 2 - Illumination optics / Guest Editor: Cornelius Neumann

The following article shall describe how human vision by night can be influenced. At first, front lighting systems that are already available on the market will be described, followed by their analysis with respect to the positive effects on traffic safety. Furthermore, how traffic safety by night can be increased since the introduction of high resolution headlamps shall be discussed.

Signal functions have to fulfill statutory regulations such as ECE or FMVSS108 to provide a clear signal to other road users and satisfy the same standard definitions of lighting parameters. However, as rear combination lamps are very different from one another, and these days are an increasingly powerful design element of cars, automotive manufacturers want an innovative, superior, and contrasting design. Daytime appearances with a new and unusual look and nighttime appearances with unexpected illumination are strong drivers for developing amazing innovative signal functions. The combination of LED technology and different forms of light-guiding optics, new interpretations of common optical systems to develop various styling options, the use of new materials and components for lighting effects, the introduction of OLED technology on the automotive market, and amazing new optical systems, using diffractive or holographic optics in future rear lamps, are paving the way for further, exciting design possibilities. The challenge of new signal functions is to take these possibilities and to develop the appearance and illumination effects the designer wants to reinforce the image of the car manufacturer and to fit harmoniously into the vehicle design. Lighting systems with a three-dimensional design and appearance when unlit and lit, amazing 3D effects, and surprising lighting scenarios will gain in importance. But the signal lights on cars will, in the future, be not only lighting functions in rear lamps; new functions and stylistic illuminations for coming/leaving-home scenarios will support and complete the car’s overall lighting appearance. This paper describes current lighting systems realizing the styling requirements and future lighting systems offering new design possibilities and developing further stylistic, visual effects and improved technologies.

In many illumination problems, the beam pattern needed and/or some geometrical constraints lead to very asymmetric design conditions. These asymmetries have been solved in the past by means of arrangements of rotationally symmetric or linear lamps aimed in different directions whose patterns overlap to provide the asymmetric prescriptions or by splitting one single lamp into several sections, each one providing a part of the pattern. The development of new design methods yielding smooth continuous free-form optical surfaces to solve these challenging design problems, combined with the proper CAD modeling tools plus the development of multiple axes diamond turn machines, give birth to a new generation of optics. These are able to offer the performance and other advanced features, such as efficiency, compactness, or aesthetical advantages, and can be manufactured at low cost by injection molding. This paper presents two examples of devices with free-form optical surfaces, a camera flash, and a car headlamp.

Total internal reflection (TIR) collimators are essential illumination components providing high efficiency and uniformity in a compact geometry. Various illumination design methods have been developed for designing such collimators, including tailoring methods, design via optimization, the mapping and feedback method, and the simultaneous multiple surface (SMS) method. This paper provides an overview of the different methods and compares the performance of the methods along with their advantages and their limitations.

The introduction of adaptive front lighting systems for vehicles has increased road safety and drivers’ comfort significantly within the last years. A next step in this development is the realization of higher resolution systems to further increase the functionality of vehicle headlamps toward fully adaptive front lighting systems. In this paper, we present a short overview on highly dynamic front lighting systems and the essential technologies for their realization. Different approaches are compared and evaluated regarding their applications for headlamp systems. As an example for on-road projection systems, a laser-based scanning unit is set up and evaluated.

For mixing light from different colored LEDs, an optical color mixing system is required to avoid colored shadows and color fringes. Concerning the different color mixing systems, mixing rods are widespread as they provide very good spatial color mixing with high efficiency. The essential disadvantage of mixing rods, so far, is the lack of angular color mixing. The solution presented in this publication is the application of a chaotic-dispersive billiard’s geometry on the cross section of the mixing rod. To show both the spatial and the angular mixing properties of a square and a chaotic-dispersive mixing rod, simulations generated by the raytracing software ASAP are provided. All results are validated with prototype measurements.

This paper presents a dual-mode spectral imaging system, which allows switching between pure lateral imaging and the spectrally resolved recording of spatial information. The optical system was equipped with tunable functionalities in order to achieve high flexibility, cover a wide range of object distances, and address extended field angles. A fluidic membrane lens was used for the variable focus, and the recording of the laterally extended scene was made possible by successively adjusting the different tilting angles to the different object positions. The capability and performance of the spectral imaging system were assessed using various test scenes, with different aimed field positions and changing object distances.

A digital holographic system is used to image the plume dynamics of a train of picosecond laser pulses interacting with titanium, aluminium, copper and brass. The recorded process dynamics are used to propose two optimisation strategies: first, by observing the time at which the plume fully dissipates and, second, through calculation of the minimum beam displacement required to maximise energy delivery to the sample by avoiding the plume. The proposed approach could further be applied in real industrial process design, allowing laser users to formulate a processing strategy based on process dynamics rather than lengthy post-process evaluation of a sample.