Volume 8, Issue 1 - Illumination optics / Guest Editors: Tran Quoc Khanh, Cornelius Neumann

In illumination optics, color mixing is a key design task, but the realization can be a challenge. While tunable light sources based on multiple LEDs are commonplace, color homogenization is just as important for white LEDs, due to their spatial and angular color variation. In this tutorial, we first look at color mixing from an abstract, phase space-based viewpoint. From there, we derive a taxonomy of color mixing problems: How is the multi-color light source composed? What kind of homogeneity is required in the target? How is the homogenization influenced by source and target étendue? We categorize these problems and we present a toolbox: A selection of optical design elements, e.g. mixing rods and fly’s eye arrays, and we show for each design pattern how it fits into the taxonomy.

High-resolution vehicle headlamps are the technological way to intelligently illuminate the traffic area to increase safety and comfort. For the technical realization of these headlamps, different technologies come into question, which are the subject of intensive research at universities and among the manufacturers. We present an overview of the possible technologies and analyze their potential for use in high-resolution headlamps. Furthermore, we explain how the design of the optical system for the different technologies can be made. Another part of this paper is the comparison of published prototypes of high-resolution headlamps and the compilation of key properties.

The reproduction of glare scenarios in driving simulators is restricted by the limitations of conventional projector and display technology. In existing solutions, light sources are usually added to the optical path by combining common simulator technology with, for example, grids based on light-emitting diodes (LED). In this article, we introduce a new way to simulate glare sources on a common driving simulator back-projection screen using an additional projector and an additional reflective screen. In a first attempt, a concept with retroreflective sheets is proposed, and the requirements and current limitations of this setup are shown. Further development of the concept leads to an attempt with holographic diffusers. With an experimental setup based on the second concept, we aim to assess its feasibility, evaluate current challenges, and outline future requirements. The results show that it is possible to simulate a static glare scenario with correct geometrical conditions and headlights with luminances of about 100 000 cd/m 2 . Current limitations are an unbalanced color efficiency, the size and cost of available diffusers, and the black-level values and in-picture contrast of the used projector that cause an outshining of the environmental simulation.

This paper summarizes selected approaches, to generate spectral ray data for different types of spectrally varying light sources including only angular variable as well as spatial and angular variable sources. This includes a description of their general ideas and applications, the required measurements, and their mathematical concepts. Finally, achieved results for an Red/Green/Blue/White-light emitting diode (RGBW-LED) system are shown. Ray tracing simulations of a spatially and angularly spectral varying LED system combined with a spectrally sensitive optical system are qualitatively and quantitatively compared to a colorimetric far-field measurement of the same system. The results demonstrate the potential and benefits of spectral ray files in general.

This article gives an insight into the theory and application of photobiological safety assessment. To illustrate several aspects of this topic, the project ‘Measurement and assessment of optical radiation sources, relevant to the general population – Risk estimation to the eye, especially blue light hazard and glare’ by the German Federal Office for Radiation Protection, where 40 different products were measured and assessed, is used as an exemplary case. Products were chosen which were promoted to have a high output intensity and which are available to the public. Most of the products with incoherent radiation were classified in risk group 2 according to DIN EN 62471:2009 [DIN EN 62471:2009 – ‘Photobiologische Sicherheit von Lampen und Lampensystemen’]. Only a few of them were labeled correctly or had the right warning notice. Additionally, to the results of this market survey, practical aspects of the hazard measurement and assessment are emphasized.

Various sensors in nowadays cars are already used to assist the driver or to inform him through several display technologies. However, some information cannot properly be displayed through conventional systems. This article shows the development of an assistance system through projections on the road beginning from human perception and interpretation of different symbols. The results of a simulator study are displayed, where test subjects had to state how they intended to react when seeing certain symbols on the road and how they interpreted these signs. As most promising symbols for all possible actions, two parallel lines were used in a further dynamic field study. The outcome of this study is presented and discussed. Having additional information about the car width displayed on the road, drivers managed challenging situations better without being distracted. Projections on the road showed a big potential of being used in broad traffic as assistance systems.