Illumination Optics VIII

Quantities emerge in science and engineering when enough persons recognize its importance, and agree on concise, meaningful and unique names and symbols. Such quantities allow precise, effective communication and clarify our thinking. In illumination optics, the quantity "refractive index squared times projected solid angle" forms one half of the definition of etendue. It is also conserved before and after refraction at an infinitesimal surface element. We propose: “Angular extent X”: concise, conveying immediate meaning, and not in use yet. Differential etendue becomes dU = dA dX. In many important simple cases, etendue itself is simply U = A X. Moreover, for constant luminance L, illuminance E is simply E = L X. Thus, in imaging optics, relative illumination on a sensor is proportional to X, including all pupil aberrations.

Designing compact freeform optics for extended light sources requires explicit treatment of the source extent in both space and angle, where point-source formulations are no longer valid. We present a new direct design method for this problem. The method establishes a mathematical framework in which extended-source freeform design is cast as a coupled Monge--Amp\`ere system with a nonlinear boundary condition. The extended source is discretized into subsources, and the irradiance contribution of each subsource is evaluated deterministically, so the freeform surface is obtained directly from the numerical solution without Monte Carlo ray tracing or optimization-based design loops. The formulation is examined in single-source on-axis, single-source off-axis, and array-source configurations. In all three cases, the computed irradiance patterns reproduce the prescribed target structures.

Designing freeform optics for finite-étendue sources is challenging, as most methods assume ideal, zero-étendue sources. While this simplifies calculations, the performance degrades with real sources. We introduce a deep learning method to predict freeform surfaces directly. The trained model learns the entire solution space, enabling prediction of freeform surfaces for unseen source-target combinations. This represents the first generalizable deep learning framework for nonimaging freeform design and is a first step toward data-driven methods for finite-étendue illumination systems.

We present the design and the fabrication of a high-power illumination module comprising 30 LEDs, each coupled to a dedicated pyramidal collimator and to a lens, for a total power of more than 1.5kW. When installed on an existing solar concentrator, this artificial light source provides additional energy for illuminating a photochemical reactor in which hydrogen is combined with CO2 to produce green methanol, allowing to run the process also when solar energy is not available. We discuss the design of the artificial light source and show how a system made of flat mirrors and commercial lenses meets the power and irradiance specifications.

No, this is not a typo. Pocus is a third order effect such as the Seidel aberrations. The difference is that it does not affect the image but changes the angles of incidence for revery image location. We may consider pocus as a kind of a field dependent pupil. The purpose of this contribution is to provide an optical design that allows for to modify the intensity distribution at the exit of a fiber or lightguide within the range supported by the numerical aperture of the fiber. For this purpose, we remember that a skew incidence of a light beam to a fiber would increase the angular extent. We realize this with an optical system that images the surface of an LED to the fiber entrance area but allows for a suitable pocus modification and this way a tunable angulsr distribution. There is a wide variety of applications conceivable in the technical and medical fields.

Display backlights typically rely on phosphor-converted white LEDs whose broad emission spectrum limits efficiency and color-saturation. Quantum dots (QDs), owing to their narrow emission bandwidths and high photoluminescent quantum yields, offer a promising alternative when excited by blue LEDs. Current QD implementations involve a QD-polymer film positioned above a lightguide illuminated by blue LEDs. This approach requires a large quantity of QDs and provides modest efficiency gains. In this work, ray-tracing simulations are used to design and optimize a side-lit lightguide integrating spatially patterned red, green, and scattering microstructures directly on its surface, which can be realized using inkjet-printing techniques. An iterative two-stage algorithm optimizes luminance and color uniformity by coupling light extraction and color conversion. Simulation results show that the patterned QD lightguides achieve high luminance and color uniformity while significantly reducing QD usage compared to conventional film-based designs, enabling efficient and spectrally tailored backlights for next-generation displays.

Conventionally, the optical design of a low-beam headlamp is more complex than that of general lighting systems due to the requirement of producing a high-contrast cut-off line. In this report, we present a simple yet robust design approach for bicycle low-beam headlamps using a cylindrical lens array (CLA), or lenticular lens, in combination with reflective optics. First, a reflector is employed to generate a beam with a triangular or trapezoidal intensity profile—wide at the top and narrow at the bottom. The CLA then reshapes this beam by horizontally stretching it to achieve the desired light distribution. Based on this method, we design and fabricate an LED headlamp that satisfies two vehicle headlamp regulations (K-mark and ECE R113). The proposed optical design is inherently robust, delivering a smooth and uniform light pattern while effectively mitigating artifacts and quality degradation caused by reflector fabrication errors and surface discontinuities in multi-segment designs.

Displays, backlit symbols, or ambient lighting applications often require getting large surfaces backlighted in a homogeneous way. This article will present a LucidShape CAA V5 Based integrated feature to design and simulate micro-elements, or 3D Texture, as a mesh. This way, hundreds of thousands of elements, either bumps or holes, can be integrated into light plates. Monte-Carlo simulation of such a mesh surface is much faster than a pattern geometry modeling. An optimization of the size of each element will be presented on a curved display example, to obtain a homogenous display illumination. Finally, the article will show a macro for loading elements following a grayscale image: elements’ size will follow the grayscale level of each pixel, thus permit simulating a backlit logo.

The 20th and early 21st centuries have seen significant growth in the physical size and complexity of astronomical land-based telescopes. These scale increases, combined with tighter image-quality requirements arising from a combination of scientific demands and improvements in technology, have led to the development of active optics for telescope control, where wavefront sensors combine with actuators to drive the shape and position of optics in closed loop, correcting for deflections caused by gravity orientation and temperature changes. Active optics for large telescopes was conceived and developed in the late 1970s, 1980s, and 1990s, and, arguably, only brought to full maturity in the early 2000s. At this point in time, we stand poised on the brink of the Extremely Large Telescope (ELT) era, where apertures in the 10 m range from the 1990s generation of optical–infrared telescopes have leaped by factors of two to four in the upcoming generation of telescopes. At this scale, optical flexures and deflections are amplified compared to the current generation of telescopes, and the combination of open-loop modelling for initial optics positions and shapes, and wavefront sensing for closed-loop control and convergence, is seriously challenged. Since the late 2000s, a new approach, based on the direct metrology of optical components and instrument interfaces, has been developed. Direct metrology offers an interesting intermediate alignment stage between open-loop modelling of positions and closed-loop wavefront sensing. This paper discusses the development and application of these approaches to a range of large telescopes, including optical and radio telescopes.

This presentation will provide a comprehensive overview of European Space Agency (ESA) ongoing efforts to prepare for the next generation of optical Earth Observation missions. First, we will present the science-driven Earth Explorers and Scout missions addressing key scientific issues, followed by an update on preparations for future Meteorology and Copernicus missions. Second, we will present the pre-development activities of innovative instrumental concepts and associated technologies engaged to prepare the future of Earth Observation optical missions. Finally, we will highlight the activities focused on the preparation of compact optical payloads for small satellites.

Optical designs commonly combine an Illumination subsystem and an imaging subsystem. In some cases the two subsystems can be designed separately, but then the combination needs to be traced to simulation the final product. The combination has both accuracy and performance issues that need to be considered. We will explore how this combination impacts the ray trace through interesting examples.

Adapting to rapidly evolving design requirements and user feedback is crucial across many design industries. This paper presents a hybrid approach that integrates pySpeos, a Python-based optical simulation tool with SimAI, an AI model trained on legacy engineering data, to enable rapid and accessible lighting analysis. The method significantly reduces simulation time—by up to 80%—while maintaining high visual accuracy. By generating lighting maps through AI prediction and post-processing, the system minimizes the need for expert knowledge as well as allowing faster decision-making for early-stage design evaluations and Request for Quotation processes.

Solar focus effects occur when sunlight enters a vehicle’s headlamp at specific orientations, concentrating energy onto sensitive components and causing thermal damage or deformation. These events often arise when vehicles are parked on slopes or exposed to direct sunlight for extended periods. This presentation introduces an automated workflow for predicting and mitigating such risks during the optical design stage. By combining parametric simulation, angular sweeps, and automated irradiance analysis, the method efficiently identifies high-risk geometries and sun-angle conditions without extensive manual post-processing. Simulation based studies on reflector-based lamps demonstrate how this approach improves accuracy, reduces analysis time, and supports integration with thermal validation for comprehensive solar-load assessment.

Infrared heating powered by renewable energy sources is a promising alternative to replace fossil fuels in the curing processes for industrial powder coatings, Infrared lamps illuminating the sample inside a reflective oven can be individually regulated to generate a homogeneous irradiance distribution on the samples surface, thus allowing to significantly reduce pre-heating and dwell times. As a first step for the layout of an industrial IR-curing line process, it is required to identify the crucial performance parameters and understand their interaction with varying product shapes and coatings. To achieve this, optical simulations of the irradiance surface distribution in a prototype IR-furnace are performed for different illumination setups, followed by thermal simulations with the irradiance distributions as input. To demonstrate feasibility, the parameters of the optical and thermal simulation model were selected in such a way as to produce a model that was as simple as possible, yet still matched the measured temperature distribution in the prototype IR furnace system.

Phase space optics is a powerful way to visualize illumination systems, where complex irradiance patterns arise from relatively simple phase space transformations. However, the full optical phase-space is four-dimensional and difficult to visualize, limiting the applicability to 2D optical systems. In this talk, we will present a direct phase-space simulation method that models light sources in phase-space as a sum of Gaussian radiance distributions, and traces these radiance distributions through the optical system to capture the underlying phase-space transformation. The approach extends naturally to 3D optical systems, and projects directly onto the target plane to deliver high-resolution irradiance estimates without requiring dense Monte Carlo sampling. We show through simple design-examples how this permits rapid simulation and gradient-based optimization of freeform optical surfaces, and also demonstrate how algorithms from machine learning like Gaussian splatting and backpropagation can be adapted to run these phase-space simulations rapidly and differentiably on the GPU.

LED-based illumination has become increasingly attractive for spectroscopy, imaging, and sensing applications thanks to their spectral diversity and compactness. However, efficiently combining the emission from multiple LEDs into a single, well-defined output remains a major optical design challenge. The overlap of multiple LED sources often leads to significant étendue mismatch, non-uniform illumination, and reduced optical efficiency. We present an overview of recent advances in the optical design of multi-LED systems, from state-of-the-art methodologies to a novel compact illumination architecture employing a single freeform mirror to collect and combine the LED emission beams. Particular attention is given to the role of the freeform mirror to spatially and angularly merge different LED channels, alongside an evaluation of the system’s optical efficiency, compactness, spectral homogeneity, and robustness. This design performance is supported by experimental validation within a proof-of-concept demonstration, paving the way towards its implementation in spectroscopic sensing applications.

The design of optics has seen very significant advances over the last seven decades or so, a lot of which has been due to the tremendous increase in the power of computing & software. In 1675, Isaac Newton said that “If I have seen further, it is by standing on the shoulders of giants”. The same is true of the optical designers of my generation in that we have benefitted so much from the work of the “giants” of previous generations. The presentation will therefore include brief synopses of the contributions of a few of these giants. Some selected examples will be given of the advances over the computer age in the means of designing optics and also the developments in specific optical devices. The presentation will be dedicated to the memory of John Greivenkamp, a great educator in optics, who was to have been its joint author.

This study presents the design and characterization of a single-molecule white-light emitter for organic light-emitting diode (OLEDs) as an alternative to conventional RGB-based white OLEDs (WOLED), which often suffer from excitonic imbalance and interfacial quenching. The solid sample of the synthesized compound exhibits dual emission arising from distinct excited-state processes. The high-energy blue emission is from an intramolecular charge-transfer state, and the low-energy yellow emission is from excimer formed due to intermolecular interactions. The compound displays high glass-transition and melting temperatures. Time-dependent density functional theory calculations using the optimally tuned ω*B97XD functional provided insight into monomeric and excimer excited-state wavefunctions. The emitter was implemented for a host-free WOLED and, under reduced intermolecular interactions, for blue OLED, demonstrating its versatile applicability. Acknowledgement: The Research Council of Lithuania (LMTLT) is acknowledged for the funding, contract No. P-DAK-26-1.

Organic emitters exhibiting thermally activated delayed fluorescence (TADF) have emerged as promising alternatives to phosphorescent metal complexes in organic light-emitting diodes (OLEDs). Purely organic TADF materials offer low cost and high efficiency, yet achieving specific emission colors and optimal device performance remains an active challenge. In this work, new pyrido[2,3-b]pyrazine derivatives linked via phenyl bridges to carbazole or phenothiazine groups were investigated. Their photophysical properties, including absorption, emission, photoluminescence quantum yields, excited-state lifetimes, and singlet–triplet energy gaps (ΔEST), were characterized. The compounds exhibited efficient TADF with ΔEST values as low as 0.16 eV and emission ranging from green to orange, with quantum yields up to 82 %. OLEDs employing these emitters achieved an external quantum efficiency (EQE) of 0.94 % in neat films, which increased to 21.3 % in optimized host–guest systems, demonstrating excellent performance near the theoretical limit for TADF-based devices. Acknowledgment: Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Innovation Council and SMEs Executive Agency (EISMEA). Neither the European Union nor the granting authority can be held responsible for them. (SCOLED, Grant Agreement No. 101098813)

Infrared illumination powered by renewable energy sources can replace conventional heating based on fossil fuels. The use of infrared radiation as a heat source for industrial powder coating systems also provides a very fast and direct heating of the coating materials. Nevertheless, the difficulty of an evenly distributed illumination for industrial products with different shapes prevented this technology from a widespread use so far. Innovative approaches need to be pursued for the intended use of infrared heating in industrial powder coating processes. The prototype infrared furnace in our laboratory with highly reflective walls and a special octagonal design facilitates a largely homogeneous illumination even of geometrically complex products. An infrared camera visualizes temperature profiles of white and black coating samples during the heating process. The subsequent comparison of the experimental results with corresponding simulations will deliver the basis for the layout of future industrial facilities.