In lighting applications key drivers for optical design of surface textures are integration of optical elements, the disentanglement of optical functionality and appearance and late stage configuration.
We investigated excimer laser ablation as a mastering technology for micro textured surfaces, where we targeted an increase in correspondence between surface design and ablated surface for high aspect ratio structures. To achieve this we have improved the photo mask design using a heuristic algorithm that corrects for the angular dependence of the ablation process and the loss of image resolution at ablation depths that exceed the depth of field. Using this approach we have been able to demonstrate close correspondence between designed and ablated facet structures up to 75° inclination at 75 μm depth.
These facet design parameters allow for total internal reflection (TIR) as a means of beam deflection which is demonstrated in a range of mono shaped cone arrays in hexagonal tessellation. BSDF analysis was used to characterize the narrow TIR deflection beams that matched the peak positions of the design down to 28° apex. In addition, a single surface TIR-Fresnel lens design with focal distance 5 mm has been manufactured using this photo mask design algorithm and beam collimation up to 12° beam angle and 32° field angle is shown.
These outcomes demonstrate that the laser ablation process intrinsically yields sufficient small dispersion in structure and fillet radii for lighting applications.
A new method using a thin-film multilayer filter is described to couple light from high-power LEDs into a thin light
guide such as an LCD backlight. Light emitted below the critical angle is reflected back to the LED and recycled. Largeangle
emitted light passes the filter and is transported by total internal reflection in the light guide. The light guide can be
as thin as 0.3mm for an LED of 1x1mm2, and the best coupling efficiency is estimated to be around 80%. With this
approach, a backlight system can be greatly simplified but also compact collimators can be realized. In this paper the
optical design and testing of the filter is described, and a 1mm thick, 6.5mm diameter collimator is presented that emits
in a cone of 2×13°. Measurements on prototypes show good agreement with the designed characteristics.
Wall washers are applications that provide illumination effects onto a wall, generated by light sources located close to
that wall. Traditionally, incandescent and fluorescent lamps are used to generate a uniform color or a simple pattern.
Solid-state-lighting opens up the possibility to generate more complex patterns of light. In this paper, we discuss the
design and results of two different prototypes of wall washers that are able to generate a number of rows and columns of
individually addressable spots ('pixels') of light onto a wall. Our conclusions focus on the optical performance of the
chosen solutions versus the size of the optical system.
Solid State Lighting is becoming increasingly more advanced, both in terms of lumen output as well as energy
efficiency. At the same time, packages emitting enough lumens for lighting applications are decreasing in size. This
smaller packaging enables several new applications. In this paper we will discuss one of these new applications: low
cost, large, flexible and very thin light emitting surfaces. Our approach consists of using very thin transparent
lightguides. Due to their limited thickness, these lightguides are quite flexible. Tiny low power, side-emitting LEDs are
used to couple light into these lightguides. A carefully calculated outcoupling structure ensures light is coupled out
uniformly. Although this general principle is known, some aspects are new to our approach. The flexibility of our thin
lightguides can be very useful for numerous lighting applications; a radius of curvature of just a few centimeters is easily
obtained, while still maintaining good outcoupling and uniformity. Furthermore, we show that for several geometries, a
perfect homogeneous brightness can only be obtained using a precise pattern and density distribution of outcoupling
Solid State Lighting is becoming increasingly more advanced, both in terms of lumen output as well as energy efficiency. However, implementation in color consumer lighting products, such as the Philips Ambilight television sets, still requires improvements in both color reproduction as well as intensity uniformity. To build a lighting system capable of correctly reproducing a large color spectrum, 3 primary colored LEDs are required. However, this approach causes problems. In particular, the generation of a white color without color fringes is difficult to implement, as the total amount of light from each primary color should ideally be identical at each position within the light bundle. Our paper focuses on systems using a limited number of high power LEDs. The lumen output of these LEDs is such that even a single red, green and blue LED together can deliver the required lumen output for certain applications. To optimize performance for both luminance and color uniformity we investigated several design options. Ray tracing simulations are compared to the performance of real size prototypes, and recommendations are given for the design of color lighting systems.
We have built a mini-projector with LED light sources that is sufficiently small for portable applications. The projector has a three-panel architecture with transmissive LCD micro-displays in order to combine a high lumen output with a low cost price. The volume of the light engine is 100 cc.
We present a new type of optical engine for projection displays. The optical engine is based on a light guide with embedded color filters. It is intended for three-panel projection displays with micro-display panels of the transmissive type. The light guide serves the purpose of integrating the light and guiding the light to each of the three panels. Proximity illumination is used to illuminate the micro-display panels: the exits of the light guide are in close contact with the entrance of the panel. The optical design considerations underlying the principle of using light guides are discussed. Among these considerations are measures required to prevent light leakage. We also discuss light guide based optical engines relying on the principle of color recycling and polarization recycling. The results of simulations and experiments on a prototype are discussed. It is shown that the use of light guides enables a very compact design. The lumen output of such a projector can be comparable to, or even better than that of conventional systems.
In recent years, several architectures have been proposed for projection systems with an improved light efficiency by means of color recycling and/or polarization recycling. The recycling of light takes place in a rod integrator where light is coupled in from the lamp through a small hole in an entrance mirror. At the exit of the integrator, light of the wrong polarization state and/or wrong color is reflected back such that, after a round trip in the integrator, the light has a second chance of passing through the exit with a different polarization state or through a different color filter. Besides for recycling light of the wrong color or polarization, the integrator may also be used for recycling the unused light of pixels that are in a dark state. This allows for an increased brightness of bright parts in a dark scene, the so-called sparkling effect known from CRTs. We analyze the combined effects of color, polarization, and dark pixel recycling, extending the models previously proposed by Duelli et al. and by Zwanenburg.
The resolution of a low-voltage scanning electron microscope is limited by the chromatic and spherical aberration of the objective lens. Any significant improvement of the resolution requires an aberration corrector or monochromator. Recently, correction of both Cc and Cs has been demonstrated in a SEM, using a combination of magnetic and electrostatic quadruples and octuples. This paper presents an alternative and purely electrostatic design which, like most quadrupole-octuple correctors, is based on the concept of creating a stigmatic path and correcting Cc in the two line foci. We propose a combination of strongly oscillating mono- and quadruple fields as dispersive elements. Our arrangement of the mono- and quadruple fields creates a thick non-focusing correcting elements, which corrects for Cc in one plane, while these fields act as a telescope (with magnification M=+/- 1) in the other plane. The telescopic properties of the correcting element in both planes reduce the chromatic magnification aberration of the corrector to acceptable proportions. To model our corrector realistically, the electrostatic potential has been computed for a 3D electron geometry with the EO-3D package from MEBS. From this the electrostatic potential has been computed for a 3D electrode geometry with the EO-3D package from MEBS. From this potential we extracted axial field functions for the monopole up to octuple fields. Ray tracing with these axial fields using MEBS's MULTIPOL package yields all aberrations up to fifth order. The numerical calculations show a resolution enhancement by a factor of 2 with a Cc and Cs corrector that is based on our novel correcting elements.