The advance of technology continuously enables new luminaire designs and concepts. Evaluating such designs has
traditionally been done using actual prototypes, in a real environment. The iterations needed to build, verify, and
improve luminaire designs incur substantial costs and slow down the design process. A more attractive way is to evaluate
designs using simulations, as they can be made cheaper and quicker for a wider variety of prototypes. However, the
value of such simulations is determined by how closely they predict the outcome of actual perception experiments.
In this paper, we discuss an actual perception experiment including several lighting settings in a normal office
environment. The same office environment also has been modeled using different software tools, and photo-realistic
renderings have been created of these models. These renderings were subsequently processed using various tonemapping
operators in preparation for display. The total imaging chain can be considered a simulation setup, and we have
executed several perception experiments on different setups. Our real interest is in finding which imaging chain gives us
the best result, or in other words, which of them yields the closest match between virtual and real experiment.
To answer this question, first of all an answer has to be found to the question, "which simulation setup matches the real
world best?" As there is no unique, widely accepted measure to describe the performance of a certain setup, we consider
a number of options and discuss the reasoning behind them along with their advantages and disadvantages.
In the design of professional luminaires, improving visibility has always been a core target. Recently, it has become
clearer that especially for consumer lighting, generating an appropriate atmosphere and pleasant feeling is of almost
equal importance. In recent studies it has been shown that the perception of an atmosphere can be described by four
variables: cosiness, liveliness, tenseness, and detachment. In this paper we compare the perception of these lighting
characteristics when viewed in reality with the perception when viewing a simulated picture. Replacing reality by a
picture on a computer screen such as an LCD monitor, or a piece of paper, introduces several differences. These include
a reduced dynamic range, reduced maximum brightness and quantization noise in the brightness levels, but also in a
different viewing angle, and a different adaption of the human visual system. Research has been done before to compare
simulations with photographs, and simulations with reality. These studies have focused on 'physical variables', such as
brightness and sharpness, but also on naturalness and realism. We focus on the accuracy of a simulation for the
prediction of the actual goal of a lot of luminaires: atmosphere creation. We investigate the correlation between
perceptual characteristics of the atmosphere of a real-world scene and a simulated image of it. The results show that for
all 4 tested atmosphere words similar main effects and similar trends (over color temperature, fixtures, intensities) can be
found in both the real life experiments and the simulation experiments. This implies that it is possible to use simulations
on a screen or printout for the evaluation of atmosphere 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.
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.
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.