Lighting solutions with colored LEDs provide many opportunities for illumination. One of these opportunities is to
create a color tunable light source. In this way different kinds of white light (color temperature) as well as discrete colors
may be realized. This opens the field for applications as mood lighting.
But there is always a spatial separation of the distinct LEDs that might get converted into an angular separation by any
collimating optics. This angular separation causes such problems like color fringes and colored shadows that cannot be
accepted in most applications. Conventional methods to solve these problems include e.g. mixing rods or dichroic filters.
A new approach is the use of the dispersive effect of a diffractive structure to compensate the angular separation of the
different colors.
In this contribution the potential and limitations of diffractive structures in LED color mixing applications are discussed.
Ray tracing simulations were performed to analyze such important parameters like efficiency, color performance and the
cross section of the color mixing optics. New means for the estimation of color mixing performance were developed. A
software tool makes it possible to detect the color distribution within ray trace data and it provides a quality factor to
estimate the color mixing performance. It can be shown that the spectral band width has a large influence on the mixing
process.
Ray tracing simulations are compared with results of an experimental setup such that both measured as well as simulated
data is presented.
The increasing efficiency of high power LEDs has resulted in many new applications in general lighting. To
take full advantage of the properties of LEDs, free-form surfaces can be utilized to create compact non imaging
optical systems with high efficiencies and high degrees of freedom for optical designers. One of the commonly
used methods to do optical design for this kind of systems is optimization. Appling this powerful tool allows
the enhancement of given optical elements to achieve a desired performance. In this way, free form surfaces
which are usually represented by NURBS, can be optimized and applied even close to an extended LED light
source. However, using optimization for free-form surfaces is far from being straight-forward and requires a lot of
experience mostly due to the high amount of possible optimization variables for NURBS. This comes along with
high, computational effort and difficulties concerning the choice of boundary conditions and merit functions. This
contribution presents a novel non-imaging optical design approach using the concept of free-form deformation
(FFD) in conjunction with customized optimization algorithms to create efficient optical free-form surfaces for
extended LED light sources. Within this framework, specific coordinate system transformations are used to
modify the global shape of free-form surfaces. In this way, optimization techniques relying on relatively few and
easily accessible variables can be applied successfully. All presented concepts are implemented in a flexible and
fully automated FFD optimization software tool incorporating a commercial raytracer and numerical optimization
techniques. Several examples are presented in detail and the scope of FFD based optimization is demonstrated.
KEYWORDS: Near field optics, Light emitting diodes, Geometrical optics, Light sources, Near field, Modeling, Data modeling, Optical design, Optical spheres, Ray tracing
Tailoring of secondary optics, especially in short distances to the light source, requires appropriate,
point source based, primary optic models which provide adequate accuracy. We propose a method to
generate such models for complex, even non-smooth, primary optics by using spatial radiation patterns
and applying backward tailoring. Furthermore, we demonstrate the scope of this method and the
improvements on the secondary optic design process.
Light guide rods based on multiple total internal reflections provide some powerful design opportunities. Therefore, they
are very suitable for producing arbitrary light distributions. Especially for LEDs they work highly efficient due to the use
of the whole emitted light flux and the theoretical lossless light propagation by total internal reflection. Frequent
applications are color mixing and the creation of a homogeneous luminance distribution at the output surface. However,
the capabilities of common light guide rods are under-utilized. Therefore, we demonstrate a new design approach that enhances the performance of light guiding systems and is applicable to illumination problems.
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