William J. Cassarly

Fast freeform reflector generation using source-target maps

We propose a freeform reflector design method based on the mapping of equi-flux grids between a point source and a target. This method imposes no restriction on the target distribution, the reflector collection angle or the source intensity pattern. Source-target maps are generated from a small number of target points using the Oliker algorithm. Such maps satisfy the surface integrability condition and can thus be used to quickly generate reflectors that produce continuous illuminance distributions.

Designing freeform reflectors for extended sources

We propose a design method for single reflectors that takes into account extended sources with any arbitrary luminance distribution. This method is suitable for non-uniform prescribed illuminance distributions with arbitrary shapes. We use the method of supporting ellipsoids developed by Oliker in conjunction with optimization in order to control the effects of the source extent. Design examples related to street illumination and LED illumination are presented.

Observations on the linear programming formulation of the single reflector design problem.

We implemented the linear programming approach proposed by Oliker and by Wang to solve the single reflector problem for a point source and a far-field target. The algorithm was shown to produce solutions that aim the input rays at the intersections between neighboring reflectors. This feature makes it possible to obtain the same reflector with a low number of rays - of the order of the number of targets - as with a high number of rays, greatly reducing the computation complexity of the problem.

Optimization for illumination systems: the next level of design

Computers are routinely used to design illumination systems. Automating the design process is enhanced through the use of optimization procedures. This paper describes some of the underlying illumination optimization fundamentals: parameterization, merit functions, and optimization algorithms. Numerous interesting examples of illumination design problems that benefit from optimization are shown. These examples illustrate illumination optimization through use of ray aiming, computing illuminance using flux tubes, and computing illuminance using Monte Carlo simulations.

Automated design of a uniform distribution using faceted reflectors

William J. CassarlyStuart R. DavidDavid G. JenkinsAndrew P. RiserOptical Research Associates3280 E. Foothill Blvd.Pasadena, California 91107E-mail: billc@opticalres.comThomas L. DavenportUniversity of ArizonaOptical Sciences Center1630 East University Blvd.Tucson, Arizona 85721Abstract. Faceted reflectors are a ubiquitous means for providing uni-form illumination in many commercial lighting products, examples beingnewer flashlights, department-store display lighting, and the faceted re-flectors found in overhead projectors. However, the design of facetedreflectors using software has often been more limited by the tools avail-able to design them than by the imagination of the designers. One of thekeys to enabling a broader range of design options has been to allowmore complex surfaces using constructive solid geometry (CSG). CSGuses Boolean operations on basic geometric primitives to define shapesto create individual facets. In this paper, we describe an improved fac-eted reflector design algorithm and use it to create a wide range of CSG-based reflectors. The performance of various reflectors is compared us-ing a Monte Carlo ray-trace method.

Method to improve spatial uniformity with lightpipes.

A heuristic method to obtain lightpipes that provide both collimation and good spatial uniformity is proposed. The change in shape that is likely to improve spatial uniformity, with minimal efficiency loss, can be predicted. Several case studies where this technique has been used are presented.

Target flux estimation by calculating intersections between neighboring conic reflector patches

We propose a fast algorithm to estimate the flux collected by conic reflector patches, based on the calculation of intersections between neighboring patches. The algorithm can be employed in conjunction with the supporting ellipsoids algorithm for freeform reflector design and is shown to be orders of magnitude faster and more scalable than the commonly used Monte Carlo ray tracing approach.

Illumination devices for photodynamic therapy of the oral cavity.

Three compact and efficient designs are proposed to deliver an average irradiance of 50 mW/cm2 with spatial uniformity well above 90% over a 25 mm2 target area for photodynamic therapy of the oral cavity. The main goal is to produce uniform illumination on the target while limiting irradiation of healthy tissue, thus overcoming the need of shielding the whole oral cavity and greatly simplifying the treatment protocol. The first design proposed consists of a cylindrical diffusing fiber placed in a tailored reflector derived from the edge-ray theorem with dimensions 5.5 × 7.2 × 10 mm3; the second device combines a fiber illuminator and a lightpipe with dimensions 6.8 × 6.8 × 50 mm3; the third design, inspired by the tailored reflector, is based on a cylindrical diffusing fiber and a cylinder reflector with dimensions 5 × 10 × 11 mm3. A prototype for the cylinder reflector was built that provided the required illumination for photodynamic therapy of the oral cavity, producing a spatial uniformity on the target above 94% and an average irradiance of 51 mW/cm2 for an input power of 70 mW.

Lightpipe device for delivery of uniform illumination for photodynamic therapy of the oral cavity

A compact and efficient lightpipe device to deliver light to the human oral cavity for photodynamic therapy was designed and fabricated, having dimensions 6.8 mm × 6.8 mm × 46 mm. An average irradiance of 76 mW/cm2 with an average deviation of 5% was measured on a square 25 mm2 treatment field for an input power of 100 mW. The device limits irradiation of healthy tissue and offers potential for improvement over the current treatment procedure, which requires shielding of the whole cavity to avoid damage to healthy tissue.

Freeform reflector design using integrable maps

We propose a design method for freeform reflectors based on source-target maps. The necessity for maps to fulfill the integrability condition to obtain a continuous reflector surface is discussed and demonstrated with various reflector geometries. We also review the advantages and drawbacks of reflectors with step discontinuities that do not require the integrability condition to be satisfied.