Illumination engineering is a nascent field in the broader category of optical engineering. The what, where, when, and who leads us to why illumination engineering is now a field in demand. This introductory talk to this year's Nonimaging Optics and Efficient Illumination Systems IV conference touches briefly upon the former queries. It ends with a discussion of the monetary dynamics, especially commercial products, electricity costs, and forecasts for the future.

High efficiency distributed lighting systems for general lighting applications, delivering light comparable to but with an energy saving of 80% or more over traditional sources have recently become available. This remarkable achievement is due to: the development of long lived high efficiency light sources that match the color rendition and warmth of traditional incandescent and fluorescent sources; the creation of a new generation of non-imaging collectors to efficiently collect and direct the light; and the availability of low loss and low cost light pipes to distribute the light. Given these improvements many incandescent, halogen and even fluorescent applications are now best served using fiber optic lighting technology. In achieving practical systems, a number of significant technical problems have been overcome. In this paper we shall review some of these solutions as well as indicate our view of the direction and impact of future advances.

Electric lighting is responsible for a significant fraction of electricity consumption within non-residential buildings. Making daylight more available in office and commercial buildings can lead as a consequence to important electricity savings, as well as to the improvement of occupants' visual performance and wellbeing. Over the last decades, daylighting technologies have been developed for that purpose, some of them having proven to be highly efficient such as anidolic daylighting systems. Based on non-imaging optics these optical devices were designed to achieve an efficient collection and redistribution of daylight within deep office rooms. However in order to benefit from the substantial daylight provision obtained through these systems and convert it into effective electricity savings, novel electric lighting strategies are required. An optimal integration of high efficacy light sources and efficient luminaries based on non-imaging optics with anidolic daylighting systems can lead to such novel strategies. Starting from the experience gained through the development of an Anidolic Integrated Ceiling (AIC), this paper presents an optimal integrated daylighting and electric lighting system. Computer simulations based on ray-tracing techniques were used to achieve the integration of 36W fluorescent tubes and non-imaging reflectors with an advanced daylighting system. Lighting power densities lower than 4 W/m² can be achieved in this way within the corresponding office room. On-site monitoring of an integrated daylighting and electric lighting system carried out on a solar experimental building confirmed the energy and visual performance of such a system: it showed that low lighting power densities can be achieved by combining an anidolic daylighting system with very efficient electric light sources and luminaries.

The performance of the XR solar concentrator, using a high efficiency multi-junction solar cell developed recently by Spectrolab, is presented. The XR concentrator is an ultra-compact Nonimaging optical design composed of a primary mirror and a secondary lens, which can perform close to the thermodynamic limit of concentration (maximum acceptance angle for a given geometrical concentration). The expected acceptance angle of the concentrator is about ±2 deg for a geometrical concentration of 800x (a Fresnel lens and secondary system typically has ±0.6 deg of acceptance for 300x of geometrical concentration). This concentrator is optimized to improve the irradiance distribution on the solar cell keeping it under the maximum values the cell can accept. The XR concentrator has high manufacturing tolerance to errors and can be produced using low cost manufacturing techniques. The XR is designed with the Simultaneous Multiple Surface (SMS) design method of Nonimaging Optics. Its application to high-concentration photovoltaics is now being developed in a consortium led by The Boeing Company, which has recently been awarded a project by the US DOE in the framework of the Solar America Initiative.

A new two mirror concentrating photovoltaic system making use of Kohler integration is introduced. Brief design background is included to show on paper operation principles. Test results from the first units are given and a full sixty mirror system is under construction.

Light scattering materials have several uses in solar energy applications, ranging from a purely aesthetic function as a cover glass to a way of increasing the path-length of photons inside a semiconductor. Knowing the transmittance of such elements is of essence to properly model, simulate, and design a solar energy system. The traditional method for obtaining the transmittance is to use a spectrophotometer fitted with an integrating sphere detector. However, it is well-known that most commercial integrating spheres underestimate the true transmittance of thick scattering samples. This study investigates a method to obtain quantitative values of the losses associated with measuring a scattering sample. The International Commission on Glass (ICG TC-10) is conducting an inter-laboratory comparison (ILC) on scattering samples to improve the methodology for characterizing such samples. A fritted glass sample similar to one in the ILC was used as an example. One side of a clear glass sample has a highly scattering layer. The bi-directional transmittance distribution function (BTDF) for the sample was obtained using a goniophotometer and then used as scattering function in a ray-tracing simulation. The ray-tracer was configured to report the amount of light exiting all six surfaces of the sample as well as through various ports defined by the integrating sphere geometry. The sample was then measured with a commercial integrating sphere in several different configurations, verifying the accuracy of the model.

Elliptical reflectors are widely used to couple the radiation of a light source into an optical system. Such a system usually collects the light with an integrating rod, a fiber, or any other kind of light guide. Its entrance window can be conceived as an aperture and an acceptance angle. In illumination designs with elliptical reflectors, sources and apertures are usually positioned in the focal points of the ellipse, probably due to the fact that the foci form a stigmatic pair. This is then implicitly generalized to the case of extended sources and apertures. Surprisingly, a careful investigation revealed that the maximum coupling efficiency is achieved if source and target are not positioned in the focal points. In this paper, a theoretical explanation of this effect is given by a calculation of higher-order magnification properties of an elliptical reflector. Finally, applications in current reflector designs for video projection lamps are shown.

The optimization of mirrors with respect to efficiency is a common task of illumination engineering. To solve this optimization task various numerical methods and methods that make use of partial or ordinary differential equations are described in the technical literature. Applying these methods one is often faced with the problem of finding a good starting configuration that can then be refined. A method has been developed that allows to determine a good starting configuration in a systematic way. The analytical approach can be used as a guideline through "parameter space" and gives inside into the parameter dependencies. It has first been applied to special geometries. In this contribution, it will be shown how the method can be generalized and applied to mirrors that feature different geometries. To this end, the analytical description will be put on a slightly broader basis. Special emphasis will be laid on showing how to describe optical reflectors with a relatively low symmetry, because they are frequently encountered in engineering practice. The analytical method leads to an integral expression that features the parameter dependencies. In a way, this approach might be considered analogous to describing an imaging optical system in the paraxial approximation to understand its key feature before starting aspherization of the optical surfaces.

In a previous paper we derived a generalized functional method of nonimaging optical design, applicable in the case of axisymmetric or translationally symmetric geometries utilizing extended sources and multiple reflective and/or refractive optical surfaces. Variations of this method were described for generation of either a prescribed intensity distribution as a function of angle or a prescribed irradiance distribution as a function of position along the shape profile of an aspheric target surface. A dual-surface functional (DSF) method was described for generation of two successive optical surfaces that transform a given source distribution into either two prescribed irradiance distributions on successive target surfaces or a prescribed irradiance distribution and a prescribed intensity distribution. The RMS difference between the intensity or irradiance distribution produced by a given generalized-functional design and the corresponding prescribed distribution approaches zero in the limit as the optical characteristics of the actual source approach those of the zero-étendue extended source model used in generating the design. In the current contribution, we present an iterative algorithm that can significantly improve the beam-shaping performance of generalized functional designs for sources having non-zero étendue. Three examples are provided, including an iterative DSF design that provides both high irradiance uniformity and étendue-matched flux-transfer efficiency greater than 97%.

Asymmetric reflector aberrations worsen illuminance uniformity and distort illuminance pattern. Using trough reflector design as an example, the aberrations are found significant in the design where the β angle coverage is in low number zones. In that situation an alternative approach could be used to achieve the same if not better illuminance uniformity. Besides target position, optical planning is also found a factor influencing the actual illuminance distribution although its impact is limited. An intensity-based reflector design method with both normalizing factor and reflector reflectance incorporated as variables is applied to compare all the designs. A new calculation method using α angle to acquire (x, y) coordinates is used to generate the reflector profiles.

An etendue efficient, prism-based LED color mixing scheme is presented in this paper. The prisms have dichroic coatings deposited on their diagonal surfaces and serve as beam splitters which selectively pass or reflect light of different wavelengths. Light confinement within the prisms is achieved through waveguiding, which is first explained in theory, and then verified by some preliminary experimental results. The compact size of this device makes it especially attractive for miniaturized projector systems.

Colored variable lighting is being used in more and more locations to enhance the "beauty" and "atmosphere" of interiors and exteriors. Lamps based on different colored LED are an obvious choice for such systems. The light from the differently colored LEDS needs to be mixed together very well because otherwise objects in the beam could create colored shadows. The difficulty is that we often want a lighting system where the light is collimated, where we can set the color of the beam, and where the lamp is as small as possible with an as small as possible exit diameter. This means that ideally we would like to mix colors etendue preserving. In this paper we discuss a new method of color mixing with dichroic color filters, which aims to achieve this. It is based on a special arrangement of the color filters, whereby the filters act as collimators. We have build prototypes and have done raytracing simulations. These show that we can indeed mix light of different wavelengths and make relatively small, color-variable, collimated, high brightness, light-sources. The advantages are an increase in brightness, a reduction/elimination of the colored shadows, and a small volume. This new method can, e.g., be used in spotlights, mini-beamers and logo projectors.

The brightness of many lamps, and hence the attainable power density at the target application, can be enhanced by recycling light back into the lamp's radiant zone. We report measurements of the effectiveness, spectral characteristics and modified plasma brightness maps that result from light recycling with a specular hemispherical mirror in commercial 150 W ultra-bright Xenon short-arc discharge lamps. Lamp brightness can be increased by up to 70% for certain spectral windows and plasma arc regions. However, lamp geometry reduces overall light recycling effectiveness to about half this value. This study was motivated by biomedical and high-flux furnace applications where the full spectrum of lamp emissions can be exploited, heightened brightness allows a broader range of procedures, and the design of the affiliated optical systems is contingent upon how plasma radiometric characteristics are altered by photon regeneration.

The latest generations of ultra-bright Xenon short-arc discharge lamps have prodigious emissions outside the visible spectrum, primarily in the near infrared. Their brightness distributions are spatially and angularly inhomogeneous due to both the pronounced non-uniformities of the plasma arc and the substantial infrared radiation from the hot electrodes. These characteristics are fortuitously favorable for applications in photonic surgery, biomedical diagnostics, high-temperature chemical reactors and furnaces: cases where the full lamp spectrum is utilizable, and the key is reconstituting the spectral power density of the optimal regions of the lamp's plasma at a remote target. The associated optical systems must be tailored to lamp radiometric properties that are not extensively available and invariably are restricted to visible light due to their widespread use in projection systems. We present experimental measurements for the spectral, spatial and angular distributions of 150 W lamps of this genre, and relate to their ramifications for broadband high-flux applications.

Since its beginnings, light-emitting diode (LED) has progressed toward greater performance. Today, LEDs are everywhere, in many shapes, and with a wide range of radiation patterns. We propose a general analytic representation for the angular intensity distribution of the light emitted from an LED. The radiation pattern equation is determined by adding a Gaussian or a power cosine expression for contributions from the emitting surfaces (chip, chip arrays, or for some cases a phosphor surface), and the light redirected by the reflecting cup and the encapsulating lens. Mathematically, the pattern is described as a sum of Gaussian or of cosine-power functions. The resulting equation is widely applicable for any kind of LED of practical interest. We successfully model the radiation patterns from several manufacturer datasheets.

In the last years it has been shown that efficient collimator systems for point sources can be designed with the flux tube method in combination with an optimiser. In this paper it will be shown that this method can be extended to extended light sources. Various collimator designs for different types of sources will be discussed that transform the illuminance into imposed distribution.

The application of NURBS or Non-Uniform B-Splines in free-form optical design has existed for several years. There are cases however where NURBS geometry presents limitations. Tuning the control points of a spline patch may require a large number of faceted polygons to obtain fine structure. The knot pairs in either a uniform or non-uniform B-spline surface require rectangular grid arrangement. Although knot insertion retains surface continuity it adds superfluous complexity as knots require the insertion of entire rows of control points. Adding rows of control points for each new knot to satisfy the NURBS topology needlessly complicates the optical control surface. Stitching together NURBS patches also produces a high probability of continuity error at rib patch junctions which can produce unwanted ripples and holes. The computational cost for altering seed patch control points at NURBS spline patch junctions hampers the performance of a global non-imaging optimizer and reduces the possibility of exploring the more interesting areas of a problem topology within realistic time constraints. Advancements in CAGD or Computer Aided Graphic Design which overcome the common limitations of NURBS can significantly improve free-form possibilities. In most cases control points can be reduced by 60% or more to represent the same free-form geometry. T-splines and other recent CAGD advancements also accelerate local refinement by simplifying control point addition, allowing the designer to increase optical control surface detail where needed.

Illumination design continues to advance through the increased use of computer simulations and advances in design and optimization tools. One of the key elements for robust illumination optimization is the creation of merit functions which allow optimization algorithms to compare whether changes in the illumination system improve the performance. A robust illumination merit function is described and its use is illustrated with a number of examples.

The application of ultra bright monochromatic and white High-Power-LEDs in the range of automotive lighting systems is now state of the art. These LEDs offer new possibilities in optical design and engineering within different fields of automotive lighting, e.g., tail lamps, signal lamps, headlamps and interior lighting. This contribution describes the process of the optical design of an automotive LED tail lamp based on a practical example. We will elaborate the principal geometric approach, the radiometric conditions and the optical design by using standard and advanced mathematical optimization methods. Special attention will be paid to the following topics: efficient light coupling from the LED into the optical device, adaptation of the illuminance and optimization with respect to the requirements from SAE/ECE regulations. It will be shown that the development of LED-lamps requires the complex interaction of several factors. The challenge for the optical designer is to fulfill the technical demands while also considering the appearance of the final product desired by the customer. Further design specifications emerge from the electrical and thermal layout of the lamp.

Although white LED lumen output and luminance have both substantially been increased in the last few years, multiple LEDs are still needed, at present time, to meet automotive forward lighting such as low beam headlamp photometric specifications. Use of multiple LEDs in combination with optics is often constrained by the lamp size. With the goal of minimizing the number of LEDs used in an automotive forward lighting design, further studies have been conducted to optimize reflector optics for the fog lamp and headlamp low beam applications. The studies included different types of LEDs by means of lumen output and effective emitting area. In addition, the system étendue and its optical transformations have been taken into considerations in the studies.

For switching viewing angles of a liquid crystal display, we proposed to place a liquid crystal device between an LED and a light-guide of a backlight. The first key component for this configuration is a light source with electronically-controlled emission angles. Here, we construct such a device by stacking an optical film and a polymer-network liquid crystal (PNLC) cell on top of a chip-type LED. The optical film contains opaque parallel plates that limit the LED output in a narrow angular range. The PNLC cell either transmits or scatters the light emerging from the optical film. Experiment using a 15μm-thick PNLC cell shows that the angular distribution becomes 2.3 times wider by turning off the PNLC cell. We place this light source at one end of a light-guide so that the angular distribution of the light propagating inside is controlled. The second key component is some types of micro-strucrures built on the light-guide to out-couple the propagating light. We first attached various optical films on a light-guide surface. Although the angular distribution of the extracted light was switched successfully, light was mostly emitted into an oblique direction, approximately 60° from the plane normal. Next, we used a half-cylinder in place of the optical films. The curved surface of the cylinder was attached to the light-guide with a small amount of matching oil, which constituted an optical window. We measured that the angular distribution of the extracted light decreased to 35° FWHM from 62° FWHM by turning on the PNLC cell.

The design, manufacture and testing of lightweight Carbon Fiber Reinforced Polymer (CFRP) converging spherical mirrors for the RICH-1 Cherenkov detector of LHCb are described. The mirrors have low areal density to minimize the amount of material in the path of traversing particles and need to be fluorocarbon compatible to avoid degradation in the C₄F₁₀ radiator gas. The total area is about 2m² and high reflectivity (typically 90%) over the wavelength range 200-600nm is required.

Compact expressions are presented to represent the geometric shape of a reflector in terms of the optical path length to a receiving surface. These expressions are used to calculate the mapping between input rays and output rays, and differentiation of these expressions allows calculation of the illumination on the receiving surface. The scalar value of an optical path length, evaluated on an illuminated surface, is used as a basis to construct a potential function in three-space. The value and gradient of this potential function are used to define a system of rays, and to solve for the mapping between input rays and output rays. A result due to Oliker, concerning the existence of solutions to a near field illumination problem, is discussed. This existence result is used in a continuity argument regarding the nature of the mapping between input ray directions and incident points on a receiving plane. It is argued that the mapping from input ray directions to incident points on a receiving plane is common to a family of reflectors that produce the same illuminance distribution. Another mapping, describing the flow of illumination as a reflector is deformed, is also discussed. A fluid mechanics analogy is explored, and a new method for reflector design is proposed.

A novel light-emitting diode backlight module applied in liquid crystal displays is demonstrated. With microgrooves on the bottom surface and diffusive dots on the upper surface of the light guide plate (LGP), most of the incident backlight is utilized effectively and the dispersion of light is decreased obviously. The design procedure of optimization for the backlight module is accomplished by the TracePro optical simulation software. Relationship between the dimensions of microgrooves and diffusive dots are investigated and discussed in detail. By using the structure of microgrooves and diffusive dots on the LGP, the incident light satisfies the total internal reflection conditions and reflects from the bottom surface then spread by the diffusive dots. Compared to the conventional backlight devices, the light uniformity and light intensity for the LGP are improved by our design.

This paper presents a molecular dynamics (MD) scheme for the automatic generation of dot patterns for the light guides used in LCD backlight modules. Several MD computational techniques are integrated with the conventional MD scheme to enable the adjustment of the dot density in specific regions of the light guide in order to create a dot distribution with a high dot density variation and a high spatial uniformity. These techniques include the cell division technique, the variable r-cut technique, the boundary smoothing technique and the reflective boundary condition. The reflective boundary condition enables a precise control of the dot density within each cell, and is instrumental in achieving a dot distribution with both a high dot density variation and a high spatial uniformity. The performance of the proposed dot generation scheme is verified by considering the practical example of the dot pattern design of a light guide with a single LED light source located in the lower-right corner. The numerical results confirm the ability of the proposed method to achieve an even luminance condition by establishing a dot pattern whose density increases concentrically with an increasing distance from the light source.

At application of "pillow optics" for signal automotive lights some natural contradiction can occur between official requirement for angular distribution of Intensity (the beam should have rectangular form) and real light Intensity pattern radiated, which usually has circular or oval shape. This oval area should be bigger, than needed a rectangular pattern. Significant portion of the light misses target area; and this light is lost in such cases. Some other shape of surface is proposed for pillow optics to improve light pattern.