Nonimaging optics is the key technology for a range of applications that includes solar collection, lithography, fiber-optic illumination, display systems, and LED lighting. Some of the fundamental concepts and 'tricks of the trade' that are used when designing nonimaging optical systems are provided.

The air-gap RXI lens efficiently produces a very narrow beam from high-powered LEDs. This design has an aspect ratio of 5, with both front surface and reflecting back surface designed simultaneously from periphery inwards, as profiles of circular symmetry, via applying the edge-ray principle to the chip geometry. The light source is a Lambertian-glowing cube 1.2 mm square and 0.15 mm high, as viewed through its clear (n=1.54) package dome, with emission down to 95° from the symmetry axis. A given exit-aperture diameter defines a minimum, etendue-limited collimation angle, α=arcsin(chip-width/diameter). At the center of the back surface is a tailored quasi-hemispheric cavity surrounding the source and serving to uniformly distribute the source flux over the front surface. The front surface reflects that source flux to the back surface, which reflects it back forward again, accomplishing the optical folding thereby. The back surface is shaped so that the light it reflects forward will be refracted out the front surface to become the collimated output beam.

The Simultaneous Multiple Surface (SMS) method in 3D geometry is presented. Giving two orthotomic input ray bundles and other two orthotomic output ray bundles, the method provides an optical system with two free-form surfaces that deflects the rays of the input bundles into the rays of the corresponding output bundles and vice versa. In nonimaging applications, the method allows controlling the light emitted by an extended light source much better than single free-form surfaces designs, and also enables the optics contour to be shaped without efficiency losses. The method is expected to find also applications in imaging optics

Commercial adoption of non-imaging optics has been limited in part by high length-to-aperture ratios of classical designs. Previous low-aspect-ratio designs have been limited to particular angular ranges. We will present designs with length-to-aperture ratios of 0.6 or lower, with nearly ideal etendue-preserving performance and efficiency over a wide range of collection and output angles. The results described will include raytrace simulations, experimental results, and demonstration units.

Non imaging optics has established a reliable and sound framework for the design of efficient lighting systems in different application fields (nuclear physics, solar concentrators, electric lighting appliances,etc.). Based on its outstanding features, novel daylighting devices (anidolic daylighting systems)were designed in order to achieve efficient collection and redistribution of the diffuse component of daylight within deep office rooms. Several devices were set up, optimised through computer numerical simulations, built at different scales (1:10 scale models, 1:1 scale test modules)and finally monitored under different weather conditions (clear and overcast skies). An overview of the high luminous performance achieved by these daylighting devices --a zenithal anidolic collector, an anidolic ceiling and facade integrated anidolic systems --in 6 to 7 meters deep rooms under typical Central European weather conditions will be given in this communication. It will be shown that a very significant improvement of daylight factors monitored at a 5 meter distance from the facade is achieved by theses systems in comparison to a conventional double glazing reference facade (doubling of the daylight factors on the work plane), which corresponds to a substantial improvement of the daylight provision in the deeper part of the room.A daylighting system (anidolic slats) that shows the limits of building integration for such systems,will be considered as well.

Efficient hybrid luminaire development is an integral part of the Hybrid Solar Lighting Program at Oak Ridge National Laboratory. Hybrid luminaires are necessary to blend light from a fiber optic solar source with electric fluorescent lamps. The luminaire designs studied involve a commercially available fluorescent luminaire that has been modified to include optical elements for efficiently dispersing fiber optic solar light sources. Quantitative measurements of optical efficiency and spatial intensity distribution for two luminaire designs are compared.

Research is underway at Oak Ridge National Laboratory (ORNL) that could lead to entirely new, highly energy-efficient ways of lighting buildings using the power of sunlight. In addition to providing light, the hybrid lighting system will convert sunlight to electricity much more efficiently than conventional solar technologies using thermo-photovoltaic cells. In commercial buildings today, lighting consumes more electric energy than any other building end-use. It accounts for more than a third of all electricity consumed for commercial use in the United States. Typically, less than 25% of that energy actually produces light; the rest generates heat that increases the need for air-conditioning. ORNL is developing a system to reduce the energy required for lighting and the air-conditioning loads associated with it, while generating power for other uses. The system uses roof-mounted concentrators to collect and separate the visible and infrared portions of sunlight. The visible portion is distributed through large-diameter optical fibers to hybrid luminaires. (Hybrid luminaires are lighting fixtures that contain both electric lamps and fiber optics for direct sunlight distribution.) When sunlight is plentiful, the fiber optics in the luminaries, provide all or most of the light needed in an area. Unlike conventional electric lamps, they produce little heat. During times of little or no sunlight, sensor-controlled electric lamps will operate to maintain the desired illumination level. A second use of the hybrid lighting collector system is to provide sunlight for enhanced practical photosynthesis carbon dioxide mitigation. In this project the hybrid lighting collector system is being used to provide sunlight to a lab-scale photobioreactor for growing algae that is being used for CO2 mitigation. The end goal of this project is to provide a photobioreactor that can be used to mitigate CO2 in fossil fuel fire power plants. This paper will discuss the development and operating experience to date of two hybrid lighting solar collectors installed at ORNL and at Ohio University. The first hybrid lighting collector system was tested at ORNL and then installed at Ohio University in June of 2002. A second collector of the same design was installed at ORNL in September of 2002. The Ohio University collector system has been running continually since its installation while the ORNL unit has been operated in a research mode on most sunny days. They have operated with very little human interaction and this paper will summarize the development, operating experience, collection efficiency, as well as providing information on additional data being collected as part of the system operation.

We describe a practical method for precisely aligning the optical components of a low-cost solar concentrator developed for fiber optic solar lighting applications. A two-stage alignment process, involving both mechanical and optical alignment techniques, is described which allows the tilt, centering, and focal alignment of a large parabolic primary reflector relative to a segmented planar secondary mirror to be accurately determined. The alignment strategy is well suited to optical systems utilizing large reflectors with non-referenced optical axes and non-precision surface characteristics, as is typical of many inexpensive reflectors.

Luminous ceilings were developed in the 1940’s from a comprehensive mathematical study of the integral equations for the interflection of light in rooms. It was found that criteria for optimum vision are satisfied for most visual tasks and most shapes of rooms if the entire ceiling is the source of light and room reflectances are sufficiently high. In the 1950’s criteria for lamp spacing above the luminous panels were developed and many undecorated luminous ceilings were installed. To make the optimum luminous environment more attractive and interesting, hand-painted luminous ceilings were developed in the 1960’s and 1970’s and applied to homes, offices and classrooms. This paper presents the criteria for creating computer generated narrative luminous ceilings and gives practical examples applied to classroom lighting.

Due to their high relative cost, solar electric energy systems have yet to be exploited on a widespread basis. It is believed in the energy community that a technology similar to photovoltaic (PV), but offered at about $1/W would lead to widespread deployment at residential and commercial sites. This paper addresses the investigation and feasibility study of a low-cost solar thermal electricity generation technology, suitable for distributed deployment. Specifically, we discuss a system based on nonimaging solar concentrators, integrated with free-piston Stirling engine devices incorporating integrated electric generation. We target concentrator-collector operation at moderate temperatures, in the range of 125°C to 150°C. This temperature is consistent with use of optical concentrators with concentration ratios on the order of 1-2. These low ratio concentrators admit wide angles of radiation acceptance and are thus compatible with no diurnal tracking, and no or only a few seasonal adjustments. Thus, costs and reliability hazards associated with tracking hardware systems are avoided. Further, we note that in the intended application, there is no shortage of incident solar energy, but rather it is the capital cost of the solar-electric system that is most precious. Thus, we outline a strategy for exploiting solar resources in a cost constrained manner. The paper outlines design issues, and a specific design for an appropriately dimensioned free-piston Stirling engine. Only standard low-cost materials and manufacturing methods are required to realize such a machine.

New strategies for the efficient use of concentrated sunlight to synthesize carbon nanomaterials are described - approaches that offer a potentially far less expensive production facility that is also amenable to being scaled up, in contrast to the conventional costly technologies of laser ablation furnaces and plasma discharge chambers. Our designs employ solar fiber-optic mini-concentrators that completely decouple the collection and remote indoor delivery of solar radiation into a high-temperature nanomaterial reactor. High flux on the target graphite rod is produced by the overlap of low numerical aperture concentrator units - a strategy that also acommodates the sizable gap required between the target inside the reactor and the distal fiber tips on the reactor exterior. The reactor incorporates a nonimaging photon regenerator that traps thermal radiation emitted from the target. This in turn allows a dramatic reduction in solar input relative to earlier solar nanomaterial furnaces. Designs and performance estimates are provided for a systemwith target temperatures in excess of 3000 K, and hence with significant nanomaterial yields.

The Singapore Kranji racetrack complex includes a multi-tiered air-conditioned spectator facility with around 2000 m² of glazing that were plagued by excessive exterior condensation during nighttime events. The problem stemmed from a combination of high ambient humidity, warm outdoor temperatures and the required comfort cooling of the interior space. A number of mechanical and forced-convective heating solutions all failed to satisfy the severe constraints imposedon the placement of retrofit devices, e.g., not obscuring spectators' views, permitting a large view angle, ambient cross winds, and limited electrical capacity. We developed a compact efficient radiative solution based on nonimaging optics: highly asymmetric infrared reflectors, with the heating source being off-the-shelf rectangular ceramic elements. The challenges included: (1) achieving a high degree of flux uniformity on glazings 5 to 5.5 m in height and hundreds of meters wide; (2) luminaries having to be compact (about 20-40 cm in depth); and (3) luminaire siting being restricted to a small space close to, and just above, the glazing, out of the field of view of the spectators, which imposes a large and highly asymmetric field of irradiation. Good flux uniformity is essential for minimal electrical power requirements and the avoidance of hot spots that could prove annoying to spectators. Prototypes of our designs were fabricated, tested under worst-case conditions, and found to perform satisfactorily.

A novel solar power plant utilizes concentrator modules that track the sun by elevation-tracking modules on azimuth-tracking frames floating in shallow water. The entire floating circular platform is flat and only knee-high. The circles can be closely packed to cover 83% of the land, unlike the low percentages of conventional wind-loaded tracking mirrors. Each elevation-tracking module has multiple TIR lenses, each of which focuses sunlight onto one end of a glass rod that has the solar cell glued to its other end. These rods kaleidoscopically homogenize the focused hotspot uniformly over the square cell. The cells are cooled by conduction to the water, and operate only 10°C above the water temperature. The cell voltage is near that of the hydrolysis of water, enabling fuel cells to produce electricity at night.

Stable superpositions of elemental ray contributions give new capabilities for the ray-based analysis of optical fields and systems. These field estimates are constructed so that the results are effectively independent of the width of the field elements associated with each ray. The elements are thus free to be, more or less arbitrarily, localized or distributed at will. Since such elements thus need not disperse under diffraction, the new scheme is not a traditional beam summation method. In fact, it is this definitive property that leads to remarkable simplifications, and to significantly more accurate ray-based wave models. With this approach, error estimates become easily accessible, and a asymptotic treatment can finally be developed for fundamental processes such as refraction and diffraction.

A well-designed imaging zoom lens provides variable image magnification while maintaining good image quality. A zoom capability can also be of use in nonimaging optical designs. In this contribution we present a novel optimized design for a nonimaging projection system that provides high flux transfer efficiency over a wide range of angular beam widths, while maintaining good angular beam uniformity. A special feature of our design is that it is a doublet for which the two interior lens surfaces are precise negatives.

We consider the problem of designing illumination optics to optimally transfer light from an arc lamp to a rectangular LCD target. This problem is commonly solved in the video projector industry by employing a conventional elliptical reflector. In this contribution we investigate an improved hybrid optical concept comprising a compound elliptical reflect and an aspheric lens arranged in tandem. The design goal is to maximize the photometric flux incident on the rectangular entrance pupil of a light tunnel within a 30-degree acceptance angle relative to the optical axis. The light source is a 100W UHP arc lamp, characterized by means of photometric data measured by Radiant Imaging. A global optimization procedure was used to search for the set of optical-component shape and positioning parameters that provided maximum performance, while satisfying a set of design constraints. The resulting optimized hybrid design is compared to a baseline conventional elliptical reflector design and is shown to deliver 14% more light to the rectangular target.

Many non-imaging and imaging reflective illumination designs work great on paper, but are either very expensive to manufacture or significantly underperform their designers expectation. We report here on our first results of a new, high volume capable, low cost manufacturing processes that can be customized to build a wide range of high performance reflective illumination components (imaging and non-imaging) with all or most performance parameters simultaneously improved. This flexible manufacturing technology is based on the combination of high surface shape capable metal substrate manufacturing process with a compatible surface roughness improvement (SRI) coating. By example of an eele-enhanced lamp reflector module we will show that the manufacturing process improvements achieved for the projection display market are also capable of being adapted to manufacture higher performance, lower cost, reflective components for other illumination applications and wavelength ranges.

A solar collector/receiver for a full-spectrum solar energy system is being designed by a research team lead by Oak Ridge National Laboratory and the University of Nevada, Reno. This solar energy system is unique in that it utilizes the majority of the solar spectrum. The collector/receiver is a modified Cassegrain system that uses a large parabolic mirror and a secondary mirror comprised of multiple planar segments. The secondary mirror segments are coated with a spectrally selective cold mirror coating that lets the infrared (IR) energy pass through while reflecting the visible light. The focus of this paper is on determining whether a refractive or a reflective non-imaging (NI) tube will produce the most uniform irradiance of the IR energy on the thermophotovoltaic (TPV) array. It has been shown that a rectangular NI tube will work well for the prototype system3. The results herein show that a reflective NI tube will perform best for this system, with a short length, minimum/maximum flux ratio of 0.94 and power output of 37W. It is also shown that a square shaped TPV array can increase the optical efficiency by 9% and the overall system efficiency by 2%.