Size- and structure-dependent efficiency enhancement methods are studied for luminescent solar concentrators (LSCs) fabricated by casting organic laser dyes into PMMA matrixes. The enhancement are achieved mainly by attaching a white diffuser with an airgap at the bottom of the LSC and adding refractive index matched optical gel between the LSC's edges and the attached photovoltaic cells. The size-dependent efficiency enhancement is studied for a single layer by changing the size up to 120 cm. The results show that the enhancement from the white diffuser drops and then tends to plateau at a certain size of LSC. This also applies to multilayer LSCs. Together with optical gel, the efficiency enhancement is higher for multilayer structures than that for single layers. We also demonstrate the optimal length for the design of LSCs due to reabsorption of dyes. These results could be applied to optimize the design of other LSCs.
A luminescent solar concentrator (LSC) generally is a sheet of highly transparent materials embedded with luminescent
materials. Incident sunlight is absorbed by the luminescent materials, and then emitted through down conversion process
at longer wavelengths. A large portion of the emitted light is trapped in the sheet and travels to the edges where
photovoltaic solar cells are attached. In this study, we investigate the optical enhancement methods for LSCs with
different sizes mainly by using optical gel and white diffuser. The largest tested LSC is up to 1.2m in length and with
geometrical gain 64. This is, as we know, the largest reported size. It yields electrical gain 3.9 by optical enhancements.
And the optical efficiency is still as large as 10%. The study shows that the enhancement by white diffuser is more
sensitive to the size of the LSCs than that of the optical gel. Such enhancement drops with the increase of the sizes of
LSC, but tends to plateau at certain size.
Quantum dot (QD) luminescent solar concentrator (LSC) uses a sheet of highly transparent materials doped with
luminescent QDs materials. Sunlight is absorbed by these quantum dots and emitted through down conversion process.
The emitted light is trapped in the sheet and travels to the edges where it can be collected by photovoltaic solar cells. In
this study, we investigate the performance of LSCs fabricated with near infrared QDs (lead sulfide) and compared with
the performance of LSCs containing normal visible QDs (CdSe/ZnS), and LSCs containing organic dye (Rhodamine B).
Effects of materials concentrations (related to re-absorption) on the power conversion efficiency are also analyzed. The
results show that near infrared QDs LSCs can generate nearly twice as much as the output current from normal QDs and
organic dye LSCs. This is due to their broad absorption spectra. If stability of QDs is further improved, the near infrared
QDs will dramatically improve the efficiency of LSCs for solar energy conversion with lower cost per Wp.
In the design of illumination lenses, there is a fundamental incompatibility between the spherical geometry of light radiating outwards and the rectangular geometry of typical illumination targets, analogous to trying to fit a round peg in a square hole. This amounts to establishing a rectangular grid on the sphere, the perennial problem of map-makers. Here we apply a new pseudo-rectangular spherical grid, originally developed for parallel-processor simulations of semiconductor devices, to establish correspondence between source-grid cells and the rectangular cells of a target grid. This correspondence establishes a grid of deflections, whereby source rays are deflected so as to impact the proper cell on the target grid. For a given lens refractive index, each deflection is implemented by the angles of inclination the ray encounters going into and out of the lens, resulting in two grids of surface gradient values, for the inside and outside lens-surfaces. Central spines are obtained for these surfaces by a linear integration, after which adjacent rows are successively obtained in a lawnmower fashion, so as to heal any imcompatible cross-derivatives. Example lenses are illustrated.
The ubiquitous downlight inhabits our ceilings by the millions. Hot, inefficient, and electrically wasteful, it is next in line for replacement by the latest high-brightness, high-efficacy white LEDs. The conventional downlight configuration of a large incandescent spotlight in a low-cost, ceiling-recessed metal can, represents the culmination of old technology, fated never to improve significantly. Incandescent downlights add greatly both to direct and indirect electrical consumption, with the lamps requiring relatively frequent replacement. The small size of LED emitters means small optical elements can produce much higher-quality beams than incandescent spotlight-lamps can produce. Herein we introduce compact high-luminosity LED downlights with lenses that deliver uniform illumination to delimited targets such as tables. One version utilizes circular lenses and micro-diffuser films to deliver square outputs. The other uses lenses cut to the target shape. In particular, one of these lenses is the first to offer a semicircular spot suitable for gambling tables.
LED tapes are emerging as cost effective light sources for longitudinal applications, such as strip lighting and accent lighting on buildings, and shelf and cove lighting for interior lighting. Such applications can be sorted into direct viewing and illuminative. In the latter, uniform illumination is the most frequent desideratum, particularly on nearby surfaces spanning large solid angles from the light source. The LED tape by itself creates a hot line directly underneath it and relatively dim illumination at target's distant edge. Instead, extruded refractive lenses have been prototyped that spread out the light such as to provide uniform illumination over nearby target zones. Different lens profiles are available for different lighting configurations, via the redistribution of the light field of the LED tape. Each lens acts as a magnifier where candlepower is required for distant slanted surfaces and as a de-magnifier towards the closest surfaces.
The design of illumination lenses is far easier under the regime of the small-source approximation, whereby central rays are taken as representative of the entire source. This implies that the lens is much larger than the source's active emitter, and its entire interior surface is nowhere close to the source. Also, a given source luminance requires a minimum lens area to achieve the candlepower necessary for target illumination. We introduce two-surface aspheric lenses for specific illuminations tasks involving ceiling-mounted downlights, lenses that achieve uniform illuminance at the output aperture as well as at the target. This means that squared-off lenses will produce square spots. In particular, a semicircular lens and a vertical mirror will produce a semicircular spot suitable for gambling tables.
Conventional linear light sources irradiate cylindrically, into 360° in a circle orthogonal to the lamp axis. This makes it difficult to optically couple lamp-output to a much narrower range of output directions. Light-emitting diodes, however, emit into a hemisphere or less of solid angle, and thus are much more amenable to proper lensing. Recent LED tape systems have ±60° emission angles, due to recessing the emitting chips in reflector cups. This turns out to be highly beneficial to linear lenses, enabling nearly 100% collection efficiency. Here we present a new class of nonimaging linear lenses with two aspheric profiles, designed according to the amounts of source-light received along longitudinal strips on the interior surface of the linear lens. In the small-source approximation, the light falling on each strip is imaged relatively intact in the far field, although the source itself is not. This enables the design of extruded linear lenses achieving uniform illumination of nearby planar targets, as in shelf and cove lighting.
This paper begins by reviewing the current state of development of LEDs, their existing markets as well as their potential for energy conservation and their potential for gaining market share in the general illumination market. It discusses LED metrics such as chip size, lumens per watt, thermal resistance, and the recommended maximum current rating. The paper then goes on to consider the importance of non-imaging optics for both optically efficient and extremely compact LED lighting systems. Finally, microstructures useful for controlling the fields-of-view of LED lighting systems are considered and described in some detail. An extremely efficient and cost effective microstructure, called kinoform diffusers, is shown to have very unique properties that make this technology almost ideal for shaping the output beams of LED lighting systems. It concludes by illustrating some general illumination LED lighting systems
We present an efficient and effective collimating lens system for LEDs. It consists of two lenses: an immersive ball lens within which an LED die is optically bonded, and an adjacent collimating lens that produces uniform illumination at its output plane. The three surfaces of the system are numerically tailored in accordance with the angular distribution of light emitted by the die. When the immersion lens is surface-tailored, the resultant shapes are sufficiently close to a spherical surface that the manufacturing convenience and low cost of an exact sphere make it the preferred shape. The immersion ball-lens reduces the angular spread of the LED's light from +/- 90 degrees to +/- 60 degrees in air. The bottom surface of the collimating lens redirects each light ray to its proper place (axial radius) in the output beam, at which point the top surface redirects the ray to become parallel to the optical axis. Uniformity of output illuminance occurs when a ray's proper place is determined by its place in the cumulative angular distribution near the immersed source. Three surfaces suffice to give highly efficient collimation as well as spatial uniformity of the output beam.
Powerful new LEDs provide enough luminosity for a single one to illuminate a transparent EXIT sign, but efficient injection means are required, with luminance-uniformity a prime goal. We present a totally-internally-reflecting `Black Hole' indentation on the waveguide surface. This cuspated configuration deflects the light from an immersed LED, aimed perpendicular to the plane of the waveguide, into guided light trapped within the slab, to be extracted by the sign's alphabetic features. In spherical coordinates, a +/- 60 degree(s) output cone (for example) is deflected into the 360 degree(s)-azimuth guided range of +/- 47 degree(s). That is, this reflector transforms a polar cone into an equatorial swath, a symmetry that is useful whenever the total horizon must be dealt with, just as a lighthouse, or better yet a marker buoy, must send warning light to all the quarters of the compass. In its circularly symmetric configurations, this device offers a removable disc, optically bonded to the LED source, that completely hides the source from view above the indentation. Non-waveguide, stand-alone illumination applications include aircraft-warning beacons, alarm flashers, and near-field illuminators.
The Total Internally Reflecting (TIR) lens is a faceted structure composed of prismatic elements that collect a source's light over a much larger angular range than a conventional Fresnel lens. It has been successfully applied to the efficient collimation of light from incandescent and fluorescent lamps, and from light-emitting diodes (LEDs). A novel LED-powered collimating backlight is presented here, for uniformly illuminating 0.25'-diagonal miniature liquid- crystal displays, which are a burgeoning market for pagers, cellular phones, digital cameras, camcorders, and virtual- reality displays. The backlight lens consists of a central dual-asphere refracting section and an outer TIR section, properly curved with a curved exit face.
We present a novel condenser system based on a nonimaging TIR lens and an associated apodizing aspheric lens. This system provides uniform collimated illumination of the image plane of a projector such as an overhead viewgraph or LCD projector. The TIR lens enables the system to be very compact. The aspheric lens lies between the light source and the TIR lens, so that the TIR lens output illumination is spatially uniform.
We present two new applications for light emitting diodes of the Total Internal Reflection (TIR) lens, a non-imaging optical device presented at previous SPIE conferences on nonimaging optics. The first is a flat circularly symmetric lens that efficiently forms a highly collimated beam from the light output of Hewlett-Packard's Super Flux LEDs. The second is a linear TIR lens with die-on-board LEDs of several wavelengths positioned along its focal line. HP's Super-Flux LED package has an output half angle of 55 degree(s). Only the TIR lens can accept such a wide range for beamforming, and do it with high efficiency. We have designed and prototyped 1' models with half-power half angles of only 1.5 degree(s), utilizing a hyperbolic central section in place of the usual Fresnel lens. There are numerous applications for arrays of these lenses, since they emit more lumens per electrical watt than filtered incandescent lamps with parabolic mirrors. Moreover, they are more compact than conventional lamps, and LED lifetimes are much longer. The TIR lens in its linear form has been applied successfully to fluorescent downlighting products with much narrower transverse illumination angles than previously available with trough mirrors. More recently, light emitting diodes (LEDs) have been placed on the focal line of a linear lens. In this paper, we describe the optical properties and biomedical applications of the linear TIR lens when the LEDs have several different emission wavelengths. This single device can uniformly illuminate an extended target with several wavelengths either simultaneously, sequentially, or in complex programmed combinations. It can replace the complex systems of dichroic mirrors used with conventional white-light sources.
The total internal reflection lens has been successfully applied to the efficient collimation of light from incandescent lamps and light-emitting diodes, and it is currently being marketed in several retail products. These circularly symmetric designs operated with relatively small sources. Two new forms of the TIR lens have been designed, and prototypes fabricated, for forming beams from fluorescent lamps. The toroidal fluorescent lamp is formed by circularly sweeping a faceted profile about its outer edge. A 5 inch diameter prototype lens has been diamond turned, and has 80% efficiency. When covering a 2.5 inch toroidal source of 0.25 inch minor diameter, it forms a smooth structureless beam of 40 degrees FWHM. The linear TIR lens has a faceted profile that is extended in cylindrical symmetry. In conjunction with a planar back mirror, a 6 inch diameter lens collects 85% of the light from a 5/8 inch lamp. The full width at half maximum is 30 degrees transversely and 120 degrees longitudinally, in a stripe pattern with twin peaks at +/- 47 degrees parallel to the lamp axis. These designs are applicable to other tubular light sources: discharge lamps, such as aircraft strobes and camera flashlamps, as well as neon lamps. They offer greater efficiency, narrower beamwidths, and much more compact profiles than conventional relfector designs.
an electrooptic polymer with chlorophenol red dye and type-A photolime gel was demonstrated. The electrooptic coefficient (gamma) <SUB>33</SUB> in the direction of the poling field was measured to be 28 pm/V. Chlorophenol red in polymer showed a 1/e relaxation time constant of 820 hours, which is more stable than other dye demonstrated previously to be electrooptic in the same polymer.
The total internal reflection lens is a multi-faceted non-imaging device that was introduced in a paper we presented at the SPIE Non-Imaging Optics conference two years ago, with emphasis on solar-energy concentration. This paper will discuss the concentration on a target of the light emitted omnidirectionally from a compact source, such as an incandescent filament, a light- emitting diode, or an arc lamp. The converging type of TIR lens can efficiently concentrate this light into the relatively restricted range of acceptance angles typical of optical fibers and image illumination subsystems. It can replace the conventional ellipsoidal reflector and is superior to it in two ways: (1) its interception efficiency is considerably higher, when used with a back mirror; (2) its aberrations are lower in magnitude, because of the additional degrees of design freedom possible in the three-faced facets of the TIR lens. However, it is more sensitive to lens optical quality, so that theoretically possible results are best achieved with diamond-turning of lenses or molds. Also, TIR lenses are sensitive to errors in source position.
A compact non-imaging lens is described and analyzed: the Totally Internally Reflecting (TIR) lens. It constitutes a major class of optical devices distinct from reflectors and Fresnel lenses. It is a transmissive device that redirects light passing through it via the action of a multiplicity of prismatic facets basically acting as annular Harting-Dove prisms that rotationally `wash-out' image structure. They can achieve much larger bend angles (well over 90 degree(s)) than those of the refraction-only facets of Fresnel lenses. As a consequence, TIR lenses are extremely compact, typically having a thickness about one fifth their diameter. This paper discusses their applications as collimators for small light sources (LEDs and HID lamps), injectors for fiber- optic illumination systems, and solar concentrators, and how close their performance comes to the ideal thermodynamic limit.
TLR holograms have been used to generate 0. 5 jim resolution images with illumination by an Argon laser operating at 457 nm. The contact (proximity) printing geometry compatible with standard wafer processing was used for the recording and reconstruction processes. In order to eliminate the expensive and bulky construction involving a prism a backside holographic wave coupler is proposed. 1.