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More than ever, society needs research breakthroughs to address major problems. Universities have a key role to play in discovering the required new knowledge and guiding its application. However, since World War II, universities have been encouraged to focus mainly on curiosity-based research, with corporations carrying out practical work. This division worked well in the last half of the 20th century, when there was considerable funding for long-term research in the laboratories of major corporations. Today, however, those firms face greater competition, and the resultant financial constraints have foreshortened their research time-horizons. Universities are poised to compensate by re-emphasizing long-term, application-oriented research, but great care must be taken to strengthen fundamental research as well. These objectives can be achieved simultaneously by bolstering a time-honored class of research projects labelled Highly Integrative Basic And Responsive (HIBAR), each of which combines fundamental and applied approaches through partnerships with practical experts. This approach will help repli- cate, within universities, the breakthrough-generation capacity that once flourished in major corporate laboratories. Toward this end, a network of universities called the HIBAR Research Alliance (HRA) has recently formed to strengthen HIBAR research, both by helping universities to encourage it (while also improving equity, diversity, inclusion, and academic freedom) and by helping researchers to carry out HIBAR research projects (while also advancing their careers). The HRA aims to increase the rate of HIBAR research projects in universities—from about one project in 20 today to one in five by 2030—while strengthening all types of research excellence.

Color-normal subjects sometimes disagree about metameric matches involving highly structured SPDs, because their cone fundamentals differ slightly, but non-negligibly. This has significant implications for the design of light sources and displays, so it should be estimated. We propose a broadly applicable estimation method based on a simple adaptive "front-end" interface that can be used with any selected standard color appearance model. The interface accepts, as input, any set of color matching functions for the individual subject (for example, these could be that person's cone response functions) and also the associated tristimulus values for the test stimulus and also for the reference stimulus (i.e. reference white). The interface converts this data into tristimulus values of the form used by the selected color appearance model (which could, for example, be X, Y, Z), while also carrying out the needed transform, which is based on an estimate of the subject's likely previous long-term adaptations to their unique cone fundamentals. The selected standard color appearance model then provides color appearance data that is an estimate of the color appearance of the test stimulus, for that individual subject. This information has the advantage of being interpretable within that model's well-known color space. The adaptive front end is based on the fact that, for any selected input SPD and the subject's unique color matching functions, there can be many different SPDs that are metameric for that individual. Since observer-to-observer color perception differences are minimized for spectrally smooth SPDs, smooth metamers predict color appearances reasonably accurately.

LED lighting provides considerable flexibility for shaping the light spectrum for different applications, including increasing the color gamut. While the spectra are typically designed for their effects on observers with normal color vision, the chosen spectra could also enhance color perception in color-deficient observers (Tamura et al. 2015, 2017), and could potentially emulate the effects of filter aids for color deficiencies. We examined the consequences of typical or wide-gamut luminaires for color deficient observers. Protanomalous and deuteranomalous individuals have altered L- or M-cone spectral sensitivities that result in a compression of the color contrasts along the L vs. M axis of cone-opponent space. Light sources designed to increase these contrasts would thus be expected to amplify the L vs. M signals for color-deficient observers. We modeled the effects of different luminaires on color contrast for normal trichromats and protanomalous or deuteranomalous observers. For this we notionally illuminated the spectral reflectances of Munsell surfaces that were selected to yield a uniform circle of 36 hues in a cone-opponent space under an equal energy white luminaire for a color normal trichromatic observer. We then illuminated these surfaces with typical illuminants and the Rec.2020 UHDTV wide color gamut standard to evaluate chromatic contrast for color-anomalous observers and normal trichromats. The results illustrate the potential for modern wide-gamut light sources to enhance color contrast for anomalous trichromats.

Color appearance models use standard color matching functions to derive colorimetric information from spectral radiometric measurements of a visual environment, and they process that information to predict color perceptual attributes such as hue, chroma and lightness. That processing is usually done by equations with fixed numerical coefficients that were predetermined to yield optimal agreement for a given standard observer. Here we address the well-known fact that, among color-normal observers, there are significant differences of color matching functions. These cause disagreements between individuals as to whether certain colors match, an important effect that is often called observer metamerism. Yet how these individual sensitivity differences translate into differences in perceptual metrics is not fully addressed by many appearance models. It might seem that appearance could be predicted by substituting an individual's color matching functions into an otherwise-unchanged color appearance model, but this is problematic because the model's coefficients were not optimized for the new observer. Here we explore a solution guided by the idea that processes of adaptation in the visual system tend to compensate color perception for differences in cone responses and consequent color matching functions. For this purpose, we developed a simple color appearance model that uses only a few numerical coefficients, yet accurately predicts the perceptual attributes of Munsell samples under a selected standard lighting condition. We then added a feedback loop to automatically adjust the model coefficients, in response to switching between cone fundamentals simulating different observers and color matching functions. This adjustment is intended to model long term contrast adaptation in the vision system by maintaining average overall color contrast levels. Incorporating this adaptation principle into color appearance models could allow better assessments of displays and illumination systems, to help improve color appearances for most observers. ispartof: COLOR RESEARCH AND APPLICATION vol:46 issue:4 pages:759-773 ispartof: location:United States status: published

This article discusses the use of light-emitting diodes to generate white light – a research forefront in Physics and Ergonomics. We first present various technological approaches to white-light generation. After a general introduction to the human vision system, we discuss two key aspects of the quality of white light: the color of the light itself, and the color rendering of illuminated objects. We present the tools underlying modern color science, and review key color rendering metrics, from the well-known color rendering index to the latest improvements in the field.

Multi-layer optical thin films can reflect light to guide it along a hollow tube that they internally line. However, reflecting broadband white light for a range of angles requires many precise thin optical layers, which can be too expensive for large-scale applications such as architectural illumination. Here, we present an alternative configuration that requires only one readily achievable aspect of precision—having a substantially constant cross section, perpendicular to the planned longitudinal propagation direction. This aspect conserves a light ray’s longitudinal directional component, while the ray’s path in the perpendicular direction can be macroscopically chaotic, much like the diffuse reflection characteristic arising from many non-absorbing pigment particles. This macroscopic characteristic is described here as “longitudinally specular” and “transversely diffuse.” This new design overcomes two problems that are found with current prism light guides (PLGs), which are a class of hollow light guides that also have a constant cross section. The PLG has two problems: (1) it requires structured surfaces having near-perfect linear prisms that are much larger than the wavelength of light, wasting optical material and increasing absorption; (2) it only works well with light that has been partially collimated, which limits étendue and requires expensive, inefficient input optics. In this paper, a new, to the best of our knowledge, approach, labeled a “multi-layer prism light guide,” simultaneously addresses both problems. Although the new structure is more complex than a conventional PLG, it may be simpler to manufacture. One potential application is for guiding sunlight into buildings for illumination purposes, without requiring complex sun-tracking solar collection optics.

Human vision provides useful information about the shape and color of the objects around us. It works well in many, but not all, lighting conditions. Since the advent of human-made light sources, it has been important to understand how illumination affects vision quality, but this has been surprisingly difficult. The widespread introduction of solid-state light emitters has increased the urgency of this problem. Experts still debate how lighting can best enable high-quality vision—a key issue since about one-fifth of global electrical power production is used to make light. Photometry, the measurement of the visual quantity of light, is well established, yet significant uncertainties remain. Colorimetry, the measurement of color, has achieved good reproducibility, but researchers still struggle to understand how illumination can best enable high-quality color vision. Fortunately, in recent years, considerable progress has been made. Here, we summarize the current understanding and discuss key areas for future study.

We present a method for substantially enhancing the rate of heat transfer into and out of the working fluid of a heat engine, using bidirectional thermal radiation exchange between the external environment and many individual graphene layers that are dispersed and suspended within an inert gas. This hybrid working fluid has the unique composite property of high optical absorption/emission yet low specific heat. Consequently, it can heat and cool rapidly, enabling a much greater cycle frequency and a commensurate increase in specific power, in comparison to conventional closed-cycle heat engines for which the cycle frequency is limited by the use of slower, non-radiative, thermal transfer.

The IES method for evaluating light source color renditionhas the potential to improve how light source spectra are designed and evaluated. The method builds upon decades of color science, amalgamated to create a rational system for evaluating light source color rendition. It can be as simple to use as CIE CRI, or much more powerful thanks to its secondary and tertiary features. Fil: Tonello, Graciela Lucia del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucuman. Instituto de Investigacion En Luz, Ambiente y Vision; Argentina Fil: The society of Light and Lightning.

Recently, a group including the present authors developed a new color rendering (fidelity) measure, approved by the IES and henceforth referred to as IES Rf, that has two major updates with respect to the general color rendering index Ra of the CIE. First, it proposes an update to the more perceptually uniform CAM02-UCS color space. Secondly, instead of using only a small number (eight) of moderately saturated samples to determine a general color fidelity index, the IES method proposes using a set of 99 samples uniformly distributed in color space. In addition to the latter, the sample set has one other important property: spectral uniformity. This ensures that the sample set is not wavelength biased: all wavelengths contribute equivalently to the general color fidelity score. This article explores the importance of these two updates for color fidelity evaluation. It shows how the color space update results in a substantial spread of the new color fidelity scores relative to the old CIE Ra values ...

As displays become larger and more efficient, they may come to provide illumination as well as imagery. This will require reconciling a conflict between color gamut and color rendering. Standards for color rendering are also evolving, and this should be taken into account in the optimization of displays that are intended to serve these two purposes.

For many people, the correct perception of the colors of objects is an important part of life, and today it is being threatened by misinformed policy-making and associated business decisions. Some conservationists and lamp manufacturers have concluded that the accurate color rendering provided by ordinary incandescent lamps is an unaffordable luxury that good citizens should forgo as we employ more energy-efficient alternatives. Though this is not as extreme as suggesting that we should live in cold darkness, it is in the same general direction of deprivation. Yet research has shown that color rendering is important to people and highefficiency lamps can now also provide high color rendering, so there is no longer any need to have lighting that distorts color appearance. This article focuses on the tradeoff between color rendering accuracy and lamp efficiency to show that high color rendering accuracy is appropriate and, contrary to a common misconception, does not intrinsically require greater electrical energy consumption.

© 2019, © 2019 The Illuminating Engineering Society. This article describes a way to distinguish between two distinct components of light source–induced color shifts, base color shift and metameric color shift, to provide a more complete understanding of color rendition. Working within the existing framework of IES TM-30-18 and CIE 224:2017, it shows that base color shift varies smoothly with location in color space in a pattern that is determined by the spectral power distribution (SPD) of the light source. Patterns of smooth variation can often be approximated well with a low-order polynomial function. Here, a vector field model is presented, based on a second-order polynomial function. The polynomial coefficients are adjusted, for a given light source, to provide a least squares fit to the calculated color shifts of a standard set of color samples. The adequacy of this model was verified by comparing it to another approach for characterizing base color shift that is based on discretization of color space and a much larger set of color samples. Once the vector field model of base color shifts for a given light source is determined, the metameric color shifts can be calculated from the residuals and the distribution of those shifts can be statistically summarized. Based on this information, a metameric uncertainty index (R t ) is proposed to provide new information about a light source. In particular, it can be used to estimate the likelihood of noticeable metameric mismatches induced by a given light source, which could lead to improved predictions of the perceived color quality of light. ispartof: Leukos vol:16 issue:2 pages:99-114 status: published

© Illuminating Engineering Society. This tutorial explains how the human perception of color rendering arises, in terms of the underlying phenomena of light and vision, and using those concepts it presents a clear explanation of the CIE Color Rendering Index. The strengths and weaknesses of the CIE Color Rendering Index are reviewed and some common misunderstandings about color rendering are addressed. It is suitable for self-study, with learning outcomes stated at the beginning and a conceptual summary provided at the end. peerreview_statement: The publishing and review policy for this title is described in its Aims & Scope. aims_and_scope_url: http://www.tandfonline.com/action/journalInformation?show=aimsScope&journalCode=ulks20 ispartof: LEUKOS vol:12 issue:1-2 pages:7-26 status: published

Contralateral control, the arrangement whereby most of the human motor and sensory fibres cross the midline in order to provide control for contralateral portions of the body, presents a puzzle from an evolutionary perspective. What caused such a counterintuitive and complex arrangement to become dominant? In this paper we offer a new perspective on this question by showing that in a complex interactive control system there could be a significant net survival advantage with contralateral control, associated with the effect of injuries of intermediate severity. In such cases an advantage could arise from a combination of non-linear system response combined with correlations between injuries on the same side of the head and body. We show that a simple mathematical model of these ideas emulates such an advantage. Based on this model, we conclude that effects of this kind are a plausible driving force for the evolution of contralateral control.

The CIE colour rendering index (CRI) has been criticized for its poor correlation with the visual colour rendering of many spiked or narrowband sources, its outdated colour space and chromatic adaptation transform and the use of a small number of non-optimal reflectance samples that have enabled lamp manufacturers to tune the spectrum of a light source to yield, in some cases, inappropriately high general CRI values. The CRI2012 metric proposed in this paper addresses these criticisms by combining the most state of the art colorimetric colour difference model, i.e. CAM02-UCS, with a mathematical reflectance set that exhibits a highly uniform spectral sensitivity. A set of 210 real reflectance samples has also been selected to provide additional information on the expected colour shifts when changing illumination.

The CIE color rendering (fidelity) index (CRI) has remained unchanged for over four decades.Most, if not all, of its components could be updated to more state-of-the-art methods. One of the most critical components of any color rendering (fidelity) metric is the test sample selection. This article therefore addresses the importance of uniform sampling of wavelength space to avoid selective optimization— that is, taking advantage of the unequal contributions of different wavelength regions to the general color rendering score—of light source spectral power distributions. It summarizes the development of a mathematical sample set with undistorted spectral sensitivity, the HL17 set. The set is used in a recently proposed update, the CRI2012 general color rendering index. To assess the impact of the spectrally uniform sample set on color fidelity scores, the CRI2012 index values for each of a set of 139 lamps were compared with those of the CIE CRI. In addition, the impact of updating the other components was investigated. A mean and maximum absolute difference of respectively 5.9 and 21.8 index units were found between the CRI2012 and CIE CRI, although the largest part—respectively 4.03 and 19.7 index units—was shown to be the result of updating the color difference engine and the switch to the CIE 10◦ observer. The analysis also indicated possible past spectral selective optimization of some warm-white tri-band fluorescent sources for high luminous efficacy of radiation (LER) and (just) sufficient CIE Ra values by taking advantage of the spectral nonuniformity of the CIE reflectance set. Adopting a spectrally uniform sample set in a color rendering metric therefore has important practical implications when designing light source spectra. Finally, possible updates and further improvements of the CRI2012 are briefly mentioned. ispartof: Leukos vol:12 issue:1 pages:61-69 status: published

The question “Why do stars twinkle?” is typically given a superficial answer that satisfies most people. However, as is often the case for physics-related questions about everyday phenomena, a more complete explanation is surprisingly rich and somewhat subtle.

The lighting industry has been increasingly challenged to reduce electrical energy consumption while providing illumination with sufficient color rendering quality. As a result, the problem of accurately assessing color rendering quality has gained increased prominence and the introduction of efficient narrow band light emitting diode (LED) sources has further intensified the debate. This study argues that there is a basic problem with the traditional method of quantifying color quality color rendering index (CRI), one that cannot be solved through minor improvements. The CRI relies on a determination of the degree of color distortion that a test source produces for a small number of test samples of specified spectral reflectance distribution, but there is no clear objective rationale for selecting these few samples. Also, any such arbitrary scoring scheme lacks an objective argument for what constitutes an acceptable score. This study proposes a new method for color rendering assessment that determines the color shift of one thousand, or more, representative reflection spectra that span the full multidimensional range of possible spectral distributions and colors. This broad sampling eliminates the intrinsic selection bias of the CRI calculation and its variants and it is compatible with a more objective standard for a color quality score, one that is statistically based on the fraction of the test spectra that experience color shifts that are less than a just noticeable difference (JND), or an agreed upon multiple of it. Since the concept of JNDs in color has been reproducibly quantified, it is hoped that this approach will be widely acceptable. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2012

Thirty-nine participants viewed six interior scenes in an office/laboratory building and rated them for brightness, uniformity, pleasantness, and glare. The scenes were viewed in three presentation modes: participants saw the real space and images of the spaces on a 17-inch computer monitor in both conventional and high dynamic range (HDR) mode. HDR mode allowed the high range of luminances in the real scene to be accurately reproduced, with maximum luminances more than 10 times higher than those in the conventional images. For those participants who saw the images before the real spaces (the most relevant order for practical applications), the HDR images were rated as significantly more realistic than the conventional images. However, this effect was limited to scenes with relatively large areas of high luminance, which in this study was represented by scenes with windows and daylight. Ratings of the HDR images were significantly related to simple photometric descriptors of the images in the expected manner: Brightness and glare ratings were positively correlated with overall and elevated luminance, and nonuniformity ratings were positively correlated with luminance variability. These results suggest that for evaluations of visual appearance of interior scenes featuring large areas of high luminance, the HDR method may be used as a surrogate for experiencing a real space both for lighting quality research, and in the design process.

The modeling of systems that exhibit near-exponential decay is most commonly done using a sum of exponentials or a stretched exponential. We note some drawbacks of these representations and present an alternative model, the stretched or compressed hyperbola, first described by E. Becquerel in the 1860s. This representation might be more helpful for interpolation, extrapolation, and classification of decays and requires only one additional parameter compared to simple exponential decay.

This paper describes a novel and cost-effective way of providing direct sunlight to the core areas of a multi-storey building. In this system, sunlight is collected by a structure, called the solar canopy illumination system, which attaches to the building directly above the windows on each floor. The sunlight is then redirected by the optical components within the canopy and distributed within the building through a series of special-purpose light guides. These guides pipe the sunlight into the building, and also efficiently incorporate electric light sources so that they can provide supplemental lighting as necessary. This system combines several important energy-saving features and uses components that can be low cost in volume manufacturing. As a result, the system has the potential to be truly cost-effective based on the energy savings. The widespread adoption of such a system could substantially reduce energy consumption worldwide which would make a significant contribution toward greenhouse gas mitigation.

We have developed a system that enables both daylight and electric light to be efficiently delivered to core areas of a building. Daylight is directed into the building by means of a new and cost-effective canopy system which collects sunlight and directs it into the dual-function luminaire. It efficiently transports and distributes the light along its length, and when the amount of daylight is insufficient, auxiliary electric light is automatically provided by fluorescent lamps. This paper focusses on the prototype illumination control system and its performance.

Many real-world scenes contain brightness levels exceeding the capabilities of conventional display technology by several orders of magnitude. Through the combination of several existing technologies, new high dynamic range displays have been constructed recently. These displays are capable of reproducing a range of intensities much closer to that of real environments. We present several methods of reproducing photometrically accurate images on this new class of devices, and evaluate these methods in a perceptual framework.

Digital cinema and home theatre applications need to compete with analog film in terms of image quality. The single most important performance specification of a projection system, and the largest gap in the competition between digital and analog projectors, is the relatively low dynamic range of luminance of current digital projectors. In this paper we introduce a novel digital system capable of displaying images with a high enough dynamic range to rival analog film. The projection system described is based on a serial combination of light modulating devices, such as two liquid crystal micro-display panels within a projection light engine. One of the modulation steps can be of lower spatial resolution and contrast. This increases the optical efficiency of the system and avoids optical artifacts. We describe several hardware implementations of this approach as well as the required image processing. Finally, we present an evaluation of the designs in terms of performance, image quality and cost.

As a component of our cost-effective core daylighting research program, we have developed a hollow light guide that can be used to distribute sunlight collected by a heliostat device, and can also operate as an efficient fluorescent light fixture when the sunlight is insufficient to illuminate the workspace. This dual-function prism light guide structure has a cross-section that is similar to standard commercial fluorescent light fixtures, but with an increased depth in order to pipe the sunlight. The bottom surface of the guide is lined with a thin polycarbonate film having prismatic surface features, while the top and sides are lined with a highly-reflective multilayer optical film having a luminous reflectance greater than 98 percent. The angular constraints of the concentrated sunlight, combined with the high reflectance of the surfaces, enable the sunlight to be efficiently transported within the guide along a distance of greater than 10 m. The guide can also illuminate the room using electri...

Although photometry, the measurement of the intensity and distribution of visible light, is important in many areas, most undergraduate physics courses do not include this topic. We present a simple introduction to key concepts in photometry, and as a fun example, we investigate the optics of a Jack O’Lantern.

Attenuation of light in light guides is a well understood phenomenon from the point of view of the basic underlying physics. Particularly in the case of light guides having a macroscopic cross section, ray trace modeling captures all of the key physics and makes it possible to accurately predict the decay of radiant flux as a function of length in the guide. Unfortunately, in typical applications in the field of illuminating engineering, such calculations are prohibitively difficult for two primary reasons. First, the precise bi-directional reflectance distribution function for the internal surfaces may not be readily available. Second, the precise angular distribution of luminous intensity, as a function of position on the input aperture, may also not be easily quantified. This paper presents a surprisingly simple and accurate general model for describing the flux attenuation with distance in a general light guide. The model has only two free parameters, and therefore measurement of decay at just...

We present a novel means of transporting molecules in solution by applying a zero-time-average alternating motive force to the molecules, and perturbing the molecular drag coefficient synchronously with the applied force, thus causing a net drift in a direction determined by the phase of the alternating drag perturbation relative to the alternating force. We apply an electrophoretic form of the method to transport and concentrate DNA in a gel, such that all molecules migrate on average away from the nearest electrode and toward a central region. Since an electrode does not occupy this central region, this method presents the possibility of transporting and focusing DNA and other charged molecules in regions free from electrodes and the associated electrochemistry.

We are developing a new reflective display technology, based on total internal reflection, which achieves a large difference between the maximum and minimum reflectance values. This yields a surface with greatly improved legibility under a wide range of illumination conditions. Such devices can display an image with a maximum reflectance ranging from 55% under uniform background illumination to over 85% under common non-uniform illumination conditions, even at viewing angles greater than 80° from the surface normal. This approach, which we call ‘CLEAR’ (Charged Liquid Electro-Active Response), uses polymeric microstructures to efficiently redirect incoming ambient light back toward the viewer. One advantage of this technique is the ability to achieve bright, full-color images over a wide range of viewing angles, much like ink printed on paper. The displayed image can be updated rapidly since switching from the reflective state to the absorptive state requires only about a half-micron of motion of absorbing material into the evanescent field associated with TIR. This new approach offers significant advantages in a number of reflective display applications.

The article “White Light” by Mark Rea and Jean Paul Freyssinier is summarized and discussed. The measurement procedure is very promising, and could lead to a variety of significant measurements. However, some of the interpretations presented are problematic. The measurements were based on loci of equal correlated colour temperature, which have neither precise nor consistent physiological or perceptual interpretations, and the resultant conclusions are therefore not uniquely meaningful. Nevertheless, the measurement technique could easily be adapted to slightly different methodologies that could be very powerful, and such replication is highly recommended. © 2012 Wiley Periodicals, Inc. Col Res Appl, 2013

Proteins prefer interfaces, and in aqueous solutions they rapidly adsorb to available solid–liquid interfaces. The adsorption process often involves a change in protein conformation at the surface that can result in functional inactivation of the protein. These changes in protein conformation, which are thought to lead to the formation of an entangled gel-like layer of denatured protein, are responsible for a number of deliterious processes, including biofouling on contact lenses and medical implants. The adsorption process is generally irreversible; dilution of protein in the solution phase does not result in protein desorption from the solid. Presumably, this is due to the effects of the protein denaturation and entanglement process on the rate constant for desorption. Nonspecific protein adsorption to solid–liquid interfaces is, therefore, a kinetically controlled process. Hence, measuring and understanding the kinetics of protein adsorption to solid surfaces, including the kinetics of protein conforma...

We have evaluated a new concept for a variable light valve and thermal insulation system based on nonimaging optics. The system incorporates compound parabolic concentrators and can readily be switched between an open highly light transmissive state and a closed highly thermally insulating state. This variable light valve makes the transition between high thermal insulation and efficient light transmittance practical and may be useful in plant growth environments to provide both adequate sunlight illumination and thermal insulation as needed. We have measured light transmittance values exceeding 80% for the light valve design and achieved thermal insulation values substantially exceeding those of traditional energy efficient windows. The light valve system presented in this paper represents a potential solution for greenhouse food production in locations where greenhouses are not feasible economically due to high heating cost.

As light-emitting diode (LED) light sources mature, lighting designers will be able to deliver white light with a variety of spectral power distributions and a variety of color rendering properties. This experiment examined the effects of three spectral power distributions (SPDs) that were matched in illuminance and chromaticity on three measures of color perception: one objective (performance on the Farnsworth-Munsell 100 hue test) and two subjective (judgments of the attractiveness of one's own skin, and preferences for the saturation of printed images). The three SPDs were a quartz-halogen (QH) lamp and two LED sources that were matched to the QH lamp in terms of both illuminance and chromaticity; the three light sources were nominally CCT = 3500 K, x = 0.40, y = 0.39 and ∼ 400 lx. LED A used three channels (red, green, blue), and had very poor color rendering (Ra = 18). LED B used four channels (red, amber, cyan, white) and had very good color rendering (Ra = 96, whereas the QH had Ra = 98). Secondary hypotheses addressed the effects of age and skin and eye color on the dependent measures. As expected, LED A delivered very different color perceptions on all measures when compared to QH; LED B did not differ from QH. The results show that it is possible for LED sources to match the familiar incandescent sources. However, although it is possible to deliver what appear to be millions of colors with a three-chip (RGB) device, there is the risk of creating a very poor luminous environment. © 2013 National Research Council Canada and Wiley Periodicals, Inc. Col Res Appl, 39, 263–274, 2014; Published Online 12 April 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/col.21811

We investigate the effect of new point spread functions (PSFs) on the uniformity and contrast of high dynamic range displays that use local dimming of LEDs to yield a large dynamic range. A PSF shaped like a quadratic B-spline was hypothesized to create a uniform brightness backlight, as well as producing linear and quadratic gradients, while maintaining a very high contrast. We have found a practical optical structure to produce such a PSF, yielding a nonuniformity of only ±0.8%, while enabling a contrast ratio of 5∶1 and 33∶1 over distances of one and two unit cell spacings, respectively.