LED‐backlit computer screens influence our biological clock and keep us more awake

Abstract— In commodity LC flat‐panel displays, the traditional CCFL backlight is being replaced more and more by LEDs. The typical spectrum of LED‐lit displays shows a significantly higher amount of blue light in the range around 464 nm. Blue light in this wavelength area suppresses the melatonin level in humans and thus effects the biological clock. Our hypothesis was that the amount of blue light reaching the human eye from a LED‐backlit display is sufficient to have a significant effect on the biological clock. The results of clinical user studies comparing the effects of LED‐ vs. CCFL‐backlit displays on humans, resulting from the emitted amount of 464‐nm light, will be presented. It was found that the LED‐backlit display causes significant suppression of melatonin, which effects the biological clock of the test persons, indicating the necessity for displays with a controllable 464‐nm emission. A technical concept for a display with such functionality will be presented.     

Can small shifts in circadian phase affect performance?

Small shifts in circadian timing occur frequently as a result of daylight saving time or later weekend sleep. These subtle shifts in circadian phase have been shown to influence subjective sleepiness, but it remains unclear if they can significantly affect performance. In a retrospective analysis we examined performance on the Psychomotor Vigilance Test before bedtime and after wake time in 11 healthy adults on fixed sleep schedules based on their habitual sleep times. The dim light melatonin onset, a marker of circadian timing, was measured on two occasions. An average 1.1?h shift away from a proposed optimal circadian phase angle (6?h between melatonin onset and midpoint of sleep) significantly slowed mean, median and fastest 10% reaction times before bedtime and after wake time (p?相似文献   

An intensively lit collimating unit for the realization of a mosaic‐structured large‐scale RGB backlight

Abstract— To realize a large‐scale LCD backlight, a hexagon‐shaped single‐side micro‐structured light guide was developed. Three of the micro‐structured light‐guide plates are stacked and combined with a circular prism sheet (CPS) to form a unit backlight. The light guides couple azimuth light radiation from a side‐emitting LED that is mounted at the center of the light guides to air through a CPS in order to make a plane source out of a point source. The combination of stacked functional light guides with a CPS transforms convex toroidal‐shaped light radiation into a narrow cone whose center axis is perpendicular to the back surface of the liquid‐crystal panel. The light efficiency of the illumination unit is about 78% and the full‐width at half maximum of the collimated light is about 2 and 32.5° in the azimuth and radial directions, respectively.     

Wire‐grid polarizers in modern LCOS light‐engine configurations

Abstract— Wire‐grid polarizers that have a very high transmission, reflection, polarized‐light optical performance, and opto‐mechanical packaging advantages compared to the older polarization technologies have been developed. The wire‐grid polarizer operation principles and performance data are reviewed. The power of using finite‐difference time‐domain (FDTD) modeling techniques to understand the interaction of the electromagnetic waves with the wires and improve the optical performance of the wire‐grid polarizers and ultimately the light‐engine optical performance is shown. The ability to ray trace through a complete digital projector light engine from light source to the screen, including the wire‐grid polarizers, will be discussed. The main focus is to present the modern LCOS light‐engine architectures that use the wire‐grid polarizers. One‐, two‐, and three‐panel LCOS light engines are covered.     

Stray light modelling and analysis for the FY‐2 meteorological satellite

Based on the analysis of the mechanism of stray light of the FY‐2 meteorological satellite, the main component of the stray light, generated from the folding mirror direct reflections, is modelled physically. Through the analysis of the stray light outside of the Earth region as well as extracting the high‐order statistical eigenvalues of the designated areas, the stray light function matrix, A, can be calculated using the total least squares (TLS) method, which is applied to the inside of the Earth region, and the full field‐of‐view (FFOV) stray light estimation can be produced efficiently. It is shown that the mean restoration errors of the stray light outside of the Earth region of the infrared (IR), water vapour (WV) and visible (VIS) channels are less than two scaled units, while the visual images are improved greatly. The images of FY‐2B IR with stray light removed and the FY‐2B raw images are inter‐calibrated with the NOAA‐17 Advanced Very High Resolution Radiometer (AVHRR) Ch4 data. The results show that, from 180 to 300?K of the brightness temperature area, the standard deviation of the data with stray light removed is from 1.3 to 3.8?K relative to the NOAA‐17 data, which is improved by 3–10 times in calibration accuracy compared with the raw data inter‐calibration results. The model has been running for testing in the FY‐2B ground operational system and will be applied operationally to the follow‐up satellite system. With the adjustment of a few parameters, the principle of the model can be used for stray light analysis of other instruments on geostationary satellite platform.     

Scalable Realistic Rendering with Many‐Light Methods

Recent years have seen increasing attention and significant progress in many‐light rendering, a class of methods for efficient computation of global illumination. The many‐light formulation offers a unified mathematical framework for the problem reducing the full lighting transport simulation to the calculation of the direct illumination from many virtual light sources. These methods are unrivaled in their scalability: they are able to produce plausible images in a fraction of a second but also converge to the full solution over time. In this state‐of‐the‐art report, we give an easy‐to‐follow, introductory tutorial of the many‐light theory; provide a comprehensive, unified survey of the topic with a comparison of the main algorithms; discuss limitations regarding materials and light transport phenomena and present a vision to motivate and guide future research. We will cover both the fundamental concepts as well as improvements, extensions and applications of many‐light rendering.     

Novel front‐light system using fine‐pitch patterned OLED

Abstract— A novel front‐light system that uses an organic light‐emitting‐diode (OLED) light source patterned with a fine pitch has been developed. The front‐light system has the following characteristics: (1) excellent uniformity within the light‐emitting area; (2) emittance that is consistent at all viewing angles; (3) no light leakage at any viewing angle from the side of the observer. This system can be adopted for reflective LCDs, electrophoretic displays (EPDs), microelectromechanical systems (MEMS), and other applications.     

Raycasting of Light Field Galleries from Volumetric Data

The paper describes a technique to generate high‐quality light field representations from volumetric data. We show how light field galleries can be created to give unexperienced audiences access to interactive high‐quality volume renditions. The proposed light field representation is lightweight with respect to storage and bandwidth capacity and is thus ideal as exchange format for visualization results, especially for web galleries. The approach expands an existing sphere‐hemisphere parameterization for the light field with per‐pixel depth. High‐quality paraboloid maps from volumetric data are generated using GPU‐based ray‐casting or slicing approaches. Different layers, such as isosurfaces, but not restricted to, can be generated independently and composited in real time. This allows the user to interactively explore the model and to change visibility parameters at run‐time.     

Birefringent light‐shaping films for mini‐LED backlights

Birefringent light‐shaping films (BLSFs) for mini‐LED backlit liquid crystal displays (LCDs) are proposed and experimentally demonstrated by passive polymer‐dispersed liquid crystal (PDLC) films. Such films show angle‐selective scattering properties, achieved by proper material engineering and good vertical alignment of liquid crystals. They only respond to angles rather than spatial locations. By directly adhering the BLSF onto a LED, the angular intensity distribution of light can be tailored from Lambertian‐like to batwing‐like. Further simulation proves that by engineering the angular distribution, a fewer number of LEDs or equivalently a shorter light‐spreading distance is required to maintain good uniformity. These BLSFs are expected to find widespread applications in emerging mini‐LED backlit LCDs and shed light on designing other light‐shaping films in the future.     

Direct excitation of xenon by ballistic electrons emitted from nanocrystalline‐silicon planar cathode and vacuum‐ultraviolet light emission

Abstract— To verify the possible use of energetic electrons for direct excitation of inert gas molecules, a nanocrystalline‐silicon (nc‐Si) planar ballistic emitter is operated in a high‐pressure xenon gas ambience. Under the pulse drive, vacuum‐ultraviolet (VUV) light emission is detected without any signs of discharge. The transient behavior of the VUV light emission properly corresponds to that of the nc‐Si emitter. In accordance with quantitative analyses of electron‐emission characteristics and the VUV output, the electron‐to‐photon conversion efficiency reaches 81% in the relatively efficient emitter case. The VUV output power is mainly determined from the number of electrons with energies compatible the with internal excitation of xenon. The emission spectrum observed at a pressure of 10 kPa shows peaks at 152 and 172 nm, which are thought to be originated from metastable Xe²* states. In contrast to the case of conventional impact ionization, no near‐infrared (NIR) peaks are seen in the spectrum. These results strongly suggest that the incidence of energetic electrons causes direct excitation of xenon molecules followed by radiative relaxation through intermediate states. The generated VUV light can be easily converted to visible light using a phosphor screen. As a discharge‐free VUV light emission, this phenomenon is potentially applicable to mercury‐free, high‐efficacy, and high‐stability flat‐panel light‐emitting device.     

Progressive Point‐Light‐Based Global Illumination

We present a physically based progressive global illumination system that is capable of simulating complex lighting situations robustly by efficiently using both light and eye paths. Specifically, we combine three distinct algorithms: point‐light‐based illumination which produces low‐noise approximations for diffuse inter‐reflections, specular gathering for glossy and singular effects and a caustic histogram method for the remaining light paths. The combined system efficiently renders low‐noise production quality images with indirect illumination from arbitrary light sources including inter‐reflections from caustics and allows for simulating depth of field and dispersion effects. Our system computes progressive approximations by continuously refining the solution using a constant memory footprint without the need of pre‐computations or optimizing parameters beforehand.     

Novel direct‐view LED backlight unit with an aspheric microlens array and a rough‐texture sheet

Abstract— This study proposes a novel direct‐view light‐emitting‐diode (LED) backlight unit with a high‐fill‐factor aspheric microlens array and a rough‐texture sheet. An aspheric microlens array and a rough‐texture sheet made from polysiloxine were used as the grating element and optical diffuser, respectively, which increases light‐extraction efficiency and improves luminance uniformity. The specific aspheric microlens‐array mold was fabricated by using a heating encapsulated air process based on a glass wafer. This microlens array has the features of high fill factor and square‐foot boundary with a continuous surface‐relief profile. This unique out‐of‐plane surface profile creates a square light pattern with uniform luminance, and thus composes a uniform large‐sized light pattern exactly in accordance with the layout of the LED array. The rough‐texture sheet, which can scatter light uniformly, was formed by fine‐grit‐sandpaper molding. Experimental results show that by using an aspheric microlens array and rough‐texture sheet reported here as the backlight diffusing components is highly effective in improving light uniformity at a wide viewing angle. An increase in illuminance by more than 10% was achieved in comparison with commercial backlight modules. Low cost in fabricating the aspheric microlens array and rough‐texture sheet is anticipated due to the simplicity of the process.     

Non‐polar‐oriented InGaN light‐emitting diodes for liquid‐crystal‐display backlighting

Abstract— This article addresses spontaneously polarized light emission from GaN‐based light‐emitting diodes (LEDs) fabricated on electrically non‐polar crystallographic orientations and application of spontaneously polarized emission for backlighting of liquid‐crystal displays (LCDs). The first half of the article describes polarized light emission from GaN‐based LEDs and its role in solid‐state lighting technology. The second half reports on our experimental work to explore the potential of non‐polar LEDs for LCD backlighting applications. Optical transmission of non‐polar LED emission was characterized through a liquid‐crystal layer. Extinction ratios of 0.21 were measured between zero and an applied bias voltage to the liquid‐crystal cells. These extinction ratios are not particularly high yet; nevertheless, the experiment has demonstrated the potential of such non‐polar LEDs for LCD backlighting.     

Coded exposure HDR light‐field video recording

Capturing exposure sequences to compute high dynamic range (HDR) images causes motion blur in cases of camera movement. This also applies to light‐field cameras: frames rendered from multiple blurred HDR light‐field perspectives are also blurred. While the recording times of exposure sequences cannot be reduced for a single‐sensor camera, we demonstrate how this can be achieved for a camera array. Thus, we decrease capturing time and reduce motion blur for HDR light‐field video recording. Applying a spatio‐temporal exposure pattern while capturing frames with a camera array reduces the overall recording time and enables the estimation of camera movement within one light‐field video frame. By estimating depth maps and local point spread functions (PSFs) from multiple perspectives with the same exposure, regional motion deblurring can be supported. Missing exposures at various perspectives are then interpolated.     

Laser + LCOS projection‐technology revolution

Abstract— The advent of affordable direct‐diode lasers changes all the rules for optical designs and the associated technologies that generate the images from laser light. These new lasers are forseen as driving fundamental changes in the size, power consumption, cost, resolution, and even the uses for pico‐projectors. This paper discusses these topics from the perspective of laser‐light‐illuminated LCOS microdisplays.     

2‐D FOCON arrays and their application in displays and planar illuminators

Abstract— Focusing cones (FOCON) have been designed for fiber‐optic communication systems as coupling devices. The main aim of these couplers is to match the spatial distribution of the light source or photodetector with the aperture configuration of light‐guiding modes of the optical fibers. In this paper, the application of a 2‐D array of FOCONs for collimating large‐sized optical beams in display devices is proposed. The design of a light‐efficient illumination unit for LCDs that can operate in the reflection mode as a backlight has been demonstrated. The approach proposed is based on the spatial separation of the light propagation in a FOCON array for reflected beams and light that comes from the backlight unit. The application of a FOCON array in backlight units and antiglare coatings has been demonstrated.     

Adaptive BRDF‐Oriented Multiple Importance Sampling of Many Lights

Many‐light rendering is becoming more common and important as rendering goes into the next level of complexity. However, to calculate the illumination under many lights, state of the art algorithms are still far from efficient, due to the separate consideration of light sampling and BRDF sampling. To deal with the inefficiency of many‐light rendering, we present a novel light sampling method named BRDF‐oriented light sampling, which selects lights based on importance values estimated using the BRDF's contributions. Our BRDF‐oriented light sampling method works naturally with MIS, and allows us to dynamically determine the number of samples allocated for different sampling techniques. With our method, we can achieve a significantly faster convergence to the ground truth results, both perceptually and numerically, as compared to previous many‐light rendering algorithms.     

Highly efficient single‐unit white OLED device with emission from both singlet and triplet excitons

We succeeded in developing a single‐unit hybrid organic light‐emitting diode (OLED) device with efficient light emission from both a phosphorescent layer and a fluorescent layer. The single‐unit hybrid OLED achieved a power efficiency higher than that of a two‐unit hybrid tandem OLED with phosphorescent and fluorescent layers.     

Rich‐VPLs for Improving the Versatility of Many‐Light Methods

Many‐light methods approximate the light transport in a scene by computing the direct illumination from many virtual point light sources (VPLs), and render low‐noise images covering a wide range of performance and quality goals. However, they are very inefficient at representing glossy light transport. This is because a VPL on a glossy surface illuminates a small fraction of the scene only, and a tremendous number of VPLs might be necessary to render acceptable images. In this paper, we introduce Rich‐VPLs which, in contrast to standard VPLs, represent a multitude of light paths and thus have a more widespread emission profile on glossy surfaces and in scenes with multiple primary light sources. By this, a single Rich‐VPL contributes to larger portions of a scene with negligible additional shading cost. Our second contribution is a placement strategy for (Rich‐)VPLs proportional to sensor importance times radiance. Although both Rich‐VPLs and improved placement can be used individually, they complement each other ideally and share interim computation. Furthermore, both complement existing many‐light methods, e.g. Lightcuts or the Virtual Spherical Lights method, and can improve their efficiency as well as their application for scenes with glossy materials and many primary light sources.     

Design of a prism light‐guide plate for an LCD backlight module

Abstract— This paper describes the development of a design method for a prism pattern for an LCD light‐guide plate to improve the uniformity of its exiting light. First, the prism surface of the light‐guide plate is divided into several equal regions. With the aid of ASAP simulation, this method uses the mean light flux of all regions as a reference value to adjust the distribution density of the prism pattern for each region. Curve fitting is then performed to provide a smoothly changing distribution density for further improvement of the exiting light uniformity. ASAP results demonstrate that the illuminance uniformity for a 2.5‐in. light‐guide plate is substantially improved from 45% to 90.9% by using this design method.