Luminance Values Research Articles

Pixelated phosphors for high-resolution and high-contrast white light sources: erratum.

Erroneous absolute luminance values of the pixelated phosphor structure B25 (pixel size of 25 microns by 25 microns) have been corrected. The updated figure shows clearly the potential of the investigated structure as light-converter for high-resolution lighting systems.

Research Note: The measurement of road lighting with developed artificial intelligence software

Road lighting needs to be measured at regular time intervals. In this way, new road lighting projects can be controlled in compliance with the specifications, and existing road lighting luminaires that are damaged or of reduced efficiency can be identified and replaced. Today, lighting measurements are mostly made by using hardware tools that make point measurements. The use of this method requires expert staff, money and time. In this pilot study, artificial intelligence and web-based software were developed to make road lighting measurements using photographs of roads. For this purpose, reference points have been determined on the road. The correlation between luminance values and pixel values of these points was established using artificial intelligence techniques. Artificial neural networks, fuzzy logic and adaptive neuro fuzzy inference system methods are used to establish the correlation. With this software, the difficulties encountered when using the conventional measurement method are reduced; road lighting measurements can be done in a short time, cost-free and online.

Evidence for a common mechanism of spatial attention and visual awareness: Towards construct validity of pseudoneglect.

Present knowledge of attention and awareness centres on deficits in patients with right brain damage who show severe forms of inattention to the left, called spatial neglect. Yet the functions that are lost in neglect are poorly understood. In healthy people, they might produce “pseudoneglect”—subtle biases to the left found in various tests that could complement the leftward deficits in neglect. But pseudoneglect measures are poorly correlated. Thus, it is unclear whether they reflect anything but distinct surface features of the tests. To probe for a common mechanism, here we asked whether visual noise, known to increase leftward biases in the grating-scales task, has comparable effects on other measures of pseudoneglect. We measured biases using three perceptual tasks that require judgments about size (landmark task), luminance (greyscales task) and spatial frequency (grating-scales task), as well as two visual search tasks that permitted serial and parallel search or parallel search alone. In each task, we randomly selected pixels of the stimuli and set them to random luminance values, much like a poor TV signal. We found that participants biased their perceptual judgments more to the left with increasing levels of noise, regardless of task. Also, noise amplified the difference between long and short lines in the landmark task. In contrast, biases during visual searches were not influenced by noise. Our data provide crucial evidence that different measures of perceptual pseudoneglect, but not exploratory pseudoneglect, share a common mechanism. It can be speculated that this common mechanism feeds into specific, right-dominant processes of global awareness involved in the integration of visual information across the two hemispheres.

A Spiking Neural Network Model of Depth from Defocus for Event-based Neuromorphic Vision

Depth from defocus is an important mechanism that enables vision systems to perceive depth. While machine vision has developed several algorithms to estimate depth from the amount of defocus present at the focal plane, existing techniques are slow, energy demanding and mainly relying on numerous acquisitions and massive amounts of filtering operations on the pixels’ absolute luminance value. Recent advances in neuromorphic engineering allow an alternative to this problem, with the use of event-based silicon retinas and neural processing devices inspired by the organizing principles of the brain. In this paper, we present a low power, compact and computationally inexpensive setup to estimate depth in a 3D scene in real time at high rates that can be directly implemented with massively parallel, compact, low-latency and low-power neuromorphic engineering devices. Exploiting the high temporal resolution of the event-based silicon retina, we are able to extract depth at 100 Hz for a power budget lower than a 200 mW (10 mW for the camera, 90 mW for the liquid lens and ~100 mW for the computation). We validate the model with experimental results, highlighting features that are consistent with both computational neuroscience and recent findings in the retina physiology. We demonstrate its efficiency with a prototype of a neuromorphic hardware system and provide testable predictions on the role of spike-based representations and temporal dynamics in biological depth from defocus experiments reported in the literature.

The effect of luminance values of the edge between regions on figure-ground perception.

The present study examined whether luminance values of an edge between regions affect figure-ground perception. A dark-gray or light-gray region was presented on the left (or upper) or right (or lower) side of an edge. Observers reported which region was perceived as a figure. The results in the 0.2° edge width condition showed that dark-gray regions with low luminance edges were perceived as a figure significantly more often than dark-gray regions with high luminance edges. The edge luminance effect occurred, partly occurred, and did not occur when the edge widths were 0.2, 0.5, and 0.8° of visual angle, respectively. These results showed that luminance values of the edge between the regions affected figure-ground perception, and that regions with luminance values closer to that of the edge between the regions were perceived as a figure more often, but only when the edge width was narrow. The edge luminance effect occurred less often as the edge width was increased and would be attributed to similarity grouping between edge and region.

White Light-Emitting Devices Based on Inorganic Perovskite and Organic Materials.

Perovskite-based materials have attracted considerable attention in photoelectric devices. In this paper, we report the one-step fabrication of spin-coated CsPbBr2.5I0.5 perovskite films doped with PAN (polyacrylonitrile) polymer. A red perovskite LED (PeLED) composite film was fabricated which featured a maximum luminance value of 657 cd/m2 at 8 V. We fabricated white PeLEDs by combining hole transporting layer material emission, perovskite–polymer composite material PAN:CsPbBr2.5I0.5, and pure inorganic perovskite CsPbBr3 as a luminescent layer. The maximum luminance of the device was 360 cd/m2 at 7 V, and the color coordinate was (0.31, 0.36). We obtained an ideal white light-emitting device that paves the way for further development of white PeLEDs.

Single-Component Color-Tunable Gd(pic)3: Eu3+ Phosphor Based on a Metal-Organic Framework for Near-UV White-Light-Emitting Diodes.

Compared with their multicomponent analogues, single-component white-light-emitting diodes (WLEDs) can eliminate the disadvantages such as high cost, fluorescence self-absorption, poor machinability, and reproducibility, but how to produce white light with high quality in a single-phase host is still a big challenge. In the work, a series of Eu3+/Tb3+-doped Gd(pic)3 and La(pic)3 are obtained through solvothermal conditions with picolinic acid (Hpic) and lanthanide nitrate. Researchers could regularly modulate the emitting color of phosphors by adjusting the excitation wavelength as well as the relative concentration of Ln3+ ions to obtain white light. Different luminance values [especially quantum yield (QYs)] between host materials Gd(pic)3 and La(pic)3 are investigated, which shows that doping of Eu3+ into Gd(pic)3 can improve QY to a great extent. By employing Gd0.9512Eu0.0488(pic)3 and Gd0.9141Eu0.0451Tb0.0408(pic)3 as phosphors, we successfully fabricated two excellent near-ultraviolet (365 nm) WLEDs with CIE chromaticity coordinates (0.3052, 0.3462) and (0.3007, 0.3448), relatively low color-correlated temperature (6755, 7001 K), and high color rendering index (Ra = 71.8, 72.9). This approach may open a new prospect for developing single-phase near-ultraviolet phosphors with high efficiency.

Development of Sky Luminance and Daylight Illuminance Prediction Methods for Lighting Energy Saving in Office Buildings

Accurately predicting indoor illuminance from daylight during the early stages of building design is an important factor in saving energy and the costs associated with lighting. The objective of this study was to predict sky luminance distribution using the Commission Internationale de l’éclairage (CIE) standard sky model, and propose a method that can be used to predict indoor illuminance. Results obtained from the proposed prediction method were compared and verified with simulation values obtained by Desktop Radiance. From the CIE overcast sky, the zenith/horizon ratio was 3:1. From the CIE clear sky, the luminance value was highest around the sun. In contrast, the luminance value was lowest in the opposite direction of the sun when the angle between the sun and sky elements was 90°. In addition, this study suggested an indoor illuminance prediction method by applying the effects of sky luminance, direct sunlight, and wall reflection elements. When the proposed equation’s calculation results were compared with Desktop Radiance simulation’s value in overcast and clear sky, all statistically analysis (R2, MBE, Cv(RMSE), t-value, p-value) satisfied each standard and showed high correlations. Consequently, it was established that the predicted indoor illuminance obtained from the proposed prediction method was accurate and can be used to predict the level of indoor illuminance. The results further revealed that it is possible to calculate indoor illuminance when installing blinds, by substituting variable values of visible light transmittance (VLT).

Al2O3-Ce:GdYAG composite ceramic phosphors for high-power white light-emitting-diode applications

In order to meet the increasing demand of high-power light-emitting-diode (LED) lighting, state-of-the-art white light-emitting diode technology needs phosphors with high thermal conductivity and high luminous efficacy as color converters. In this work, translucent Al2O3-Ce:GdYAG composite phosphors were prepared by solid-state reactive sintering. The microstructure shows that the Al2O3 particles are uniformly dispersed in the Ce:GdYAG matrix. These particles can not only improve the thermal conductivity of the ceramics, but also promote the extraction efficacy. The luminous characteristics of the Ce:GdYAG and Al2O3-Ce:GdYAG ceramics were analyzed after being packaged with blue LED. When the molar ratio of Al2O3/Ce:GdYAG is 0.8, a high luminous efficacy value of 112.6 lm/W is achieved by the Al2O3-Ce:GdYAG composite ceramic phosphor with the thickness of 0.4 mm, as well as the highest CRI valve of 71.4. The appropriate photoelectric properties of this kind of ceramic phosphor make it a promising candidate for high-power LED device.

Color retinal image enhancement using luminosity and quantile based contrast enhancement

Retinal imaging is used to diagnose common eye diseases. But retinal images that suffer from image blurring, uneven illumination and low contrast become useless for further diagnosis by automated systems. In this work, we have proposed a new method for overall contrast enhancement of the color retinal images. Initially, a gain matrix of luminance values which is obtained by adaptive gamma correction method is used to enhance all three color channels of the images. After that quantile-based histogram equalization is used to enhance overall visibility of the images. Enhancement results of the proposed method are compared with several other existing methods. Performance of the proposed method is evaluated on all images of publicly available Messidor database. Based on the assessment measure we have shown that the proposed method is able to enhance the contrast of given color retinal image without changing its structural information. The proposed technique is appeared to accomplish superior image enhancement with sufficient contrast enhancement, these enhancement results are better than other related techniques. This technique for color retinal image enhancement might be utilized to help ophthalmologists in the more productive screening of retinal ailments, what’s more, being developed of enhanced robotized image examination for clinical finding.

Vector Multilevel Tone-Dependent Error Diffusion in the YyCxCz Color Space

In this paper, we present a tone-dependent fast error diffusion algorithm for color images, in which the quantizer is based on a simulated linearized printer space and the filter weight function depends on the ratio of the luminance of the current pixel to the maximum luminance value. The pixels are processed according to a serpentine scan instead of the classic raster scan. We compare the results of our algorithm to those achieved using the fixed Floyd-Steinberg weights and processing the image according to a raster scan ordering.

The Intestinal Microbiota of Hermetia illucens Larvae Is Affected by Diet and Shows a Diverse Composition in the Different Midgut Regions.

The larva of the black soldier fly (Hermetia illucens) has emerged as an efficient system for the bioconversion of organic waste. Although many research efforts are devoted to the optimization of rearing conditions to increase the yield of the bioconversion process, microbiological aspects related to this insect are still neglected. Here, we describe the microbiota of the midgut of H. illucens larvae, showing the effect of different diets and midgut regions in shaping microbial load and diversity. The bacterial communities residing in the three parts of the midgut, characterized by remarkable changes in luminal pH values, differed in terms of bacterial numbers and microbiota composition. The microbiota of the anterior part of the midgut showed the highest diversity, which gradually decreased along the midgut, whereas bacterial load had an opposite trend, being maximal in the posterior region. The results also showed that the influence of the microbial content of ingested food was limited to the anterior part of the midgut, and that the feeding activity of H. illucens larvae did not significantly affect the microbiota of the substrate. Moreover, a high protein content compared to other macronutrients in the feeding substrate seemed to favor midgut dysbiosis. The overall data indicate the importance of taking into account the presence of different midgut structural and functional domains, as well as the substrate microbiota, in any further study that aims at clarifying microbiological aspects concerning H. illucens larval midgut.IMPORTANCE The demand for food of animal origin is expected to increase by 2050. Since traditional protein sources for monogastric diets are failing to meet the increasing demand for additional feed production, there is an urgent need to find alternative protein sources. The larvae of Hermetia illucens emerge as efficient converters of low-quality biomass into nutritionally valuable proteins. Many studies have been performed to optimize H. illucens mass rearing on a number of organic substrates and to quantitatively and qualitatively maximize the biomass yield. On the contrary, although the insect microbiota can be fundamental for bioconversion processes and its characterization is mandatory also for safety aspects, this topic is largely overlooked. Here, we provide an in-depth study of the microbiota of H. illucens larval midgut, taking into account pivotal aspects, such as the midgut spatial and functional regionalization, as well as microbiota and nutrient composition of the feeding substrate.

Calculation of Mesopic Luminance Using per Pixel S/P Ratios Measured with Digital Imaging

ABSTRACT This study describes a method of measuring the pixelwise S/P ratio using a calibrated digital camera and applying these S/P ratios to calculate mesopic luminance values. An example of using the developed method is presented. Further improvements for the method are discussed.

Do users perceive the same image differently? Comparison of OLED and LCD in mobile HMDs and smartphones

ABSTRACTThe two leading panel types in the current smartphone market are OLED (organic light-emitting diode) and LCD (liquid crystal display). Even though OLED is known to show more vivid and brighter colors, however, LCD is still dominant in the market. In the rising era of HMDs (head-mounted displays), the present study examined which panel the consumers prefer in the smartphone and HMD context by investigating the characteristics of panels as perceived by the consumers as well as the consumers’ VR (virtual reality) material preferences. The characteristics of the different panels as perceived by the consumers were extracted, and the users’ VR material preferences were ranked. The study findings indicate that OLED should be used for HMDs to increase the consumers’ satisfaction. Furthermore, the users did not find any significant difference between the two different luminance values of the OLED panel that was used for the study, which indicates that the luminance of the panel can be optimized for a comfortable and satisfying HMD viewing setting.

A Better Photometric Index of Photo-Biological Effect on Visual Function of Human Eye: Illuminance or Luminance?

The illuminance index has been widely used in the field of photometry, although the luminance contains more information on not only light intensity but also light direction. In this study, we clarify which photometric index is more competent to describe the influence of lighting environment on human eye. In this study, we propose a novel methodology to investigate the photo-biological effect of the lighting environment by human factor experiment. With the human factor experiments performed on 20 participants, we compare the variations of ocular responses during the Landolt-rings-counting visual task in lighting environments with similar illuminance while distinct luminance changes. With the same Correlated Color Temperature (CCT) and Spectral Power Distribution (SPD), optical performances with similar illuminance values present quite different influences on ocular responses, and the response variations are found to vary with luminance values. It is implied that the regularity of luminance influence on the ocular responses to lighting environment is likely to be dependent on luminance value instead of illuminance, and the photometric index luminance seems more appropriate to be used to assess the lighting quality in standards.

Embedded Microcontroller with a CCD Camera as a Digital Lighting Control System

Although with the advent of the LEDs the energy consumption in buildings can be reduced by 50%, there exists a potential for energy savings due to lighting controls. Moreover, lighting controls can ensure that the near zero energy requirements by EU can be achieved for near zero energy buildings (nZEBs). For this reason, more sophisticated lighting controls must be proposed in order to take full advantage of LEDs and their flexibility concerning dimming. This paper proposes the architecture of an embedded computer camera controller for monitoring and management of image data, which is applied in various control cases, and particularly in digitally controlled lighting devices. The proposed system deals with real-time monitoring and management of a GigE camera input. An in-house developed algorithm using MATLAB enables the identification of areas in luminance values. The embedded microcontroller is part of a complete lighting control system with an imaging sensor in order to measure and control the illumination of several working areas of a room. The power consumption of the proposed lighting system was measured and was compared with the power consumption of a typical photosensor. The functional performance and operation of the proposed camera control system architecture was evaluated based upon a BeagleBone Black microcontroller board.

Photometric and Electrical Characterizations of Large-Area OLEDs Aged Under Thermal and Electrical Stresses

The aim of this paper is to identify the electrical signatures of degradations of large-area organic light-emitting diodes (OLEDs) (41 cm² active area), subjected to various stress conditions. Three Philips GL55 OLEDs were stressed under three distinct temperature values: 23 °C, 40 °C, and 60 °C at a stress current density of J = 15 mA/cm² (rated current density: Jn = 9.49 mA/cm²). Under thermal and electrical stresses, an increase of the operating voltage was observed with stress time but thermal stress alone did neither affect the operating voltage nor the luminance values up to 60 °C.

Visual Impairment, Adaptation Luminance, and Glare: An Empirical Investigation

Visually impaired people primarily rely on their remaining vision. Unfavorable lighting conditions can further hamper this remaining vision. In this context, the present contribution mainly focuses on the evaluation of the visual performance of visually impaired and normally sighted individuals under different lighting conditions. To investigate the visual performance empirically, we developed a test involving different adaptation luminance values. A monitor with adjustable brightness facilitated various tests to determine the visual performance as a function of the adaptation luminance and glare. In addition, the subjective impressions of the visually impaired participants were captured via interviews. The study included 98 visually impaired people and 38 people without eye-related ailments. The interview results suggest that most people with visual disabilities require special lighting conditions. An increased lighting requirement is observed amongst 50% of this group. Moreover, 75% of this group display increased glare sensitivity. Likewise, adaptation problems and critical issues related to non-uniform lighting are manifest. Visually impaired individuals display significant in the visual performance variance at different brightness levels. Individuals with eye disease display a greatly reduced contrast threshold and a higher subjective level of discomfort compared to individuals with normal vision. Most visually impaired individuals require a higher degree of brightness to achieve their maximum personal visual performance. About a quarter of these individuals achieves the optimal visual performance at lower brightness, while displaying an increased sensitivity to glare. In general, glare has a decisive influence on the visual performance of visually impaired people. For general lighting purposes, a predominantly indirect lighting source better accommodates these individuals' requirements.

Edge Detection With Chroma Components of Video Frame Based on Local Autocorrelation

Edge feature extraction is an important basis part for subsequent processing of video frame. The region with a small color difference is transformed into a luminance value for edge detection, which increases the difficulty of edge detection and reduces the detection accuracy. In order to improve the precision of edge detection in the regions with small color difference, local autocorrelation is proposed to enhance the edge feature. Edge detection is completed by using chroma information, and the detection rate is used to measure the extent of the detected edge of the ideal edge to be extracted. The input video frame is converted to YCbCr color mode, and local autocorrelation is applied to the luminance information Y and chroma information Cb for edge detection. Complementary processing is applied to the resulting image of edge detection based on local autocorrelation. In order to further improve the detection rate, supplementary processing is carried out. The standard edge images are defined for quantitative analysis and evaluation of proposed methods. Two kinds of edge correction processing based on the local autocorrelation comparison method and average method are proposed. Through experimental verification, the comparison method has a higher detection rate than the common method on the basis of local autocorrelation.

Effect of high thermal stress on the organic light emitting diodes (OLEDs) performances

The configuration of an organic light emitting diode (OLED) that combines different types of material to form a complete, functional device has induced an interlayer stress. This situation can further affect the performances of OLED, especially under high-temperature conditions as regards to different values of the thermal expansion coefficient (CTE) between the layers. Hence, this paper presents the thermal behavior of OLEDs under such conditions specifically in non-operated mode (no electrical current is given during the experiment). A batch of commercially available OLEDs has been employed. They were exposed to several temperatures in a controlled oven, including temperatures that higher than the glass transition temperature (Tg) limit of the polymer material (∼126 ℃). It was observed that the luminance value had dramatically dropped by 90% from the initial value after the OLEDs were stressed at 135 ℃, whereas the voltage-drop greatly escalated from 8.5 V to 30.2 V. Via FIB-FESEM analysis, the presence of voids (layer mismatch) was evident due to interfacial thermal stress imparted between the layers. The voids had allowed the infiltration of moisture and oxygen into the device and eventually led to the formation of bubble-like defects on top of the cathode’s surface. This condition has resulted in deterioration of electrons injection path and permanently changed the morphological structures of the devices. Through calculations, it was verified that the interfacial thermal stress between the layers reduced about 50% as the thickness of the polymer layer was increased by two times of its initial dimension.