Non-uniform Luminance Distribution Research Articles

Comparison of luminance distribution on the lighting surface of power LEDs

This work presents luminance distributions across the surface of mid- and high-power diodes. The changes in luminance on diode surfaces following changes in the observation angle were verified. On the basis of the conducted tests, non-uniform luminance distribution on LED surface for diverse observation angles (including the axial direction) was observed. Moreover, it was concluded that luminance changes is not in line with the Lambert’s law. As the result of the research it was also concluded that alterations of the power-supply conditions do not exert any significant impact on the gradient of luminance changes on the surfaces of examined LEDs. Full Text: PDF ReferencesJ. Fan, J. Cao, Ch. Yu, Ch. Qian, X. Fan, G. Zhang, A design and qualification of LED flip Chip-on-Board module with tunable color temperatures, Microelectronics reliability, ISSN 0026-2714, Nº. 84, 2018, pp. 140-148, CrossRef K. Bonislawski, I. Fryc, The study on optical properties of LEDs used for vehicle control lighting, Przeglad Elektrotechniczny, 2012, ISSN 0033-2097, Vol. 88, Issue 3A, pp. 119-120 DirectLink T. Kawabata, Y. Ohno, Optical measurements of OLED panels for lighting applications, Journal of Modern Optics 60(14), 2013, pp. 1176-1186 CrossRef P. Pracki, U. Blaszczak, The issues of interior lighting on the example of an educational building adjustment to nZEB standard, IEEE Lighting Conference of the Visegrad Countries (Lumen V4), IEEE (17 November 2016) CrossRef P. Tabaka, Analysis of electrical parameters of prime set bulb equivalents suitable for dimming, Przeglad Elektrotechniczny, 2015, R. 91, No. 5, pp. 100-106, ISSN 0033-2097 CrossRef D. Czyżewski, The street lighting luminaires with LEDs. Przeglad Elektrotechniczny, 86, 2009, pp. 276-279 DirectLink C. C. Miller; Y. Zong; Y. Ohno, LED photometric calibrations at the National Institute of Standards and Technology and future measurement needs of LEDs, Proc. SPIE Vol. 5530, Fourth International Conference on Solid State Lighting; (2004) CrossRef D. Mozyrska Dorota; M. Wyrwas; I. Fryc, The determination of the LEDs colorimetric parameters, in the range of their operating temperature, Przeglad Elektrotechniczny, Vol. 88, Issue: 4A, 2012, pp. 232-234 CrossRef K. Baran, A. Różowicz, H. Wachta, S. Różowicz, D. Mazur, Thermal Analysis of the Factors Influencing Junction Temperature of LED Panel Sources, Energies, 12, 3941, 2019 CrossRef D. Czyżewski, Research on Luminance Distributions of Chip-On-Board Light-Emitting Diodes, Crystals 9(12), 645, 2019. CrossRef L. Zheng, Z. Guo, W. Yan, Y. Lin, Y. Lu, H.C. Kuo, Z. Chen, L. Zhu, T. Wu, Y. Gao, Research on a Camera-Based Microscopic Imaging System to Inspect the Surface Luminance of the Micro-LED Array. IEEE Access 6, 2018, 51329-51336. CrossRef S. Słomiński, Selected Problems in Modern Methods of Luminance Measurement of Multisource LED Luminaires. Light Eng. 24, 2016, pp. 45-50. DirectLink I. Fryc, P. Jakubowski, K. Kołacz, Analysis of optical radiation parameters of compact discharge HID lamps and LED COB modules used for illuminating shop windows, Przeglad Elektrotechniczny, 2017, R. 93, nr 11, pp. 186-189. CrossRef I. Fryc, Measurement techniques of optical LEDs properties performed with compliance conformity with CIE 127:2007 standard, Przeglad Elektrotechniczny, 2009,ISSN 0033-2097,Vol. 85,Issue:11,pp.317-319. DirectLink I. Fryc, T. Dimitrova-Grekow, An Automated System for Evaluation of the Quality of Light Sources, 2016 IEEE Lighting Conference of the Visegrad Countries (Lumen V4), IEEE (17 November 2016), CrossRef CIE 235:2019, Optical measurement of led modules and light engines, ISBN 978-3-902842-25-1, DOI: 10.25039/TR.235.2019. CrossRef D. Czyżewski, Investigation of COB LED luminance distribution, In Proceedings of the 2016 IEEE Lighting Conference of the Visegrad Countries (Lumen V4), IEEE (17 November 2016) CrossRef I. Rotscholl, K. Trampert; U. Krüger; F. Schmidt, Spectral near field data of LED systems for optical simulations, Proceedings SPIE Volume 11144,Phot. and Educ. in Measur. Sc. 2019, CrossRef

Reliability of diagnosing acute ischemic cerebrovascular on magnetic resonance imaging disorders using iPads.

The use of tablet terminals has been explored in various medical settings; however, caution should be exercised when performing image diagnosis using this technology. The present study examined the characteristics of an iPad Air™ monitor and assessed radiographic image interpretations to verify the reliability of the telediagnosis of acute cerebral infarction based on magnetic resonance imaging (MRI) using a tablet terminal. The luminance of the iPad Air™ was measured using a UA-10 analyzer, and radiographic image interpretation experiments were performed in 100 patients who underwent MRI within 6h of symptom onset. Ten physicians viewed the images on the iPad Air™ and a medical monitor, with an interval of 2months between each interpretation. When the iPad Air™ screen was pure white, the contour lines revealed nonuniform luminance distribution. In the reading experiment, the areas under the curve of the medical monitor and the iPad Air™ were 0.9311 and 0.9431, respectively. No significant difference was observed between the medical monitor and the iPad Air™ (p = 0.113). The results of the observer performance studies for detecting acute ischemic cerebrovascular disorders on an iPad Air™ were found to be similar to those on a medical monitor.

Defining the Actual Luminous Surface in the Unified Glare Rating

ABSTRACTA nonuniform luminance distribution produces more discomfort glare than a uniform one of equal average luminance. Because the standard unified glare rating (UGR) generally considers the average luminance level of the total luminaire surface, its applicability for nonuniform light sources is under discussion. With a growing market share of highly nonuniform light emitting diode (LED) luminaires, a valid discomfort glare metric becomes essential. The UGR can elegantly be improved by discriminating between background and luminous part(s) of a luminaire. A luminance threshold identifies the high-luminance pixels in a luminance map as an actual light emitting surface. Two subjective visual experiments, encompassing commercially available recessed office luminaires and custom-designed luminaires, validate the improved UGR method. With a coefficient of determination of 0.45, the standard UGR fails to predict visual glare sensation. Also covering nonuniform light sources, the improved UGR, with a coefficient of determination of up to 0.91, elegantly ameliorates the visual discomfort calculation from a luminance map.

The effect of spatial luminance distribution on dark adaptation.

Recent studies show that dark adaptation in the visual system depends on local luminance levels surrounding the viewing direction. These studies, however, do not explain to what extent veiling luminance is responsible for the outcome. To address the latter, in this study dark adaptation was measured for three different spatial luminance distributions surrounding a target to be detected, while keeping the veiling luminance at the location of the target equivalent. The results show that a background with bright areas close to the viewing direction yields longer adaptation times than a background with bright areas at a larger visual angle. Therefore, we conclude that dark adaptation is affected to a great extent by local luminance, even when controlling for veiling luminance. Based on our results, a simple but adequate model is proposed to predict the adaptation luminance threshold for backgrounds having a nonuniform luminance distribution.

A Lampshade Design Method by Paper Folding and Luminance Distribution on the Lampshade Designed by the Method. -Skew Quadrilateral Membrane Folding Method-

Historically, Japanese traditional lampstand 'Andon', was manufactured from paper. And paper folding method was adopted into some Andon and western lampshade1). If we put non-flat texture on the surface of such lampshade with paper folding method, nonuniform luminance distribution appears on the surface according to basic laws of illuminance. Such nonuniform luminance on the surface of lampshade contributes to easier recognition of its shape and more attractive appearance. Yoshimura/Diamond pattern2) is one of the most typical paper folding methods in the field of lampshade design. This pattern is known as a structure of crashed cylinder and structure of building roof, and has been made good use in commercial lampshade products1). Yoshimura pattern structure includes a set of skew quadrilaterals which is not on a plane surface and each quadrilateral is constructed by two planar triangles. Consequently, lampshades manufactured with Yoshimura pattern have nonuniform luminance distribution overall, however, luminance distribution within a skew quadrilateral unit is discontinuous at boundary of two planar triangles which compose a skew quadrilateral unit. Author found that similar shape can be constructed by modified Yoshimura pattern and develop the method to ‘Skew Quadrilateral Membrane Folding’ method. In this paper, author indicated principle of the proposed paper folding method at first. In the second, features of the shape made by proposed method and the luminance distribution on the shape are explained. Next, examples of applications of proposed method are indicated. Finally, an example of application of the shape made by proposed method in the field of education is explained.

Inaccuracies Caused by Non-Uniform Luminance Distribution of Artificial Sky Dome at Scale Model Measurements

The primary objective of daylighting measurements, by means of physical models, is the experimental finding of daylight conditions in the interior (in case of scale model of a specific room), or their impact on the surrounding buildings (in case of models of whole buildings). If these measurements are carried out even at the early stage of the building design, they can be very helpful in revealing gross deficiencies of the design or optimization of window apertures. According to the purpose of the measurement, physical models can be placed either on site of the future building – which advantage is the possibility of a reliable reproduction of the actual shading conditions, respectively the amount of reflected light by the envelop of existing buildings – or in laboratory, under artificial sky. The advantage of measurements using artificial skies is mainly the possibility to imitate the conditions of CIE overcast sky, thus the disadvantages of the variability of natural daylight are eliminated, while there is also a potentiality to optimize different solutions at the same boundary conditions. On the other hand, if the luminance distribution of the artificial sky is does not correspond with the theoretical luminance distribution of CIE overcast sky, the results of the measurements can be incorrect. The aim of this contribution is to illustrate through a case study, the importance of ensuring the appropriate boundary conditions at scale model measurements.

Calculation of the Unified Glare Rating based on luminance maps for uniform and non-uniform light sources

In Europe, discomfort glare for interior lighting installations is assessed with the Unified Glare Rating (UGR). UGR is valid for a wide range of uniform light sources but the assessment of discomfort glare from non-uniform luminaires with current glare indices is questioned. LED luminaires often exhibit a non-uniform luminance distribution with alternating areas of high and low luminance. With a growing market share of LED luminaires for interior lighting, a better assessment of discomfort glare from non-uniform light sources becomes essential.In the present paper, the UGR formula is calculated alternatively from the luminance distribution. Individual pixels of a luminance map can be considered as individual light sources or they can be combined to form larger sources. For uniform light sources, the UGR is independent of the division of the luminance map. For non-uniform light sources, the UGR value is strongly dependent on the combination of the individual pixels and differences of up to 17.3 UGR units for the same luminaire are obtained. The UGR calculated from luminance maps is compared with the original UGR from the luminous intensity distribution and the UGR developed for small light sources. In conclusion, the assessment of discomfort glare from non-uniform light sources with UGR calculated from luminance maps is questioned.

Enhancement of Medical Image Details via Wavelet Homomorphic Filtering Transform

AbstractA new medical image enhancement algorithm based on spatial frequency domain is presented in this article. The medical image is first divided into several sub-images based on dyadic wavelet scale analysis. At each level, different directional sub-band images can reflect the different characteristics of the image. A low-frequency sub-band image maintains the original image content information, and high-frequency sub-band images represent image details such as edges and regional boundaries. The corresponding sub-band images are then enhanced by different Butterworth homomorphic filtering functions, which can attenuate the low frequencies and amplify the high frequencies. A linear adjustment is carried out on the low frequency of the highest level. Then, the wavelet reconstruction course is used to obtain the final enhanced image. Experiments on magnetic resonance images of temporomandibular joint soft tissues have shown that the proposed method can effectively eliminate the non-uniform luminance distribution of medical images. Its performance is much better than traditional Butterworth homomorphic filtering algorithm whether in subjective vision quality or objective evaluations such as detailed information entropy and average gradient.

Simulating the spatial luminance distribution of planar light sources by sampling of ray files

Ray files offer a very accurate description of the optical characteristics of a light source. This is essential whenever optical components are positioned in close proximity (near-field) of the light source in order to perform accurate ray tracing simulations. However, a ray file does not allow for a direct simulation of the spatial luminance distribution, i.e. luminance map, by off-the-shelf ray tracers. Simulating luminance maps of light sources or luminaires is especially important in general lighting in order to predict their general perception when viewed by the observer, and more specific, the perception of glare of luminaires having a non-uniform luminance distribution. To enable the simulation of luminance maps while maintaining the high accuracy offered by a ray file, a sampling method is presented. To validate the approach, near-field goniophotometer measurements of two planar light sources were performed. From these measurement data, ray files were extracted to which the sampling method was applied in order to obtain a set of surface sources. This approach was validated by comparing measured luminance images with simulated luminance images. A good agreement was found, validating the presented method.

A prediction method to identify the glare source in a window with non-uniform luminance distribution

A proper glare prediction method is needed to promote visual comfort. The purpose of this study is to suggest the methodology to identify the glare source, which is necessary in order to control glare coming from windows. Experiments with subjects were conducted in order to evaluate discomfort glare from windows and the features that made the subjects recognize the glare sources in the windows with non-uniform luminance distributions were explored. Discomfort glare was evaluated in two categories: first across the whole window and then by unit area of the window. The results of the evaluations led to the realization that the discomfort glare value of the whole window is larger than the mean value of the discomfort glares from the window patches. In addition, it is revealed that the evaluated value of discomfort glare is a function of the average luminance of the visual field. There is a linear relationship between the average luminance of the visual field and the average luminance of the glare patches. Such linear relationship has been translated into a formula, whose high accuracy is proven in the study. Using the formula makes it possible to easily identify the window patches that would generate glare.

The Scope of the Glare Light Source of the Window with Non-uniform Luminance Distribution

This paper presents a methodology to determine the area of the glare light source on the window with nonuniform luminance distribution. Experiments with observers were conducted in order to evaluate discomfort glare using a simulated window with a nonuniform luminance distribution. The simulated window is divided into three parts, each of which has a different luminance so that the window surface would have a non-uniform luminance distribution. Discomfort glare was evaluated in 21 different combinations of the luminance conditions. Hopkinson’s multiple-criterion was used for the evaluation; and 27 observers had volunteered for the test. The results of this study can be used to determine how much the luminance should be in the area around the window in order to reduce discomfort glare from the window. If the luminance around the window was less than 40% of the maximum luminance of the sky seen through the window, this would reduce discomfort glare. If the luminance around the window was higher than 40% of the maximum luminance of the sky seen through the window, the area around the window could be considered as a glare light source.

EFFECTS ON DISCOMFORT GLARE OF LUMINANCE DISTRIBUTION WITHIN A WINDOW

The purpose of this study is to identify discomfort glare from large light sources with non-uniform luminance distribution. The effects of the contrast between luminance of the sky and that of the ground within an artificial window on the evaluation of discomfort glare were experimented on. No significant difference in discomfort glare from the artificial window of the same average luminance with different levels of the skyline was found. The results showed that glare from the source whose luminance contrast ranging from 1/2 to 1/20 can be estimated by average luminance of the source.

Effect of Spatial-Frequency Distribution on Brightness Perception in Light Environment

We conducted a psychophysical experiment using pictures of a light environment as image stimuli. Brightness perception in light environment depends on not only the illumination or mean luminance but also the luminance distribution of the scene. We analyzed the data from the viewpoint of spatial-frequency information processing to estimate the effects of non-uniform luminance distribution on brightness perception. We modified still pictures of scenes of a room (reference images) using two-dimensional frequency analysis. Lowpass-filtering and contrast-gain control operations in the spatial-frequency dimension provided the test images. By adjusting the brightness of the reference images to that of the test images, we derived equi-brightness pairs of the reference and test images. The results showed that even though the mean luminance values of the two images (reference and test stimuli) were equal, the brightness of the lower contrast image was substantially lower and that of the lowpass-filtered image was slightly lower. This suggests that all spatial-frequency channels affect brightness perception and that low spatial-frequency components of non-uniform images are critical factors for increasing brightness.

A first approach to discomfort glare in the presence of non-uniform luminance

This study aims to elucidate the difference in glare sensation between uniform and non-uniform glare sources. In the experiment, the degree of discomfort glare is examined using simulated windows of uniform and non-uniform surface luminance. The window plane is divided into two parts, the upper and lower surfaces, and the luminance and solid angle of each surface are set differently. The upper and lower parts are assumed to be the sky and obstacle, respectively. Two conclusions follow from this study. First, the degree of discomfort glare for the uniform window is higher than it is for the non-uniform window, when the luminance of the uniform window is the same as the average luminance of the non-uniform window. Therefore, the discomfort glare sensation of the non-uniform window is different from that of the uniform window. Second, the glare source in the non-uniform window is restricted by luminance and originates from parts ranging from the highest level of luminance down to a level that is 61% of the highest level of luminance. These results may be useful for selecting the glare source in a window with a non-uniform luminance distribution.

Study of the influence of the dielectric layer thickness in a CNT-FED

An experimental investigation is carried out to study the influences of the dielectric layer thickness variation on the field emission characteristics and luminance distribution in a CNT-FED fabricated by screen-printing. Two steps are contained in the investigation: (1) the dielectric layer thickness fluctuations are presented with an ultrasonic thickness gauge, and (2) a simulation model is constructed to study the corresponding influences of the dielectric layer thickness fluctuations on the field emission characteristics and luminance uniformity on the screen. Our findings indicate that the dielectric layer thickness fluctuations are mainly larger than 5 μm, which mean the dielectric layer thickness fluctuation is an important cause of the non-uniform luminance distribution according to the analysis results from our simulation model. From the simulation results, we also determine the tolerance of the dielectric layer thickness in a CNT-FED to achieve uniform luminance and spot size on the screen.

Quantitative evaluation of “mura” in liquid crystal displays

The visual performance of liquid crystal displays (LCDs) has usually been evaluated by visual inspection during the manufacturing process. One of the visual problems hardest to recognize are regions of low contrast and nonuniform brightness called mura. The accurate and consistent detection of the mura is extremely difficult because there are various shapes and sizes of mura and the inspection results tend to depend on the operators. We conducted a study on the quantitative evaluation of mura based on visual analysis, intending to clarify the detection method and create an automated mura inspection process. We developed an algorithm and a hardware system based on a commercially available charge-coupled-device camera and a personal computer system with an image processor board. This system can successfully identify and evaluate mura. The algorithm was developed from research on visual analysis and human perception. We converted the front-of-screen images from the LCDs into distributions of luminance information, and the mura regions were distinguished from the background area using our novel algorithm. Our identification method can also distinguish between the muras caused by flaws in the LCD cells and the intentionally designed nonuniform luminance distribution of the backlight.

不均一な天井輝度分布をもった大空間 (多目的ドーム) のポールの見え方と背景輝度 (その1)

不均一な天井輝度分布をもった大空間 (多目的ドーム) のポールの見え方と背景輝度 (その1)

不均一な天井輝度分布をもった大空間 (多目的ドーム) のボールの見え方と背景輝度 (その2)

不均一な天井輝度分布をもった大空間 (多目的ドーム) のボールの見え方と背景輝度 (その2)

カラーブラウン管の発光特性に起因する測光誤差

A generalized method of predicting photometric error sources due to the light emitting properties of the light source to be measured, is proposed. This method is based on a comparison of the radiant energy distributions of both test and standard sources on each axis in the space that characterizes the light emitting properties. As a result of applying this method to luminance measurement of color TV picture tubes, the following are determined to be error sources: (1) unusual spectral power distribution, (2) non-uniform luminance distribution over a phosphor screen, (3) deviation from the perfect diffusion, and (4) pulsed light due to electron beam scanning. Quantitative error analysis for a typical measurement shows that photometric errors due to the above sources are 2.6%, 0.1%, 1% and 2%, respectively.

The transmission of diffuse light by a sloping roof

A method of calculating the diffuse light transmission of sloping transparent roofs is given and the results of such calculations are compared with experimental measurements on acrylic sheet. The need to recognize the non-uniform luminance distribution of the light from an overcast sky is demonstrated; it is also shown that light reflected from the underside of a pitched roof makes a significant contribution to the total illumination.