Search Results (15)

High-power-density LED devices have emerged as a prominent focus in current research and industrial development, largely due to their role in advancing LED lighting technologies. At high power and high current, the structure and area of the thermoelectrically separated copper substrate connected to the LEDs significantly influence the device’s optoelectronic performance, yet detailed studies in this area remain limited. To address this issue, blue and white LED devices with a maximum power rating of 400 W were fabricated and soldered onto copper substrates with diameters of 20 mm, 25 mm, and 32 mm. The influence of substrate area on the I–V and I–L characteristics of the LEDs was systematically measured and analyzed at different operating temperatures. Additionally, variations in operating voltage and luminous intensity with temperature were investigated under specific driving currents. Infrared thermal imaging was employed to examine the thermal field distribution under varying substrate sizes and current levels. The results show that increasing the copper substrate diameter from 20 mm to 25 mm and further to 32 mm leads to a significant improvement in LED optoelectronic performance. To determine the diameter threshold beyond which performance gains diminish, a 3D COMSOL 6.1. model was developed. The model reveals that expanding the diameter from 32 mm to 35 mm results in only a marginal improvement, while further increasing it to 40 mm offers a negligible additional benefit, thereby identifying the optimal substrate area for performance saturation. Full article

See-through augmented reality glasses, such as HoloLens 2, are increasingly adopted in medical settings; however, their efficacy as medical display devices remains unclear, as current evaluation protocols are designed for traditional monitors. This study examined whether the established display-evaluation techniques apply to HoloLens 2 and whether it meets standards for primary and secondary medical displays. HoloLens 2 was assessed for overall image quality, luminance, grayscale consistency, and color uniformity. Five participants rated the TG18-OIQ pattern under ambient lighting conditions of 2.4 and 138.7 lx. Minimum and maximum luminance were measured using the TG18-LN12-03 and -18 patterns, targeting ≥ 300 cd/m² and a luminance ratio ≥ 250. Grayscale conformity to the standard grayscale display function allowed deviations of 10% for primary and 20% for secondary displays. Color uniformity was measured at five screen positions for red, green, and blue, with a chromaticity limit of 0.01 for primary displays. HoloLens 2 satisfied four of the ten primary and four of the seven secondary overall-quality criteria, achieving a maximum luminance of 2366 cd/m² and a luminance ratio of 1478.75. Grayscale uniformity was within tolerance for 10 of the 15 primary and 13 of the 15 secondary measurements, while 25 of the 30 color uniformity values exceeded the threshold. The adapted evaluation methods facilitate a systematic assessment of HoloLens 2 as a medical display. Owing to inadequate grayscale and color representation, the headset is unsuitable as a primary diagnostic display; for secondary use, requirements must be assessed based on specific application requirements. Full article

Endoscopes are crucial for assisting in surgery and disease diagnosis, including the early detection of cancer. The effective use of endoscopes relies on their optical performance, which can be characterized with a series of metrics such as resolution, vital for revealing anatomical details. The modulation transfer function (MTF) is a key metric for evaluating endoscope resolution. However, the 2020 version of the ISO 8600-5 standard, while introducing an endoscope MTF measurement method, lacks empirical validation and excludes opto-electronic video endoscopes, the largest family of endoscopes. Measuring the MTF of video endoscopes requires tailored standards that address their unique characteristics. This paper aims to expand the scope of ISO 8600-5:2020 to include video endoscopes, by optimizing the MTF test method and addressing parameters affecting measurement accuracy. We studied the effects of intensity and uniformity of image luminance, chart modulation compensation, linearity of image digital values, auto gain control, image enhancement, image compression and the region of interest dimensions on images of slanted-edge test charts, and thus the MTF based on these images. By analyzing these effects, we provided recommendations for setting and controlling these factors to obtain accurate MTF curves. Our goal is to enhance the standard’s relevance and effectiveness for measuring the MTF of a broader range of endoscopic devices, with potential applications in the MTF measurement of other digital imaging devices. Full article

Luminance measurements are the least frequent of all photometric measurements. This article characterizes and systematizes the various methods of luminance measurement. In particular, the method of direct luminance measurement using modern luminance meters (ILMD) is described in detail. This paper presents the results of the study on the influence of the measurement distance on the luminance measurement results. Two ILMD meters (laboratory and portable) and a luminance standard were used in this study. The conducted research showed that an incorrectly chosen measuring distance can lead to significant measurement errors of up to several tens of percent. In addition, the possible impact of incorrect measurements on the design of an interior lighting installation was presented. It was shown that the selected interior lighting installation can consume more than 40 percent more electricity compared to the installation based on the correct luminance measurements of the luminaires with diffuse shades. In the final stage of the study, the definition of the photometric test distance for luminance measurements using ILMD was proposed. The test results can be particularly useful for the luminance measurements of OLEDs or the luminaires with diffuse luminous character. However, these results can also be used for luminance measurements of other light sources and luminaires. Full article

Luminance maps are information-dense measurements that can be used to directly evaluate and derive a number of important lighting measures, and improve lighting design and practices. However, cost barriers have limited the uptake of luminance imaging devices. This study presents a low-cost custom luminance imaging device developed from a Raspberry Pi microcomputer and camera module; however, the work may be extended to other low-cost imaging devices. Two calibration procedures for absolute and relative luminance are presented, which require minimal equipment. To remove calibration equipment limitations, novel procedures were developed to characterize sensor linearity and vignetting, where the accurate characterization of sensor linearity allows the use of lower-cost and highly non-linear sensors. Overall, the resultant device has an average absolute luminance error of 6.4% and an average relative luminance error of 6.2%. The device has comparable accuracy and performance to other custom devices, which use higher-cost technologies and more expensive calibration equipment, and significantly reduces the cost barrier for luminance imaging and the better lighting it enables. Full article

The technique most widely used to quantitatively measure leg edema is only a pitting edema method. It has recently become possible to digitize B-mode ultrasound images and accurately quantify their brightness using an image-analysis software program. The purpose of this study was to find new indices of the grade of leg skin, to study whether or not analyses of the subcutaneous layer of leg skin on ultrasound images using image-editing software program can be used to evaluate it and to digitize it. Images of 282 subcutaneous layers of leg skin in 141 pregnant women were obtained using a B-scan portable ultrasound device. Rectangular photographs (vertical: skin thickness; horizontal: width of probe) were obtained using an image-editing program, and the luminous intensity (pixel grayscale: 0–255) and thickness of the skin were calculated using a histogram. We investigated the correlation between these parameters and the grade of pitting edema (0–3). There was a significant positive correlation between the grade of pitting edema and the average luminous intensity value, its standard deviation, and the skin thickness (ρ = 0.36, ρ = 0.22, ρ = 0.51, p < 0.0001, respectively). In particular, there was strong positive correlation between the grade of pitting edema and both the total number of pixels in a rectangle × (multiplied by) the average luminous intensity value and the total number of pixels in a rectangle × the standard deviation of the average luminous intensity value (ρ = 0.58 and ρ = 0.59, p < 0.0001, respectively). We could quantitatively evaluate the grade of leg edema by analyzing ultrasound photographs of the subcutaneous layer of the leg skin using an image-editing software program and found new indices to digitize it. Full article

Over the last few years, light-emitting diodes have completely dominated the lighting field. In road lighting, high-power LEDs have replaced traditional light sources. That is why various technical aspects of LEDs have been researched extensively worldwide. However, little research has been conducted in the area of luminance measurement. This paper reviews the methods for measuring the luminance of high-power LEDs. Particular attention is paid to the influence of the measurement distance on the measurement results. Next, the results of the tests using a modern image luminance measuring device (ILMD) for luminance measurements are presented. It is concluded that it is necessary to redefine the photometric test distance. The conducted research demonstrates that an incorrectly selected test distance can lead to the huge errors of several hundred per cent or more. In addition, the possible impact of the incorrect measurements on the design of road lighting installations is presented. It is shown that a road lighting installation can use over 300% more electrical energy compared to the installation based on the correct luminance measurements of single LEDs. In the final stage of the research, the definition of the photometric test distance for LED measurements using ILMD is proposed. The results of the research can also be useful for the luminance measurements of other types of LEDs. Full article

There are several tools and methods to quantify light pollution due to direct or reflected light emitted towards the sky. Unmanned aerial vehicles (UAV) are still rarely used in light pollution studies. In this study, a digital camera and a sky quality meter mounted on a UAV have been used to study the relationship between indices computed on night images and night ground brightness (NGB) measured by an optical device pointed downward towards the ground. Both measurements were taken simultaneously during flights at an altitude of 70 and 100 m, and with varying exposure time. NGB correlated significantly both with the brightness index (−0.49 ÷ −0.56) and with red (−0.52 ÷ −0.58) and green band indices (−0.42 ÷ −0.58). A linear regression model based on the luminous intensity index was able to estimate observed NGB with an RMSE varying between 0.21 and 0.46 mpsas. Multispectral analysis applied to images taken at 70 m showed that increasing exposure time might cause a saturation of the colors of the image, especially in the red band, that worsens the correlation between image indices and NGB. Our study suggests that the combined use of low cost devices such as UAV and a sky quality meter can be used for assessing hotspot areas of light pollution originating from the surface. Full article

Background: Whereas the efficacy and safety of intravascular lithotripsy (IVL) have been confirmed in de novo calcified coronary lesions, little is known about its utility in treating stent underexpansion. This study aimed to investigate the impact of IVL in treating stent underexpansion. Methods and Results: Consecutive patients with stent underexpansion treated with IVL entered the multicenter IVL-Dragon Registry. The procedural success (primary efficacy endpoint) was defined as a relative stent expansion >80%. Thirty days device-oriented composite endpoint (DOCE) (defined as a composite of cardiac death, target lesion revascularization, or target vessel myocardial infarction) was the secondary endpoint. A total of 62 patients were enrolled. The primary efficacy endpoint was achieved in 72.6% of patients. Both stent underexpansion 58.5% (47.5–69.7) vs. 11.4% (5.8–20.7), p < 0.001, and the stenotic area 82.6% (72.4–90.8) vs. 21.5% (11.1–37.2), p < 0.001, measured by quantitative coronary angiography improved significantly after IVL. Intravascular imaging confirmed increased stent expansion following IVL from 37.5% (16.0–66.0) to 86.0% (69.2–90.7), p < 0.001, by optical coherence tomography and from 57.0% (31.5–77.2) to 89.0% (85.0–92.0), p = 0.002, by intravascular ultrasound. Secondary endpoint occurred in one (1.6%) patient caused by cardiac death. There was no target lesion revascularization or target vessel myocardial infarction during the 30-day follow-up. Conclusions: In this real-life, largest-to-date analysis of IVL use to manage underexpanded stent, IVL proved to be an effective and safe method for facilitating stent expansion and increasing luminal gain. Full article

There is considerable attention devoted to the use of agricultural waste as a raw material substitute for commercial silica in the development of borosilicate glasses doped with rare earth oxides. Here, we present a novel structure for borosilicate glasses made from rice husk ash with a 25% molar ratio of extracted SiO₂ and doped with neodymium (GRN) or dysprosium (GRD). Adding rare earth oxides to borosilicate glasses by the melt quenching method enhanced optical transmission due to the presence of their tetrahedral geometries. GRN samples showed few bands near zero, which constitutes good utility for band rejection filters in image devices, and the samples exhibited energy values ranging from 3.03 to 3.00 eV before and after gamma irradiation. Optical transmissions of GRD samples showed peaks at 25,974, 22,172, 13,333, 11,273, 9302, 7987, and 6042 cm⁻¹. Deterioration in transmittance was observed when the investigated samples were exposed to irradiation doses of 20 and 50 kGy in the wavenumber range of 12,500 to 50,000 cm⁻¹; however, different behaviors after irradiation with 50 kGy caused an increase in transparency in comparison to 20 kGy irradiation, which was pronounced for higher wavenumbers (greater than 12,500 cm⁻¹). Photoluminescence emission and excitation spectra of the glass-doped Nd³⁺ (GRN) and glass-doped Dy³⁺ (GRD) samples were determined. GRD exhibited emission in the blue and yellow regions of the visible spectrum, which gave a white flash of light. Chromaticity coordinate (CIE) measurements of GRD samples indicated the origin of its luminous color relative to the standard white light region. Full article

The paper presents the calibration activity on the imaging system of the MINLU instrument, an autonomous sensor suite designed for monitoring light pollution using commercial off-the-shelf components. The system is extremely compact and with an overall mass below 3 kg can be easily installed as a payload for drones or sounding balloons. Drones and air balloons can in fact play an important role in completing upward light emission measurement from satellites allowing an increased spatial and time resolution from convenient altitudes and positions. The proposed system can efficiently measure the luminous intensity and the spectral power density of on-ground emissions providing a useful tool to identify polluting sources and to quantify upward light flux. The metrological performance of the imaging system has been verified through an extensive laboratory test activity using referenced light sources: the overall uncertainty of the multi-luminance meter has been calculated to be 7% of the reading, while the multi-spectrometer has shown a full width at half maximum (FWHM) equal to 10 nm within the measuring range between 400 nm and 700 nm. When operating at an altitude of 200 m, the system can achieve a horizontal resolution at a ground level of 0.12 m with a wavelength resolution able to identify the different lamp technology of outdoor light sources, including light-emitting diode (LED) lights that are undetected by satellites. Full article

High Dynamic Range (HDR) imaging using a fisheye lens has provided new opportunities to evaluate the luminous environment in visual comfort research. For glare analysis, strict calibration is necessary to extract accurate luminous maps to achieve reliable glare results. Most studies have focused on correcting the vignetting effect in HDR imaging during post-calibration. However, the lens projection also contributes to luminous map errors because of its inherent distortion. To date, there is no simple method to correct this distortion phenomenon for glare analysis. This paper presents a parametric-based methodology to correct the projection distortion from fisheye lenses for the specific use in glare analysis. HDR images were captured to examine two devices: a 190° equisolid SIGMA 8 mm F3.5 EX DG fisheye lens mounted on a Canon 5D camera, and a 195° fisheye commercial lens with an unknown projection, mounted on the rear camera of a Samsung Galaxy S7. A mathematical and geometrical model was developed to remap each pixel to correct the projection distortion using Grasshopper and MATLAB. The parametric-based method was validated using Radiance and MATLAB through checking the accuracy of pixel remapping and measuring color distortion with Structural Similarity Index (SSIM). Glare scores were used to compare the results between both devices, which validates the use of mobile phones in photometric research. The results showed that this method can be used to correct HDR images projection distortion for more accurate evaluation of the luminous environment in glare research. Full article

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. Full article

In this study, we investigated the ink formulation of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as the hole injection layer (HIL) in an organic light emitting diode (OLED) structure. Generally, in a PEDOT:PSS solution, water is incorporated in the solution for the solution process. However, the fabrication of thin film which contained the water, main solvent, could not easily form by using printing technology except spin-coating process because of the high surface tension of water. On the other hand, mixing PEDOT:PSS solution and ethanol (EtOH), a dilution solvent, could restrain the non-uniform layer that forms by the high surface tension and low volatility of water. Therefore, we printed a PEDOT:PSS solution with various concentrations of EtOH by using a nozzle printer and obtained a uniform pattern. The line width of PEDOT:PSS diluted with 90% (volume ratio) ehtanol was measured as about 4 mm with good uniformity with a 0.1 mm nozzle. Also, imaging software and a scanning electron microscope (SEM) were used to measure the uniformity of PEDOT:PSS coated on a substrate. Finally, we fabricated a green phosphorescent OLED device with printed-PEDOT:PSS with specific concentrations of EtOH and we achieved a current efficiency of 27 cd/A with uniform quality of luminance in the case of device containing 90% EtOH. Full article

The use of unmanned aerial vehicles (UAV) can allow individual tree detection for forest inventories in a cost-effective way. The scale-space filtering (SSF) algorithm is commonly used and has the capability of detecting trees of different crown sizes. In this study, we made two improvements with regard to the existing method and implementations. First, we incorporated SSF with a Lab color transformation to reduce over-detection problems associated with the original luminance image. Second, we ported four of the most time-consuming processes to the graphics processing unit (GPU) to improve computational efficiency. The proposed method was implemented using PyCUDA, which enabled access to NVIDIA’s compute unified device architecture (CUDA) through high-level scripting of the Python language. Our experiments were conducted using two images captured by the DJI Phantom 3 Professional and a most recent NVIDIA GPU GTX1080. The resulting accuracy was high, with an F-measure larger than 0.94. The speedup achieved by our parallel implementation was 44.77 and 28.54 for the first and second test image, respectively. For each 4000 × 3000 image, the total runtime was less than 1 s, which was sufficient for real-time performance and interactive application. Full article