Light Emitting Diode Illumination System Research Articles

A Tunable Hyperspectral Imager for Detection and Quantification of Marine Biofouling on Coated Surfaces

Fouling control coatings (FCCs) are used to prevent the accumulation of marine biofouling on, e.g., ship hulls, which causes increased fuel consumption and the global spread of non-indigenous species. The standards for performance evaluations of FCCs rely on visual inspections, which induce a degree of subjectivity. The use of RGB images for objective evaluations has already received interest from several authors, but the limited acquired information restricts detailed analyses class-wise. This study demonstrates that hyperspectral imaging (HSI) expands the specificity of biofouling assessments of FCCs by capturing distinguishing spectral features. We developed a staring-type hyperspectral imager using a liquid crystal tunable filter as the wavelength selective element. A novel light-emitting diode illumination system with high and uniform irradiance was designed to compensate for the low-filter transmittance. A spectral library was created from reflectance-calibrated optical signatures of representative biofouling species and coated panels. We trained a neural network on the annotated library to assign a class to each pixel. The model was evaluated on an artificially generated target, and global accuracy of 95% was estimated. The classifier was tested on coated panels (exposed at the CoaST Maritime Test Centre) with visible intergrown biofouling. The segmentation results were used to determine the coverage percentage per class. Although a detailed taxonomic description might be complex due to spectral similarities among groups, these results demonstrate the feasibility of HSI for repeatable and quantifiable biofouling detection on coated surfaces.

Experimental Design and Analysis of Adaptive LED Illumination System

Light emitting diode (LED) luminaires are widely used in street, road, and tunnel illumination. It is necessary to detect their negative effects on power grid, especially in terms of power quality distortions. In addition, because of the limited energy sources, they have to be operated in most efficient way. This paper proposed an adaptive illumination system that can be used in highway tunnels. In this context, an experimental system that consist of LED luminaires with various power values that are possible to be used in tunnel illumination was implemented. Scenarios have been created for the designed system in accordance with possible tunnel illumination scheme. Siemens S7–1200 PLC was used to control these scenarios. FFT analysis of the measurements obtained with adaptive illumination scenarios was performed and power quality distortions were determined for different harmonic levels. Similar analysis was repeated for the non-adaptive system, and a detailed comparison was proposed. In addition, both systems were compared in terms of energy consumption. Operational characteristics of adaptive illumination systems were discussed by using the obtained data. Results show that total harmonic distortion (THD) for all luminaires are active situation is quite lower than adaptive illumination scenarios, where the values of current THD are 149.7 %, 119.9 %, and 85.8 % that scenario 1, scenario 2, and all luminaires are in active situation, respectively. On the other hand, as advantage, a power saving of 73.4 % and 60.3 % can be achieved compared to different adaptive illumination scenarios according to all luminaires are active.

Sequential dark and photo fermentation hydrogen production from hydrolyzed corn stover: A pilot test using 11 m3 reactor

Pilot tests of sequential dark and photo fermentation H2 production were for the first time conducted in a 11 m3 reactor (3 m3 for dark and 8 m3 for photo compartments). A combined solar and light-emitting diode illumination system and a thermal controlling system was installed and tested. With dark fermentation unit maintained at pH 4.5 and 35 °C and photo fermentation unit at pH 7.0 and 30 °C, the overall biogas production rate using hydrolyzed corn stover as substrate reached 87.8 ± 3.8 m3/d with 68% H2 content, contributed by dark unit at 7.5 m3-H2/m3-d and by photo unit at 4.7 m3/m3-d. Large variation was noted for H2 production rate in different compartments of the tested units, revealing the adverse effects of poor mixing, washout, and other inhomogeneity associated with large reactor operations.

Study of Plant Cultivation Using a Light-Emitting Diode Illumination System to Control the Spectral Irradiance Distribution

In plant cultivation, the number of photons is more important than the light energy from the chemical reactions that occur during photosynthesis. In addition, the blue and red photon flux (B/R) ratio is an important parameter for plant cultivation. Here we discuss the effect of the spectral irradiance distribution and the B/R ratio on plant cultivation. We cultivated lettuce seedlings, Lactuca sativa L. Cv. Okayama, using a light-emitting diode illumination system that can precisely control the spectral irradiance distribution and B/R ratio. The B/R ratio varied from 0.36 to 2.06 according to the intensity of the blue light when the photosynthetic photon flux density values were sufficient to ensure the 150 - 200 μmol⋅m−2⋅s−1. High photon flux densities of blue light result in reduced plant length, plant height, and leaf area, thereby suggesting its role in the suppression of leaf growth. Therefore, we conclude that a lower photon flux of blue light (B/R Ratio) is optimal for lettuce cultivation.

Liquid-Crystal Micro-Lens Array with Square-Shaped Electrodes

We propose a liquid-crystal (LC) micro-lens array with a flat external electrode in addition to two-divided and square-shaped electrodes for electrically controlling cylindrical or spherical lens properties in each LC cell of the lens array. The LC micro-lens array is useful for tuning optical properties such a focal length and deflection angle of a light emitting diode illumination system.

High-brightness, high-power LED-based strobe illumination for double-frame micro particle image velocimetry

There is a need for more practical, cost-effective and adaptive flow measurement instruments. Unfortunately, most of the current equipment still has to employ bulky and expensive laser systems for flow illumination. In this work we explore the practicability of using high-brightness high-power light-emitting diodes (LED) as a strobe-light illuminator within a double-frame micro particle image velocimetry (microPIV) system. A compact, cost-effective, and controllable LED driver was designed and applied to study the optical and spectral behavior of green and blue family direct-color single chip LEDs, which have excitation wavelengths corresponding to the most widely used fluorescent micro particles. To achieve strobe illumination, LEDs were subjected to high current double-pulsed operating regimes (up to 35A at 20μs pulse duration), which are much beyond their physical damage thresholds. We have witnessed that the blue family LEDs are more suitable for the fluorescence based microPIV experiments as they exhibit more stable spectral behavior at the double-pulsed high currents compared to the green colored LEDs. Specifically, we have observed that the spectral wavelength shift of blue family LEDs due to the high current is less severe and still enough to excite particles than that of green LEDs. Also, we have studied the relation between the pulse duration (as a means of parameter controlling signal-to-noise ratio) and the motion blur effect that arises due to the prolonged pulse durations. As a result, adequate pulse durations for most widely used microPIV experimental conditions were calculated. The feasibility and robustness of the developed double-pulsed LED illumination system was validated through a series of microPIV experiments with real flows inside two different topology microchannels, where the measured velocity was in good agreement with the corresponding analytical solutions. Overall, we can conclude that the high-brightness LED devices are promising candidates to replace their laser counterparts in the microPIV systems.

Improving the uniformity of luminous system in radial imaging capsule endoscope system

This study concerns the illumination system in a radial imaging capsule endoscope (RICE). Uniformly illuminating the object is difficult because the intensity of the light from the light emitting diodes (LEDs) varies with angular displacement. When light is emitted from the surface of the LED, it first encounters the cone mirror, from which it is reflected, before directly passing through the lenses and complementary metal oxide semiconductor (CMOS) sensor. The light that is strongly reflected from the transparent view window (TVW) propagates again to the cone mirror, to be reflected and to pass through the lenses and CMOS sensor. The above two phenomena cause overblooming on the image plane. Overblooming causes nonuniform illumination on the image plane and consequently reduced image quality. In this work, optical design software was utilized to construct a photometric model for the optimal design of the LED illumination system. Based on the original RICE model, this paper proposes an optimal design to improve the uniformity of the illumination. The illumination uniformity in the RICE is increased from its original value of 0.128 to 0.69, greatly improving light uniformity.

Nonspherical LED packaging lens for uniformity improvement

Light emitting diode (LED) has more advantages compared with a traditional incandescent light bulb and a fluorescent lamp, such as small size, low quantity of heat, long life, low power consumption, fast response, plain packaging and ease of develop ment of a frivolous short product. A methodology is proposed to improve the uniformity of the LED illumination system. As a light source in a backlight unit (BLU), the requirement for optical characteristics of a LED is different from highly directional conventional ones. New diffused-type LEDs need to be developed to fulfill the requirement of the BLU industry. A non-spherical lens is designed to optimize uniformity, and a great improvement in uniformity from 28.4 to 64% is demonstrated. In the future, it may used in an LED display to improve the unevenness of illumination.

Guiding Light From LED Array Via Tapered Light Pipe for Illumination Systems Design

In illumination systems, it is often necessary to get a structure that can have good performance on uniformity. Although light-emitting diodes (LEDs) are replacing conventional light sources in illumination systems, they have nonuniformity and a large view angle. In this paper, an LED illumination system has been designed that can use color sequential to replace the color wheel for projector and also can mix color to get the color you want. An optical element tapered light pipe is also used in this structure, and we investigate the mechanism of irradiance distribution. It assists in the design of light pipe for different applications. The efficiency is above 80% and the uniformity is better than 60%. The formation of irradiance distribution in the tapered light pipe is discussed, both analytically and numerically. The result of the simulation verifies that efficiency of this structure is well enough for the illumination of both car headlights and interior lighting. This illumination system also provides a good color-mixing effect that can replace arc lamps or fluorescent lamps.

Designing Uniform Illumination Systems by Surface-Tailored Lens and Configurations of LED Arrays

Light-emitting diodes (LEDs) are gradually becoming the preferred choice for many lighting applications that require uniform illumination distribution. LED sources are usually composed of several individual LEDs which must be mounted on a panel as a lighting module. Therefore, the design is quite important for achieving a good uniform illumination distribution before a LED lighting module is produced. This paper presents a theory and design method by systemic concepts and focuses on the study of optical properties. We can design, efficiently, a LED lighting module and achieve a satisfactory uniformity by this theory and method, the design of a uniform LED illumination system. By this method, we not only obtain the maximally flat illumination distribution but also the emitting angle of the system can be designed at will. This method and theory will offer a preferable choice when LED lighting modules become the main stream for the lighting market in the future. Here, the light source is approximately defined as a point light source with cosine irradiance distribution.