LED Spectrum Research Articles

Luminous and Melanopic Efficiency Performance of Phosphor-Converted LEDs with Tunable Spectral Characteristics

In this work, we investigated the luminous and melanopic efficiency of the radiation (LER/MER) performances of phosphor-converted LEDs (PC LEDs) with tunable spectral characteristics, namely peak wavelength, full width at half maximum (FWHM), and emission intensity. We constructed theoretical PC LED spectra based on the characteristics extracted from the database of IES TM-30-15, analyzed the relations between LER/MER and different spectral characteristics, and proposed spectral composition strategies at various correlated color temperatures (CCTs). Results showed that both MER and LER are linear with the FWHM of phosphor within the peak wavelength range in practical use, but the change in values by tuning emission intensity varies with spectral compositions. Hence, different spectral characteristics should be considered comprehensively. We further explored the trade-off between luminous and melanopic efficiency. Lowering the FWHM of phosphor and the intensity distribution of the blue LED can obtain higher LER and low circadian effect at lower CCT. As CCT increases, considering color rendering and the increase in the blue intensity distribution, besides reducing FWHM, tuning the peak wavelength close to the peak wavelength of V(λ) helps to reduce the circadian effect. These investigations provide optimization strategies for ideal melanopic and luminous performance of PC LED light sources.

LED Zappelin’: An open source LED controller for arbitrary spectrum visual stimulation and optogenetics during 2-photon imaging

Two-photon (2P) microscopy is a cornerstone technique in neuroscience research. However, combining 2P imaging with spectrally arbitrary light stimulation can be challenging due to crosstalk between stimulation light and fluorescence detection. To overcome this limitation, we present a simple and low-cost electronic solution based on an ESP32 microcontroller and a TLC5947 LED driver to rapidly time-interleave stimulation and detection epochs during scans. Implemented for less than $100, our design can independently drive up to 24 arbitrary spectrum LEDs to meet user requirements. We demonstrate the utility of our stimulator for colour vision experiments on the in vivo tetrachromatic zebrafish retina and for optogenetic circuit mapping in Drosophila.

Effects of LED spectra on growth, gas exchange, antioxidant activity and nutritional quality of vegetable species

This research aimed to investigate the effects of three LED spectra on growth, gas exchange, antioxidant activity and nutritional quality of three vegetable species. The compressible vegetable facilities (CVF) were developed and three kinds of typical LED lights (spectra) were set, including white LED light (W), red-blue-green LED light (RBG), and red-blue-white LED light (RBW). Three vegetable species, i.e. lettuce (Lactuca sativa L. cv. Rome), cherry radish (Raphanus sativas L. cv. Hongxin) and cherry tomato (Lycopersicon esculentum M. cv. Mosite), were chosen and grown (matrix culture) in the three LED lights for 40, 40 and 100 days, respectively. The results indicated that the vegetable plants grew well and were compact in the RBG and RBW treatments. There was the highest biomass or fruit (tomato) in the RBG treatment and the least one in the W treatment for three vegetable species. There were no significant differences in harvest index, ratio of shoot to root, and water content among three treatments. The production efficiency values of 9.0-9.7, 9.9-13.5 and 11.8-12.5 g DW d−1 m−2 for lettuce, radish and tomato plants in the RBG and the RBW treatments were higher than those in the W treatment. The photosynthetic and transpiration rates of three vegetable species in the RBG treatment were the highest among three treatments and the W treatment had the least one. There were significant effects of three spectra on antioxidant activities of three vegetable species. Higher PPFD percentages of blue in the RBG light and the RBW light increased the antioxidant activities of all vegetable plants compared the W light. But it had no significant difference between the RBG light and the RBW. The organic components including soluble sugar (SS) and protein (Prt) of lettuce and radish plants were affected significantly by three spectra, but not for tomato plants. The contents of Mg and Zn of radish plants in the RBG treatment were higher than those in other treatments. There were significant positive effects of RBW treatment on the contents of N and Mg of tomato plants. The different spectra did not affect the contents of N-NO3 and Cu of vegetable plants. This study demonstrated that the RBG light (spectrum) significantly enhanced the growth, gas exchange, antioxidant activity of the lettuce, radish, and tomato cultivars used in this study, and there are significant effects of different LED spectra on the nutritional quality (including organic components and several mineral elements) of the different species.

Spectral Optimization of White LED Based on Mesopic Luminance and Color Gamut Volume for Dim Lighting Conditions

The study aims to propose an approach of white LED spectral optimization based on mesopic luminance and color gamut volume for dim lighting conditions. Three optimal white LED spectra with relatively higher mesopic luminance and color gamut volume, the highest mesopic luminance, and the largest gamut volume are recommended for reducing energy consumption and enhancing color perception and recognition of human eyes. The theoretical simulation shows that the spectra with higher correlated color temperatures (CCT) and S/P-ratio increase the mesopic luminance and also extend the range of color gamut with the decreasing of lighting level. An evaluation model is developed to faster predict mesopic luminance, color gamut volume, and S/P ratio for lighting applications.

Avalanche leds based on nanostructured silicon for optical interconnections

The paper analyzes the parameters of silicon avalanche LEDs and their use for electron-optical signal transmission systems. The advantages of silicon avalanche LEDs are shown, among which high speed and compatibility with silicon technology should be highlighted. Experimental avalanche LEDs based on nanostructured silicon were fabricated and studied. The results of controlling the electroluminescence spectrum of avalanche LEDs due to the choice of production conditions to form nanostructured silicon are presented. It was found that the temperature of the substrate during the deposition of the surface nanocomposite aluminum + silicon film affected the size of the formed silicon nanoparticles determining the spectral characteristics of avalanche LEDs. This allows shifting the maximum of their emission spectrum to a shorter wavelength region of the visible range due to the forming of smaller silicon nanoparticles. The authors have developed an optical interconnection system consisting of avalanche LEDs based on nanostructured silicon and a microchannel silicon wafer used to transmit a light signal. The study of various operating modes of the developed optoelectronic system was performed and an increase in the efficiency of optocouple based on avalanche LEDs to 0.2% due to the pulsed operating mode was achieved. It is shown that the efficiency of the optocouple increases with LED current and it is the pulsed mode of its operation that is characterized by the maximum current, which is due to more efficient removal of Joule heat in the intervals between pulses, ensuring stable operation of the entire system. The results obtained open up new opportunities for the development of optical interconnections between silicon chips and silicon optoelectronics in general.

Studies of the Effect of Combined Spectrum LED Phytoradiators on the Growth and Development of Cucumber Plants

The article presents the results of photobiological studies aimed at determining the preferred requirements for the spectrum of combined spectrum LED phytoradiators for the light culture of cucumber plants, variety Liliput F1. The studies were conducted in the artificial climate laboratory of FSBEI HE N.P. Ogarev Moscow State University, using an experimental research hydroponic plant. The results are presented and the effect of the spectral compositions of phytoradiators based on LEDs on the growth and development of Liliput F1 cucumber plants is estimated. The studies (the first vegetation) made it possible to preliminarily identify the most favorable radiation spectrum, which provides the best biometric characteristics and productivity of plants of Liliput F1 cucumbers.

Realization of a Laboratory Tuneable Colour Light Source

A spectrally tuneable colour light source (TCLS) has been designed and constructed at Physikalisch-Technische Bundesanstalt (PTB), Germany. It consists of an integrating sphere with 24 LEDs which are driven by a computer-controlled power supply. It is intended for producing any visible spectral distribution and to mimic various light sources for use in laboratories as a calibration source. With the help of an integrated spectrometer, a closed loop operation was introduced to improve the performance of the TCLS and to spectrally stabilize its output spectrum. Before practical realization of the TCLS a series of simulations have been made to predict its performance and capability with a number of different target spectrums. During the practical implementation we have encountered difficulties, namely optimization of the output spectrum, dependency of LED spectra on the electric current through the LED and temperature of the LED, non-linearity of LED’s luminous flux with respect to electric current through the LED and some difficulties with small synthesis coefficient values, which were all successfully solved.

Response of photosynthate distribution in potato plants to different LED spectra.

Although light is essential to photosynthesis, few studies have examined the effects of different LED spectra on photosynthate distribution in potato plants. Therefore, we exposed tuberising potato plants to white (W), red (R), blue (B) and green (G) LED treatments and compared tuber development and carbohydrate partitioning among the plants. R-treated plants had greater photosynthetic leaf area during tuber development compared with those under other treatments, thus enhancing assimilation. Although R-treated plants had higher 13C assimilation in the leaves, stems and roots than those under B treatment, there was no difference in partitioning of 13C assimilation and yield in the tubers of each plant between R and B treatments. For the tuber size, R-treated plants had a higher ratio of large tubers (>20 g) and a lower ratio of small (2-20 g) and medium-sized (10-20 g) tubers than those under W. B-treated plants had more medium-sized and large tubers than those under W. The reason may be that plants under R treatment distributed more assimilated 13C in their first tuber than those under other treatments. By contrast, plants under B balanced photosynthate distribution among their tubers. Leaves under G treatment had lower photosynthetic efficiency and ΦPSII than those under W, R or B treatment, which resulted in lower 13C photosynthate allocation in organs and lower tuber yield per plant than in R and B treatments. Overall, R treatment promoted 13C assimilation and led to more large tubers than other treatments. B-treated plants distributed more photosynthates into tubers rather than other organs and showed balanced tuber development.

시뮬레이션을 통한 455nm 청색 LED 여기 광원과 형광체 조합에 따른 연색특성 변화 연구

Recently, studies have been performed regarding to various methods of improving color rendering properties of white LEDs by mixing warm white (WW) and cool white (CW) or red (R), green (G), blue (B), and yellow (Y) LED spectra. However, the previous researches have been insufficient in presenting maximum optical characteristics over all correlated color temperature (CCT) ranges or representing recently suggested evaluation methods of color rendering properties. In this paper, color rendering properties including the recent methods at all CCTs will be investigated through simulation combining various kinds of phosphors excited by a 455nm blue LED. For evaluating CRI values, general and special color rendering indices (RSUBa/SUB and RSUB9∼14/SUB), general color quality scale (QSUBa/SUB), fidelity index (RSUBf/SUB), and color gamut (RSUBg/SUB) will be examined and compared by root mean square (RMS) values. 2-phosphor combination with a blue LED resulted in RSUBa/SUB≥95, RSUB1∼14/SUB≥75, and QSUBa/SUB≥90, 3-phosphor in RSUBa/SUB≥98, RSUB1∼14/SUB≥75, and QSUBa/SUB≥97, and 4-phosphor in RSUBa/SUB≥94, RSUB1∼14/SUB≥71, and QSUBa/SUB≥90.

455nm LED 파장과 형광체 조합에 따른 S/P Ratio 변화에 대한 전산모사 연구

455nm LED 파장과 형광체 조합에 따른 S/P Ratio 변화에 대한 전산모사 연구

Screening of microalgae and LED grow light spectra for effective removal of dissolved nutrients from cold-water recirculating aquaculture system (RAS) wastewater

Popularity of recirculating aquaculture systems (RAS) is increasing. Because of the high water recirculation rate, dissolved nutrients originating from fish feed are concentrated enough in RAS wastewater (WW) to enable growth of primary producers, e.g. microalgae. This study evaluated nitrate-nitrogen (NO3-N) and phosphate-phosphorus (PO4-P) removal efficiency of ten temperate zone freshwater microalgae species during their exponential growth phase in unfiltered RAS WW at 17 ± 0.5 °C. Growth and nutrient uptake efficiency of six green and four non-green microalgae strains were compared between WW and reference growth medium in batch monocultures. The effect of three different LED grow light spectra on growth and nutrient uptake efficiency were compared for four green microalgae in WW. The specific growth rate (SGR, 0.5-0.8 d−1) and removal of NO3-N (N%, 57–96%) and PO4-P (P%, 78–94%) of green microalgae in WW in 4 days were comparable to the results obtained in the reference medium (SGR, 0.6-0.9 d−1, N%, 59–99%; P%, 86–99%). In contrast, non-green microalgae had negligible growth (SGR, from -0.1 to 0.2 d−1) and poor nutrient removal (N%, 1–29%; P%, 0–34%) in both growth media after 9 days. The three LED spectra did not differ on their effect on growth and nutrient removal of three green microalgae in WW after 4 days, while the fourth tested species, Haematoccocus pluvialis, had its highest nutrient removal after 8 days under a specific LED spectrum. Current results show that RAS WW supports well green microalgae growth in batch cultures in temperatures common in Nordic RAS and that continuous spectrum LED grow lights can induce high removal of dissolved nutrients. Our findings lend support to the concept of using temperate zone microalgae for nutrient removal and recycling from RAS WW.

Hardware-Software Complex for the Investigation of the Dynamic Characteristics of Separate Spectral Components of the Emission Spectrum of Leds

We present the description of an automated hardware-software complex intended for measuring the 3 dB frequency of modulation and evaluation of the quantum efficiency of separate spectral components of the full spectrum of electroluminescence of light-emitting diodes, including the range of low levels of excitation. The principle of operation of this complex is based on measuring the spectrum of radiation of a light-emitting diode with the help of an OceanOptics USB2000+ spectrometer in the signal-accumulation mode in the course of transmission of current pulses with given amplitude and repetition frequency through the light-emitting diode with subsequent selection of separate spectral components from the full spectrum of radiation. We present the results of testing the hardware-software complex performed by measuring, as an example, the frequency characteristics of separate spectral components of the full electroluminescence spectrum of commercial InGaN green light-emitting diodes. The analyzed hardware-software complex can be used for the diagnostics of the quality of light-emitting heterostructures with quantum wells.

Bayesian-based spectral deconvolution with genetic algorithm

Spectral distortions exist widely due to the broadening effects of spectrometer. In this paper, a spectral deconvolution method using genetic algorithm is proposed to solve this problem. In the Bayesian framework, the spectral deconvolution model is constructed with Gaussian noise and Poisson noise hypothesis, and the prior term is constructed with adaptive Gauss-Markov priori. Genetic algorithm is employed to optimize the spectral deconvolution model to obtain the corrected spectrum. To verify the effectiveness of the proposed method, simulated degraded LED spectra with different colour temperature are corrected by the proposed method, Richardson-Lucy method and Levenberg-Marquardt method. Experimental results show that the proposed method can correct the spectra effectively.

Red Sea corals under Artificial Light Pollution at Night (ALAN) undergo oxidative stress and photosynthetic impairment.

Coral reefs represent the most diverse marine ecosystem on the planet, yet they are undergoing an unprecedented decline due to a combination of increasing global and local stressors. Despite the wealth of research investigating these stressors, Artificial Light Pollution at Night (ALAN) or “ecological light pollution” represents an emerging threat that has received little attention in the context of coral reefs, despite the potential of disrupting the chronobiology, physiology, behavior, and other biological processes of coral reef organisms. Scleractinian corals, the framework builders of coral reefs, depend on lunar illumination cues to synchronize their biological rhythms such as behavior, reproduction and physiology. While, light pollution (POL) may mask and lead de‐synchronization of these biological rhythms process. To reveal if ALAN impacts coral physiology, we have studied two coral species, Acropora eurystoma and Pocillopora damicornis, from the Gulf of Eilat/Aqaba, Red Sea, which is undergoing urban development that has led to severe POL at night. Our two experimental design data revealed that corals exposed to ALAN face an oxidative stress condition, show lower photosynthesis performances measured by electron transport rate (ETR), as well as changes in chlorophyll and algae density parameters. Testing different lights such as Blue LED and White LED spectrum showed more extreme impact in comparison to Yellow LEDs on coral physiology. The finding of this work sheds light on the emerging threat of POL and the impacts on the biology and ecology of Scleractinian corals, and will help to formulate specific management implementations to mitigate its potentially harmful impacts.

Features of measuring the brightness of the screens

The situation with the metrological assurance of brightness measurements in Ukraine is analyzed. The main regulatory documents for the characterization of lux meters are considered. It was noted, that the components of the uncertainty of brightness due to the difference in the spectral composition of radiation, during calibration and measurement, as well as uncertainties due to spatial heterogeneity of the screens, are not fully considered. The characteristic values of these uncertainties are calculated by the method of mathematical modeling, using generally accepted calculation methods. To calculate the spectral errors, the literature data on the spectra of CCFL and LED monitors were used, as well as the modeling of the spectra of blue, green and red radiation sources, using Gaussian distribution with varying widths. It is shown, that for а brightness meter calibrated by а type A source, the use of white screens for measuring the brightness will result in errors, less than 7%. It is shown, that when calibrating the brightness meter using the CCFL screen and then using the LED for the screen, the errors will be about 1%. Simple formulas are given to evaluate the effect of screen heterogeneity. For а refined assessment of the influence of spatial inhomogeneity, mathematical modeling was carried out — 3 types of brightness distribution, were used with decreasing radiation distribution density and two types of viewing area — а circle (imitation of brightness measurement, using а diaphragm) and а Gaussian distribution (imitation of brightness measurement with а lens) equal widths. It is shown, that for the field of sight in the form of а Gaussian distribution, the influence of the inhomogeneity of the distribution of screen illumination, when moving and changing the width of the field of sight is insignificant. Two approaches have been proposed for building the material base for metrological assurance of brightness measurements.

Comparison of MAP method with classical methods for bandpass correction of white LED spectra.

The bandwidth of a spectrometer is an important error-influencing factor in spectral measurement. To obtain accurate results, bandpass correction is an indispensable step in spectral data processing. To deal with such a problem, several methods have been proposed, including the differential operator method using a local polynomial approximation and the Richardson-Lucy method combined with a regularization. Here we employ a method based on the maximum a posteriori estimation. The efficiency of the method is verified through a large number of experiments on the spectra of white light-emitting diodes. By comparing the error of the reference spectrum, it was found that this method can effectively correct spectra, thus providing more accurate information for further analysis.

Bandwidth correction of spectral measurement based on Levenberg-Marquardt algorithm with improved Tikhonov regularization.

Spectroscopic data often suffers from spectral distortions due to the broadening effects of the spectrometer. In this paper, the issue of bandwidth correction is transformed into a multiparameter optimization problem, and an improved bandwidth correction method based on the Levenberg-Marquardt algorithm with improved Tikhonov regularization is presented. Example LED, Raman, and compact fluorescent lamp spectra were corrected with the proposed method, the Richardson-Lucy method, and the maximum a posterior method, and the correction errors and runtimes under the same stopping conditions of each method were compared. The experimental results show that the proposed method can be applied to different spectra with excellent correction.

Light quality and intensity of light-emitting diodes during pre-cultivation of Picea abies (L.) Karst. and Pinus sylvestris L. seedlings – impact on growth performance, seedling quality and energy consumption

ABSTRACTThree different LED lamps with continuous spectra were compared against commonly used fluorescent lights. The lamps were characterized by light output, energy consumption and spectral quality for plant growth. The biological effects of light quality were compared by pre-cultivating seedlings of Picea abies (L.) Karst. and Pinus sylvestris L. under each spectrum for 35 days in a growth chamber with controlled temperature, humidity and photoperiod. The seedlings were then transplanted and cultivated for one vegetation period at the nursery, then planted outdoors on a forest field trial and followed for three years. The seedlings showed similar growth performance for all spectra tested. LED lamps have several advantages to fluorescent light such as energy consumption, longer life span and adjustable light intensity. Regarding light intensity the effects on growth performance were studied for both species using the most promising LED spectra. The photosynthetically active radiation (PAR) was maintained at 50, 100, 200 and 400 μmol m−2 s−1. Unlike energy consumption, seedling development did not display a linear relationship to light intensity. Instead, the results show an optimum light level between 100 and 200 μmol m−2 s−1 for the shade tolerant Picea abies seedlings and a level of around 200 μmol m−2 s−1 for the more shade intolerant Pinus sylvestris seedlings.

CCT 조절형 백색 LED와 단일 파장 LED의 스펙트럼 조합에 따른 S/P Ratio와 CRI 변화에 대한 전산모사 연구

CCT 조절형 백색 LED와 단일 파장 LED의 스펙트럼 조합에 따른 S/P Ratio와 CRI 변화에 대한 전산모사 연구

NO<sub>2</sub> measurement using fiber coupled broadband LED source combining a Herriott multi-pass cell

An NO<sub>2</sub> sensor based on a fiber coupled broadband LED source with a Herriott multi-pass cell is developed and demonstrated for calibrating aerosol absorption photoacoustic (PA) spectrometer. At first, a Herriott multi-pass cell with an effective optical path of 26.1 m is designed based on the theory of light transmission, for increasing the light absorption of NO<sub>2</sub> in the cell. It is difficult to obtain a high-quality beam of LED by using the conventional collimating method that enables the collimated output beam to transmit back and forth in the multi-pass cell, due to the large emitting surface and divergence angle of the LED. So, in the present work, the emission of the LED is coupled into a single model fiber, and then collimated by using a lens. The LED spectrum does not change before and after fiber coupling. The collimated beam with a central wavelength of 438.5 nm is coupled into the multi-pass cell. The output beam passing through the multi-pass cell is detected by using a spectrometer for retrieving the NO<sub>2</sub> concentration. Finally, an expected concentration detection limit of 1 μmol/mol (3<i>σ</i>) is achieved within 1 s acquisition time and the signal-to-noise ratio (SNR) is 40. By analyzing the result measured with 46 μmol/mol NO<sub>2</sub>, a measurement precision of 0.1% is achieved. In order to calibrate the aerosol absorption PA spectrometer, the NO<sub>2</sub> sensor and the aerosol absorption PA spectrometer based on 450 nm are used to measure different concentrations of NO<sub>2</sub>, simultaneously. The results show that the measured NO<sub>2</sub> concentration has a good linear relationship with the PA spectrum signal, and the linearity is better than 99.9%. This good linear relationship further shows the feasibility and reliability of the NO<sub>2</sub> sensor. The slope of calibration curve after normalizing the power is 0.95 nV/(mW·Mm<sup>-1</sup>). Using this calibration result, the PA signal measured with aerosol absorption PA spectrometer is transformed into the absorption coefficient. The developed NO<sub>2</sub> measuring system based on a broadband LED light source and Herriott multi-pass cell has the advantages of low cost, simple structure and easy use. It can be used to calibrate the aerosol absorption PA spectrometer, and also to measure NO<sub>2</sub> in industry.