Light-emitting diodes (LEDs) play a major role in many applications where intense light irradiati... more Light-emitting diodes (LEDs) play a major role in many applications where intense light irradiation is necessary. There are several LED radiation pattern models, which are widely used, but are valid only for far-field. In this work, we propose a mathematical model for the spatial distribution of irradiance of LEDs at near working distances.
Ray tracing in a metasurface is the process to obtain the three-dimensional (3D) light path under... more Ray tracing in a metasurface is the process to obtain the three-dimensional (3D) light path under reflection and transmission, which may be helpful in the optical design of metalenses and other metaoptical devices. In this work, first we deduce the 3D vector form of Snell's law for metasurfaces by using a geometric approach. And then, we deduce the general equations to calculate the direction of the reflected and refracted beams in any metasurface, and for any incident beam. In other words, we derive vector form equations for the 3D direction of transmitted and reflected beams at a metasurface with arbitrary 2D phase profile, and for any 3D direction of incident light.
Ray tracing in a metasurface is the process to obtain the three-dimensional (3D) light path under... more Ray tracing in a metasurface is the process to obtain the three-dimensional (3D) light path under reflection and transmission, which may be helpful in the optical design of metalenses and other metaoptical devices. In this work, first we deduce the 3D vector form of Snell's law for metasurfaces by using a geometric approach. And then, we deduce the general equations to calculate the direction of the reflected and refracted beams in any metasurface, and for any incident beam. In other words, we derive vector form equations for the 3D direction of transmitted and reflected beams at a metasurface with arbitrary 2D phase profile, and for any 3D direction of incident light.
Aggregates of superparamagnetic colloids confined in liposomes in the presence of a controllable ... more Aggregates of superparamagnetic colloids confined in liposomes in the presence of a controllable external magnetic field are studied here by computer simulation. A model of a hard sphere with a central dipole has been used to simulate secondary particles of colloids confined to move within a liposome, which is modelled as a hard spherical cavity. We focus our study on the structure of aggregates created by secondary particles, which in turn are formed by superparamagnetic particles. This study was performed by using the conventional Monte Carlo simulations and the cluster-moving Monte Carlo method. The results obtained with both methods show a dependence on the number of particles and on the ratio cavity-colloid diameters. However, the usual Monte Carlo method does not allow the collective movement of the aggregates. The simulation results show, that for the particular case of the liposome diameter obtained from the experiments , the formation of a single ribbons located at the centre of the cavity for N = 30 and N = 60. In addition, we analyse the structure formation for different values of , the equilibrium structures are chains for systems for lower , whereas ribbons formation are structures of equilibrium for . GRAPHICAL ABSTRACT
In this work, we deduce an exact analytical solution of irradiance produced by a Lambertian recta... more In this work, we deduce an exact analytical solution of irradiance produced by a Lambertian rectangular source at short distances, which may approximate the irradiance of a typical light-emitting diode (LED) with rectangular shape.
Many emerging light-emitting diode (LED) applications require short-distance illumination. For th... more Many emerging light-emitting diode (LED) applications require short-distance illumination. For that, we derive an exact formula of the illumination profile produced by Lambertian LEDs, in which all parameters are fundamental constants. Moreover, we propose a general, simple, but accurate mathematical model of the irradiance pattern, valid for Lambertian and non-Lambertian LEDs at short distances. This model provides the irradiance profile as a function of both the LED-target distance and the coordinates of every point on the irradiated surface. The model is formulated in terms of simple sigmoid functions, in which LED size and light flux are fundamental parameters. The accuracy of the irradiance pattern model is tested both with theory and with experimental measurements.
We describe the differential cell design and the experimental (optical and electronic) setup for ... more We describe the differential cell design and the experimental (optical and electronic) setup for the differential front photopyroelectric technique, whose theory has been developed in the first part of this paper (Ivanov et al 2008 J. Phys. D: Appl. Phys. 41 085106). We will show first how the direct (non-differential) front photopyroelectric theory described in our previous paper reproduces well the experimental results. The usefulness of the differential technique is demonstrated by means of experimental measurements of the thermal effusivity in binary ethanol-water and glycerol-water mixtures, based on a theoretical methodology that simplifies the measurement procedure and diminishes the experimental uncertainty.
Ceramic phosphor plates of cerium (Ce 3+) doped oxyfluoride were fabricated by the solid state re... more Ceramic phosphor plates of cerium (Ce 3+) doped oxyfluoride were fabricated by the solid state reaction method. These phosphors exhibit efficient emission, with the novel feature of color tuning by varying both the doping concentration and excitation wavelength. As the Ce 3+ concentration increases, the excitation spectrum broadens by a factor of 1.6, and the excitation peak wavelength shifts from 390 nm to 435 nm, and there is a variation in excitation energy of ~ 10%. Luminescence spectrum of low Ce 3+ concentration samples is tuned from blue to green with the change of excitation wavelength. The emission peak exhibits a shift of 58 nm into the red spectral region, varying the Ce 3+ concentration from 0.05 to 0.1 mol%; while this shift is only 6 nm when Ce 3+ content changes from 0.25 to 1 mol%. Photoluminescence (PL) quantum yield has achieved 76%. The crystal structure was examined using X-ray diffraction to explain its possible influence on the redshift luminescence. A proof of concept of white LED was constructed using a 450 nm blue LED chip with an oxyfluoride phosphor plate, showing a luminous efficacy (LE) of 64 lm/W with a color rendering index of 74.
Latin America Optics and Photonics Conference, 2016
Strong emission of green light in ceramic glass was obtained. The intensity of the emitted signal... more Strong emission of green light in ceramic glass was obtained. The intensity of the emitted signal changes with the heat treatment temperature.
Latin America Optics and Photonics Conference, 2016
Strong green-yellow emission in Eu2+ doped glass ceramic as a function of rare earth concentratio... more Strong green-yellow emission in Eu2+ doped glass ceramic as a function of rare earth concentration was obtained. Proof of concept for solid state white lighting with high power AC LED was fabricated.
Convolutional neural networks (CNNs) and digital holographic interferometry (DHI) can be combined... more Convolutional neural networks (CNNs) and digital holographic interferometry (DHI) can be combined to improve the calculation efficiency and to simplify the procedures of many DHI applications. In DHI, for the measurements of concentration differences between liquid samples, two or more holograms are compared to find the difference phases among them, and then to estimate the concentration values. However, liquid samples with high concentration difference values are difficult to calculate using common phase unwrapping methods as they have high spatial frequencies. In this research, a new method to skip the phase unwrapping process in DHI, based on CNNs, is proposed. For this, images acquired by Guerrero-Mendez et al. (Metrology and Measurement Systems 24, 19–26, 2017) were used to train the CNN, and a multiple linear regression algorithm was fitted to estimate the concentration values for liquid samples. In addition, new images were recorded to evaluate the performance of the proposed...
A multichip light-emitting diode (LED) should not be treated as a point source at short-distance ... more A multichip light-emitting diode (LED) should not be treated as a point source at short-distance illumination. For that, we propose a general, simple, but accurate mathematical model of the irradiance spatial distribution for multichip LEDs, valid at very short distance illumination. This model provides the irradiance profile as a function of both the LED-target distance and the coordinates of every point on the irradiated surface. The model is formulated in function of the chip array geometry, number chips, multichip LED size, and light flux. The accuracy of the irradiance pattern model is tested both with theory and with experimental measurements.
Resumen es: Al planear un experimento con la tecnica fotopiroelectrica, se deben encontrar los pa... more Resumen es: Al planear un experimento con la tecnica fotopiroelectrica, se deben encontrar los parametros adecuados del equipo de medicion para evitar la distorsion ...
We have implemented an exact ray trace through a plano-freeform surface for an incident plane wav... more We have implemented an exact ray trace through a plano-freeform surface for an incident plane wavefront. We obtain two caustic surfaces and provide the critical points related to the ray tracing process. Additionally, we study the propagation of the refracted wavefronts through the plane-curved surface. Finally, by using the Ronchi-Hartmann type null screen and placing the detection plane within the caustic region, we have evaluated the shape of a plano-freeform optical surface under test, obtaining an RMS difference in sagitta value of 6.3 μm.
Light stimulation and biofloc technology can be combined to improve the efficiency and sustainabi... more Light stimulation and biofloc technology can be combined to improve the efficiency and sustainability of tilapia production. A 73-day pilot experiment was conducted to investigate the effect of colored light on growth rates and nutritional composition of the Nile tilapia fingerlings (Oreochromis niloticus) in biofloc systems. The effect of colored light on the nutritional composition of bioflocs as a food source for fish was measured. Three groups were illuminated in addition to natural sunlight with colored light using RGB light emitting diodes (LEDs) with peak wavelengths (λ) of 627.27 nm for red (R), 513.33 nm for green (G), and 451.67 nm for blue (B) light. LED light intensity was constant (0.832 mW/cm 2), and had an 18-h photoperiod of light per day throughout the study. The control group was illuminated only with natural sunlight (natural). Tilapia had an average initial weight of 0.242 g. There was a significant effect of colored light on tilapia growth and composition. The R group showed the best growth rate, highest survival, and highest lipid content. The B group showed homogeneous growth with the lowest growth rate and lipid content, but the highest protein level. On the other hand, the biofloc composition was influenced by the green light in the highest content of lipids, protein, and nitrogen-free extract.
Street lighting, which is one of the main players in energy waste and light pollution at night, s... more Street lighting, which is one of the main players in energy waste and light pollution at night, still faces the challenge of efficient lighting of roadways with curved and twisted shapes. To meet this challenge, we propose an effective and efficient adaptive lightemitting diode (LED) luminaire. This LED lamp delivers a roadway-shape light pattern, which maximizes illumination performance. The light is efficiently and homogeneously directed only where is needed; which reduces glare, and improves both the eye comfort and the visual discrimination ability of car drivers and pedestrians. The proposed luminaire is very practical in that it only requires to replace the cover plate, which is a special microlens array sheet, to produce different shape light patterns. The adaptive mechanism is simple and effective: LED light is first collimated and then efficiently distributed on a freeform roadway by the special microlens sheet. We present an extensive analysis of the lighting adaptability of the proposed luminaire by Monte Carlo ray tracing. In particular, we studied the effect of the main microlens structural parameters in the shape and size of the delivered illumination distribution on the roadway. We present a design example, a prototype construction, and an experimental confirmation on a scale street lighting system. Simulations and experimental results show the advantages of adaptive luminaires over the traditional nonadaptive approaches.
Current Developments in Lens Design and Optical Engineering XIX
To date, many studies on the optimization of the spectral power distributions (SPDs) have been co... more To date, many studies on the optimization of the spectral power distributions (SPDs) have been conducted to maximize the energy performance and color quality of white light-emitting diodes (LEDs). Here, not only for LEDs but for any light source, we numerically calculate the SPDs which maximize luminous efficacy of radiation (LER) in function of the color rendering index and of color temperature. As previously reported in the literature, we obtain optimal SPDs that are discrete spectra rather than continuous, but with considerably higher LER values. Such optimal SPDs may be used to design various lighting technologies: incandescent, fluorescent, high-intensity discharge, laser, and solid-state lighting.
A method for modeling the irradiance spatial distribution by light-emitting diodes (LEDs) on near... more A method for modeling the irradiance spatial distribution by light-emitting diodes (LEDs) on near distance targets has been developed. The model can easily handle the complex simulation of non-homogenous emitting LEDs, multichip LEDs, LED arrays, and phosphor coated LEDs. The LED irradiation profile is obtained by image processing one photograph of the emitting LED, taken with a smartphone. The method uses image convolution or image correlation between the LED image and a special kernel. The model provides the irradiation spatial pattern in function of the irradiation distance. And the model is tested both with theory and with experimental measurements.
Light-emitting diodes (LEDs) play a major role in many applications where intense light irradiati... more Light-emitting diodes (LEDs) play a major role in many applications where intense light irradiation is necessary. There are several LED radiation pattern models, which are widely used, but are valid only for far-field. In this work, we propose a mathematical model for the spatial distribution of irradiance of LEDs at near working distances.
Ray tracing in a metasurface is the process to obtain the three-dimensional (3D) light path under... more Ray tracing in a metasurface is the process to obtain the three-dimensional (3D) light path under reflection and transmission, which may be helpful in the optical design of metalenses and other metaoptical devices. In this work, first we deduce the 3D vector form of Snell's law for metasurfaces by using a geometric approach. And then, we deduce the general equations to calculate the direction of the reflected and refracted beams in any metasurface, and for any incident beam. In other words, we derive vector form equations for the 3D direction of transmitted and reflected beams at a metasurface with arbitrary 2D phase profile, and for any 3D direction of incident light.
Ray tracing in a metasurface is the process to obtain the three-dimensional (3D) light path under... more Ray tracing in a metasurface is the process to obtain the three-dimensional (3D) light path under reflection and transmission, which may be helpful in the optical design of metalenses and other metaoptical devices. In this work, first we deduce the 3D vector form of Snell's law for metasurfaces by using a geometric approach. And then, we deduce the general equations to calculate the direction of the reflected and refracted beams in any metasurface, and for any incident beam. In other words, we derive vector form equations for the 3D direction of transmitted and reflected beams at a metasurface with arbitrary 2D phase profile, and for any 3D direction of incident light.
Aggregates of superparamagnetic colloids confined in liposomes in the presence of a controllable ... more Aggregates of superparamagnetic colloids confined in liposomes in the presence of a controllable external magnetic field are studied here by computer simulation. A model of a hard sphere with a central dipole has been used to simulate secondary particles of colloids confined to move within a liposome, which is modelled as a hard spherical cavity. We focus our study on the structure of aggregates created by secondary particles, which in turn are formed by superparamagnetic particles. This study was performed by using the conventional Monte Carlo simulations and the cluster-moving Monte Carlo method. The results obtained with both methods show a dependence on the number of particles and on the ratio cavity-colloid diameters. However, the usual Monte Carlo method does not allow the collective movement of the aggregates. The simulation results show, that for the particular case of the liposome diameter obtained from the experiments , the formation of a single ribbons located at the centre of the cavity for N = 30 and N = 60. In addition, we analyse the structure formation for different values of , the equilibrium structures are chains for systems for lower , whereas ribbons formation are structures of equilibrium for . GRAPHICAL ABSTRACT
In this work, we deduce an exact analytical solution of irradiance produced by a Lambertian recta... more In this work, we deduce an exact analytical solution of irradiance produced by a Lambertian rectangular source at short distances, which may approximate the irradiance of a typical light-emitting diode (LED) with rectangular shape.
Many emerging light-emitting diode (LED) applications require short-distance illumination. For th... more Many emerging light-emitting diode (LED) applications require short-distance illumination. For that, we derive an exact formula of the illumination profile produced by Lambertian LEDs, in which all parameters are fundamental constants. Moreover, we propose a general, simple, but accurate mathematical model of the irradiance pattern, valid for Lambertian and non-Lambertian LEDs at short distances. This model provides the irradiance profile as a function of both the LED-target distance and the coordinates of every point on the irradiated surface. The model is formulated in terms of simple sigmoid functions, in which LED size and light flux are fundamental parameters. The accuracy of the irradiance pattern model is tested both with theory and with experimental measurements.
We describe the differential cell design and the experimental (optical and electronic) setup for ... more We describe the differential cell design and the experimental (optical and electronic) setup for the differential front photopyroelectric technique, whose theory has been developed in the first part of this paper (Ivanov et al 2008 J. Phys. D: Appl. Phys. 41 085106). We will show first how the direct (non-differential) front photopyroelectric theory described in our previous paper reproduces well the experimental results. The usefulness of the differential technique is demonstrated by means of experimental measurements of the thermal effusivity in binary ethanol-water and glycerol-water mixtures, based on a theoretical methodology that simplifies the measurement procedure and diminishes the experimental uncertainty.
Ceramic phosphor plates of cerium (Ce 3+) doped oxyfluoride were fabricated by the solid state re... more Ceramic phosphor plates of cerium (Ce 3+) doped oxyfluoride were fabricated by the solid state reaction method. These phosphors exhibit efficient emission, with the novel feature of color tuning by varying both the doping concentration and excitation wavelength. As the Ce 3+ concentration increases, the excitation spectrum broadens by a factor of 1.6, and the excitation peak wavelength shifts from 390 nm to 435 nm, and there is a variation in excitation energy of ~ 10%. Luminescence spectrum of low Ce 3+ concentration samples is tuned from blue to green with the change of excitation wavelength. The emission peak exhibits a shift of 58 nm into the red spectral region, varying the Ce 3+ concentration from 0.05 to 0.1 mol%; while this shift is only 6 nm when Ce 3+ content changes from 0.25 to 1 mol%. Photoluminescence (PL) quantum yield has achieved 76%. The crystal structure was examined using X-ray diffraction to explain its possible influence on the redshift luminescence. A proof of concept of white LED was constructed using a 450 nm blue LED chip with an oxyfluoride phosphor plate, showing a luminous efficacy (LE) of 64 lm/W with a color rendering index of 74.
Latin America Optics and Photonics Conference, 2016
Strong emission of green light in ceramic glass was obtained. The intensity of the emitted signal... more Strong emission of green light in ceramic glass was obtained. The intensity of the emitted signal changes with the heat treatment temperature.
Latin America Optics and Photonics Conference, 2016
Strong green-yellow emission in Eu2+ doped glass ceramic as a function of rare earth concentratio... more Strong green-yellow emission in Eu2+ doped glass ceramic as a function of rare earth concentration was obtained. Proof of concept for solid state white lighting with high power AC LED was fabricated.
Convolutional neural networks (CNNs) and digital holographic interferometry (DHI) can be combined... more Convolutional neural networks (CNNs) and digital holographic interferometry (DHI) can be combined to improve the calculation efficiency and to simplify the procedures of many DHI applications. In DHI, for the measurements of concentration differences between liquid samples, two or more holograms are compared to find the difference phases among them, and then to estimate the concentration values. However, liquid samples with high concentration difference values are difficult to calculate using common phase unwrapping methods as they have high spatial frequencies. In this research, a new method to skip the phase unwrapping process in DHI, based on CNNs, is proposed. For this, images acquired by Guerrero-Mendez et al. (Metrology and Measurement Systems 24, 19–26, 2017) were used to train the CNN, and a multiple linear regression algorithm was fitted to estimate the concentration values for liquid samples. In addition, new images were recorded to evaluate the performance of the proposed...
A multichip light-emitting diode (LED) should not be treated as a point source at short-distance ... more A multichip light-emitting diode (LED) should not be treated as a point source at short-distance illumination. For that, we propose a general, simple, but accurate mathematical model of the irradiance spatial distribution for multichip LEDs, valid at very short distance illumination. This model provides the irradiance profile as a function of both the LED-target distance and the coordinates of every point on the irradiated surface. The model is formulated in function of the chip array geometry, number chips, multichip LED size, and light flux. The accuracy of the irradiance pattern model is tested both with theory and with experimental measurements.
Resumen es: Al planear un experimento con la tecnica fotopiroelectrica, se deben encontrar los pa... more Resumen es: Al planear un experimento con la tecnica fotopiroelectrica, se deben encontrar los parametros adecuados del equipo de medicion para evitar la distorsion ...
We have implemented an exact ray trace through a plano-freeform surface for an incident plane wav... more We have implemented an exact ray trace through a plano-freeform surface for an incident plane wavefront. We obtain two caustic surfaces and provide the critical points related to the ray tracing process. Additionally, we study the propagation of the refracted wavefronts through the plane-curved surface. Finally, by using the Ronchi-Hartmann type null screen and placing the detection plane within the caustic region, we have evaluated the shape of a plano-freeform optical surface under test, obtaining an RMS difference in sagitta value of 6.3 μm.
Light stimulation and biofloc technology can be combined to improve the efficiency and sustainabi... more Light stimulation and biofloc technology can be combined to improve the efficiency and sustainability of tilapia production. A 73-day pilot experiment was conducted to investigate the effect of colored light on growth rates and nutritional composition of the Nile tilapia fingerlings (Oreochromis niloticus) in biofloc systems. The effect of colored light on the nutritional composition of bioflocs as a food source for fish was measured. Three groups were illuminated in addition to natural sunlight with colored light using RGB light emitting diodes (LEDs) with peak wavelengths (λ) of 627.27 nm for red (R), 513.33 nm for green (G), and 451.67 nm for blue (B) light. LED light intensity was constant (0.832 mW/cm 2), and had an 18-h photoperiod of light per day throughout the study. The control group was illuminated only with natural sunlight (natural). Tilapia had an average initial weight of 0.242 g. There was a significant effect of colored light on tilapia growth and composition. The R group showed the best growth rate, highest survival, and highest lipid content. The B group showed homogeneous growth with the lowest growth rate and lipid content, but the highest protein level. On the other hand, the biofloc composition was influenced by the green light in the highest content of lipids, protein, and nitrogen-free extract.
Street lighting, which is one of the main players in energy waste and light pollution at night, s... more Street lighting, which is one of the main players in energy waste and light pollution at night, still faces the challenge of efficient lighting of roadways with curved and twisted shapes. To meet this challenge, we propose an effective and efficient adaptive lightemitting diode (LED) luminaire. This LED lamp delivers a roadway-shape light pattern, which maximizes illumination performance. The light is efficiently and homogeneously directed only where is needed; which reduces glare, and improves both the eye comfort and the visual discrimination ability of car drivers and pedestrians. The proposed luminaire is very practical in that it only requires to replace the cover plate, which is a special microlens array sheet, to produce different shape light patterns. The adaptive mechanism is simple and effective: LED light is first collimated and then efficiently distributed on a freeform roadway by the special microlens sheet. We present an extensive analysis of the lighting adaptability of the proposed luminaire by Monte Carlo ray tracing. In particular, we studied the effect of the main microlens structural parameters in the shape and size of the delivered illumination distribution on the roadway. We present a design example, a prototype construction, and an experimental confirmation on a scale street lighting system. Simulations and experimental results show the advantages of adaptive luminaires over the traditional nonadaptive approaches.
Current Developments in Lens Design and Optical Engineering XIX
To date, many studies on the optimization of the spectral power distributions (SPDs) have been co... more To date, many studies on the optimization of the spectral power distributions (SPDs) have been conducted to maximize the energy performance and color quality of white light-emitting diodes (LEDs). Here, not only for LEDs but for any light source, we numerically calculate the SPDs which maximize luminous efficacy of radiation (LER) in function of the color rendering index and of color temperature. As previously reported in the literature, we obtain optimal SPDs that are discrete spectra rather than continuous, but with considerably higher LER values. Such optimal SPDs may be used to design various lighting technologies: incandescent, fluorescent, high-intensity discharge, laser, and solid-state lighting.
A method for modeling the irradiance spatial distribution by light-emitting diodes (LEDs) on near... more A method for modeling the irradiance spatial distribution by light-emitting diodes (LEDs) on near distance targets has been developed. The model can easily handle the complex simulation of non-homogenous emitting LEDs, multichip LEDs, LED arrays, and phosphor coated LEDs. The LED irradiation profile is obtained by image processing one photograph of the emitting LED, taken with a smartphone. The method uses image convolution or image correlation between the LED image and a special kernel. The model provides the irradiation spatial pattern in function of the irradiation distance. And the model is tested both with theory and with experimental measurements.
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Papers by Ivan Moreno