Polychromatic Lamp Research Articles

Heterostructured g-C3N4-TiO2 nanocomposites applied to p-toluic acid degradation under solar light-induced photocatalytic process

In this work, heterostructured photocatalysts were prepared with TiO2-P25 nanocrystals dispersed on two-dimensional layers of g-C3N4. Different g-C3N4:TiO2 ratios (25 %, 50 % and 75 %) were prepared using a wet method under ultrasonic exfoliation and thermal treatment under an oxidizing atmosphere. The heterojunctions were confirmed by X-ray diffraction, and electron microscopy, showing TiO2 nanocrystals anchored onto the surface of the g-C3N4 structure. The obtained heterojunctions increased light absorption from the ultraviolet to the visible spectrum and reduced the recombination of photoinduced charge carriers confirmed by photoluminescence and band gap energy (Eg) measurements. The photocatalytic performance was evaluated in the degradation of p-toluic acid (p-TA) (20 mg L–1) under UVA LED at 365 nm, a polychromatic lamp (UVA-UVB-visible) and solar radiation. The g-C3N4:TiO2 ratio of 25 % showed the best performance, reaching 95 % degradation after 180 min under solar radiation. The reuse tests showed that the mineralization capacity determined by total organic carbon (TOC) remained stable for 6 cycles, achieving 80.8 % TOC degradation. The heterojunction induced a significant alteration in the rheological behavior of the suspension, which made the g-C3N4-TiO2 easily recoverable, unlike the pure TiO2. The radical scavengers study indicated that the superoxide anion radical (O2•–) is the main oxidative species in p-TA photodegradation on g-C3N4-TiO2 photocatalyst. The greatest advantage of the g-C3N4 in the composite was the absorption of light in the visible range and facile catalyst recovery for reuse while presenting photocatalytic activity similar to TiO2.

Wavelength trends of photoproduction of reactive transient species by chromophoric dissolved organic matter (CDOM), under steady-state polychromatic irradiation

The formation quantum yields of photochemically produced reactive intermediates (PPRIs) by irradiated CDOM (in this study, Suwannee River Natural Organic Matter and Upper Mississippi River Natural Organic Matter) decrease with increasing irradiation wavelength. In particular, the formation quantum yields of the excited triplet states of CDOM (3CDOM*) and of singlet oxygen (1O2) have an exponentially decreasing trend with wavelength. The •OH wavelength trend is different, because more effective •OH production occurs under UVB irradiation than foreseen by a purely exponential function. We show that the parameter-adjustable Weibull function (which adapts to both exponential and some non-exponential trends) is suitable to fit the mentioned quantum yield data, and it is very useful when CDOM irradiation is carried out under polychromatic lamps as done here. Model calculations suggest that, thanks to the ability of CDOM to also absorb visible radiation, and despite its decreasing quantum yield of •OH generation with increasing wavelength, CDOM would be able to trigger •OH photogeneration in deep waters, to a higher extent than UVB-absorbing nitrate or UVB + UVA-absorbing nitrite.

Effect of Irradiation on Structural Changes of Levan

Levan, as a biocompatible and renewable biopolymer with anticancer properties, is a promising candidate for a wide range of applications in various fields of industry. However, in the literature, there is a lack of information about its behavior under the influence of UV irradiation, which may limit its potential application, including medical science. Therefore, this study describes the effects of irradiation on the structural properties of levan. This type of fructan was subjected to stability tests under radiation conditions using LED and polychromatic lamps. The results showed that the photodegradation of levan irradiated with a polychromatic light occurs faster and more efficiently than the photodegradation of levan irradiated with an LED lamp. Furthermore, AFM analysis showed that the surface became smoother after irradiation, as evidenced by decreasing values of roughness parameters. Moreover, UV irradiation causes the decrease of total surface free energy and both its components in levan; however, more significant changes occur during irradiation of the sample with a polychromatic lamp.

Épilation par lasers et lampes

Regardless of the actual method used, depilation is a process that has been present since antiquity and is found across all the continents. Thanks to the recent introduction of pulsed polychromatic lamps and lasers, long-lasting depilation is now possible. This article describes the theoretical basis for this new technology and discusses the various types of equipment available. Whether such devices are used for aesthetic or medical reasons, doctors must have a knowledge of the various techniques involved, as well as the limitations thereof. They must also be able to manage all potential adverse effects arising during or after depilation sessions.

Realization of the Radiance Scale Using Transfer Function of the Laser-Based Optical System

This work aims to determine the radiance responsivity to be used in the calibration of polychromatic radiation sources with low uncertainty. To realize the radiance, Ar-ion, He-Ne, and Nd-YAG lasers as well as an integrating sphere with a 0.15 m diameter are used to obtain radiation sources having Lambertian distributions. Then, a silicon photodiode-based reflection-type trap detector with calibrated precision aperture, which is traceable to a liquid helium cooled laser-based cryogenic radiometer, is used to measure the photocurrent corresponding to each wavelength and thereby to obtain radiance. The proposed system, which measures the spectral current response of this laser-based radiance, is a double-grating monochromator with a 2 × 300 mm focal length and triple gratings in each of its turrets. First, the radiance of the laser beam that emerged from the integrating sphere is calculated, and then the radiance responsivity of the system is obtained by measuring the photocurrent outputted from the exit slit of the monochromator at each laser wavelength. Finally, the spectral radiance values of the polychromatic lamps are obtained using the radiance responsivity of the system. Consequently, the study aims to develop the derivation and better understand traceability of the other radiometric and photometric quantities with low uncertainty from the fundamental radiometric radiance unit. Measurement results obtained in the expanded measurement uncertainty scale are determined using both classical and Monte Carlo methods.

The involvement of superoxide radicals in medium pressure UV derived inactivation

Today, two types of lamp systems dominate the UV disinfection industry: low-pressure (LP) UV lamps and medium-pressure (MP) polychromatic lamps. Both lamp types have their advantages and disadvantages in microorganism inactivation, with LP lamps being cheaper, having longer life, and working at lower temperature, hence reducing fouling, and MP lamps showing better inactivation per germicidal dose for certain microorganisms. Bacterium-based biosensors were used to compare LP and MP irradiation. These biosensors were Escherichia coli bacteria carrying the lux operon genes under the control of different stress-responding promoters, where activation of the specific promoter is manifested as bioluminescence. MP irradiation, considerably more than LP irradiation, resulted in activation of the superoxide dismutase expression, indicating the formation of superoxide radicals inside the cells. Accordingly, pre-exposure (immunization) of the bacteria to an activator that produces superoxide radicals resulted in lower inactivation and increased resistance to MP irradiation, but not to LP irradiation. This study shows that the difference in germicidal efficiency may result from the production of intracellular superoxide radicals by MP irradiation, at wavelengths other than 254 nm, as emitted by LP lamps.

Increasing color saturation by optimizing light spectra constrained on color rendering properties

Enhancing the color saturation of objects via illumination with specially designed light spectra is promising in many commercial and scientific applications. Existing literature has focused on studying the colors that can be rendered by white light with various correlated color temperatures, and by the mixed light from various monochromatic light-emitting diodes. However, very little literature has been devoted to methods that can actively configure the light spectrum to enhance the color saturation of an arbitrary object. This paper proposes an optimization-based method to extend the gamut that can be achieved by a given polychromatic lamp toward a chosen direction, i.e., to increase the saturation of a specific color. Moreover, to trade-off the increased saturation of a color sample with the reduced colorfulness of other samples, constraints with tunable thresholds are imposed to the optimization problem to bound the variation of a contrast color sample. In addition, the effect of uncontrollable ambient light can be taken into account by mild modifications of the optimization problem. Simulation results show that the optimized light spectrum can effectively enhance the saturation of any specific color, while maintaining the other rendered colors as intact as possible. Visual experiments have also been conducted with 22 human subjects, whose responses agree with the simulation results.

Optimization of LED light spectrum to enhance colorfulness of illuminated objects with white light constraints

Enhancing the colorfulness of illuminated objects is a promising application of LED lighting for commercial, exhibiting, and scientific purposes. This paper proposes a method to enhance the color of illuminated objects for a given polychromatic lamp. Meanwhile, the light color is restricted to white. We further relax the white light constraints by introducing soft margins. Based on the spectral and electrical characteristics of LEDs and object surface properties, we determine the optimal mixing of the LED light spectrum by solving a numerical optimization problem, which is a quadratic fractional programming problem by formulation. Simulation studies show that the trade-off between the white light constraint and the level of the color enhancement can be adjusted by tuning an upper limit value of the soft margin. Furthermore, visual evaluation experiments are performed to evaluate human perception of the color enhancement. The experiments have verified the effectiveness of the proposed method.

Biofouling control in water by various UVC wavelengths and doses

UV light irradiation is being increasingly applied as a primary process for water disinfection, effectively used for inactivation of suspended (planktonic) cells. In this study, the use of UV irradiation was evaluated as a pretreatment strategy to control biofouling. The objective of this research was to elucidate the relative effectiveness of various targeted UV wavelengths and a polychromatic spectrum on bacterial inactivation and biofilm control. In a model system using Pseudomonas aeruginosa, the inactivation spectra corresponded to the DNA absorption spectra for all wavelengths between 220 and 280 nm, while wavelengths between 254 nm and 270 nm were the most effective for bacterial inactivation. Similar wavelengths of 254-260-270 nm were also more effective for biofilm control in most cases than targeted 239 and 280 nm. In addition, the prevention of biofilm formation by P. aeruginosa with a full polychromatic lamp was UV dose-dependent. It appears that biofilm control is improved when larger UV doses are given, while higher levels of inactivation are obtained when using a full polychromatic MP lamp. However, no significant differences were found between biofilms produced by bacteria that survived UV irradiation and biofilms produced by control bacteria at the same microbial counts. Moreover, the experiments showed that biofilm prevention depends on the post-treatment incubation time and nutrient availability, in addition to targeted wavelengths, UV spectrum and UV dose.

Phase Delaying the Human Circadian Clock with Blue-Enriched Polychromatic Light

The human circadian system is maximally sensitive to short-wavelength (blue) light. In a previous study we found no difference between the magnitude of phase advances produced by bright white versus bright blue-enriched light using light boxes in a practical protocol that could be used in the real world. Since the spectral sensitivity of the circadian system may vary with a circadian rhythm, we tested whether the results of our recent phase-advancing study hold true for phase delays. In a within-subjects counterbalanced design, this study tested whether bright blue-enriched polychromatic light (17000 K, 4000 lux) could produce larger phase delays than bright white light (4100 K, 5000 lux) of equal photon density (4.2×1015 photons/cm2/sec). Healthy young subjects (n = 13) received a 2 h phase delaying light pulse before bedtime combined with a gradually delaying sleep/dark schedule on each of 4 consecutive treatment days. On the first treatment day the light pulse began 3 h after the dim light melatonin onset (DLMO). An 8 h sleep episode began at the end of the light pulse. Light treatment and the sleep schedule were delayed 2 h on each subsequent treatment day. A circadian phase assessment was conducted before and after the series of light treatment days to determine the time of the DLMO and DLMOff. Phase delays in the blue-enriched and white conditions were not significantly different (DLMO: −4.45±2.02 versus −4.48±1.97 h; DLMOff: −3.90±1.97 versus −4.35±2.39 h, respectively). These results indicate that at light levels commonly used for circadian phase shifting, blue-enriched polychromatic light is no more effective than the white polychromatic lamps of a lower correlated color temperature (CCT) for phase delaying the circadian clock. (Author correspondence: ceastman@rush.edu)

Phase advancing the human circadian clock with blue-enriched polychromatic light

Background Previous studies have shown that the human circadian system is maximally sensitive to short-wavelength (blue) light. Whether this sensitivity can be utilized to increase the size of phase shifts using light boxes and protocols designed for practical settings is not known. We assessed whether bright polychromatic lamps enriched in the short-wavelength portion of the visible light spectrum could produce larger phase advances than standard bright white lamps. Methods Twenty-two healthy young adults received either a bright white or bright blue-enriched 2-h phase advancing light pulse upon awakening on each of four treatment days. On the first treatment day the light pulse began 8 h after the dim light melatonin onset (DLMO), on average about 2 h before baseline wake time. On each subsequent day, light treatment began 1 h earlier than the previous day, and the sleep schedule was also advanced. Results Phase advances of the DLMO for the blue-enriched (92 ± 78 min, n = 12) and white groups (76 ± 45 min, n = 10) were not significantly different. Conclusion Bright blue-enriched polychromatic light is no more effective than standard bright light therapy for phase advancing circadian rhythms at commonly used therapeutic light levels.

Changes in Optical Properties Caused by UV-Irradiation of Aquatic Humic Substances from the Amazon River Basin: Seasonal Variability Evaluation

Aquatic humic substances (AHS) isolated from two characteristic seasons of the Negro river, winter and summer corresponding to floody and dry periods, were structurally characterized by 13C nuclear magnetic ressonance. Subsequently, AHS aqueous solutions were irradiated with a polychromatic lamp (290-475 nm) and monitored by its total organic carbon (TOC) content, ultraviolet-visible (UV-vis) absorbance, fluorescence, and Fourier transformed infrared spectroscopy (FTIR). As a result, a photobleaching up to 80% after irradiation of 48 h was observed. Conformational rearrangements and formation of low molecular complexity structures were formed during the irradiation, as deduced from the pH decrement and the fluorescence shifting to lower wavelengths. Additionally a significant mineralization with the formation of CO2, CO, and inorganic carbon compounds was registered, as assumed by TOC losses of up to 70%. The differences in photodegradation between samples expressed by photobleaching efficiency were enhanced in the summer sample and related to its elevated aromatic content. Aromatic structures are assumed to have high autosensitization capacity effects mediated by the free radical generation from quinone and phenolic moieties.

Assessment of Reduction Equivalent Fluence Bias Using Computational Fluid Dynamics

A study was performed to investigate the use of computational fluid dynamics (CFD) coupled with a fluence rate model to determine the bias in UV biodosimetry measurements using inactivation of a challenge microbe instead of the target pathogen—termed the reduction equivalent fluence (REF) bias. Simulations were performed using two fluence rate models: RADial Line Source Integration (RADLSI), and UVCalc3D, a multiple segment source summation (MSSS). CFD UV models were carried out in several closed-conduit UV reactors using either mono- or polychromatic lamps. Simulations were also performed with different UV transmittances, flow rates, lamp power settings, and with lamps out of service. In addition, the Cryptosporidium fluence response kinetics was approximated using two nonlinear models: a P-factor model, and a Rational model. The REF bias was computed using the predicted fluence distribution from a Lagrangian particle tracking routine and compared with the REF bias computed using the EPA UV disinfection ...

Effects of the H2O2 concentration and spectral distribution of the UV lamp output power on the photooxidation of a water pollutant

Previous kinetics studies have been extended to analyze some practical issues concerning this process. Hence, in this work we have studied additional aspects of the H2O2 enhanced, UV degradation of 2,4-dichlorophenoxyacetic acid (2,4-D), namely: (i) the effect of the H2O2/2,4-D initial molar ratio and (ii) the effect of the irradiation power and, particularly, the characteristics of the wavelength distribution of the lamp output emission. The work was done on a well stirred, discontinuously operated tank reactor irradiated from its bottom. A UV, tubular lamp and a cylindrical reflector of parabolic cross section were used [actually, two germicidal lamps (254 nm) of different output power per unit lamp length and a medium pressure, mercury arc lamp with polychromatic emission between 220 and 760 nm]. 2,4-D concentration and TOC were the main variables used to investigate the degradation rate. There is an optimal initial concentration ratio for each 2,4-D initial concentration. It was also observed that increasing the lamp output power at 254 nm (output from 0.08 W/cm to 0.6 W/cm) favors the reaction rate. However, much more significant is the effect produced by employing a polychromatic lamp with some emission below 254 although this photonic contribution is relatively small (just 0.21 W/cm below 250 nm). A kinetic model, having parameters independent of the reactor configuration and derived from mechanistic considerations was used to analyze the experimental data.

Survival of Cloudman mouse melanoma cells after irradiation by solar wavelengths of light.

A number of variants of Cloudman S91 mouse melanoma cells that differ with respect to the amount of pigment produced are available for study. In this report, we compare the photobiological responses of S91/amel, which contains about 1 pg of melanin per cell, with S91/I3, which contains about 3 pg/cell. Earlier studies had shown that UVC induced more oxidative damage (in the form of thymine glycols) in cell line S91/I3 than in S91/amel and that cell line S91/amel was more resistant to killing by UVC than S91/I3. The present study finds that S91/amel cells are also relatively resistant to killing by near monochromatic UVB from a Philips TL01 fluorescent lamp and by near monochromatic UVA from a Philips HPW125 lamp. However, when the cells are irradiated with a Westinghouse FS20 polychromatic lamp, the S91/I3 cells are more resistant than the S91/amel cells. These findings cannot be explained on the basis of pigment induction because in S91/I3 this is about the same after UVB and FS20, although the maximum is reached earlier after UVB. Nor can our findings be explained on the basis of pyrimidine dimer formation, which is comparable in the two cell lines regardless of the type of irradiation. These results suggest that, with a pigment such as melanin, which absorbs light across the visible and ultraviolet ranges of the spectrum, cellular responses to monochromatic light do not necessarily predict responses to polychromatic mixtures.

F-Specific RNA Bacteriophages as Model Viruses in UV Disinfection of Wastewater

F-specific RNA (FRNA) bacteriophages can be assayed in wastewater by simple and rapid methods. Their inactivation by UV radiation follows first-order kinetics and relatively simple formulas can describe the effect of UV absorbance by wastewater and the wavelength-dependent killing efficiency of polychromatic lamps. Because the organisms can be grown in high concentrations, biological calibration of full-scale reactors requires only relatively small volumes of phage culture. Naturally occurring FRNA-phages were more resistant to UV than somatic coliphages, Escherichiacoli and faecal streptococci. The inactivation rate constant was almost equal to that of reoviruses, which underlines the suitability of FRNA-phages as a process indicator for UV inactivation of viruses. A pure culture of MS2 was inactivated at a rate which was almost twice that of naturally occurring FRNA-phages, indicating the necessity of designing reactors for practical applications on field-data rather than laboratory experiments.

Inactivation rate of Bacillus subtilis spores irradiated by ultraviolet rays.

The UV inactivation of Bacillus subtilis spores, widely used for examining sterility, was kinetically studied to obtain fundamental information on the design and performance evaluation of practical sterilizers irradiated by ultraviolet rays. The inactivation rate at low extent of sterilization (survival fraction of more than 10-2) was determined under monochromatic irradiation and analyzed by the single-hit-killing model based on the target theory. The inactivation cross-section, φa, was strongly dependent on wavelength; the target number, m, was rather constant from 240 through 300 nm. The inactivation characteristics at high extent of conversion (survival fraction of less than 10-3) under polychromatic irradiation were simulated by considering the presence of a small portion of UV-resistant spores. An improved kinetic model was derived on the assumption of coexistence of two types of spores with different inactivation cross-sections and with the same target number. The observed wavelength-averaged inactivation cross-section for the major portion of spores was evaluated from both the inactivation cross-section obtained with monochromatic irradiation and the spectral distribution of light emitted from a polychromatic lamp.

Photodecomposition of 2,4-dichlorophenoxyacetic acid

Three types of reactor operation, flow-differential, flow-integral, and batch-recycle were employed to study the kinetics of the photolysis and oxidation of 2,4-dichlorophenoxyacetic acid (2,4-D). The flow-through annular reactor was irradiated with a polychromatic lamp located at the axis of the annulus. Using aqueous solutions of pollutant-level concentrations (5-50 ppm), the initial rate was found proportional to the light abosrbed and otherwise independent of 2,4-D and dissolved oxygen concentrations. Using thin-layer chromatographic and spectroscopic analytical methods, 2,4-dichlorophenol (2,4-DCP) was identified as one of the photolysis products. Measurements were also made of the initial rate and rate at finite conversions for 2,4-DCP. The results were consistent with a rate equation based upon a photo-activation process followed by formation of peroxides. Of particular significance was the autocatalytic effect of intermediates on the rate of disappearance of 2,4-D. One such catalytic agent was 2,4-DCP. Carbon dioxide was produced as the final oxidation product when either 2,4-D or 2,4-DCP was the reactant. The amount of CO 2 formed proved that the aromatic ring was ruptured. This suggests the possibility of employing photochemical oxidation for reducing refractory, aromatic pollutants into fragments more susceptible to biological oxidation.