UVA Fluorescent Lamps Research Articles

Flash Latex Production in a Continuous Helical Photoreactor: Releasing the Brake Pedal on Acrylate Chain Radical Polymerization

The continuous photopolymerization of acrylate and methacrylate monomer miniemulsions (25% solids content) is investigated at room temperature in a compact helix minireactor. Using n-butyl acrylate, the process yields 95% conversion after only 27 s residence time, and gel-free high-molecular-weight products. Under optimized conditions, a 25-fold increase in efficiency is obtained when compared to a batch photopolymerization. The reaction set-up offers a frugal process because of moderate irradiance (2.6 mW cm−2), photoinitiator concentration (0.75 wt%), and low-power UV-A fluorescent lamp.

Correction of nonuniformity error of Gafchromic EBT2 and EBT3.

This study investigates an X‐ray dose measurement method for computed tomography using Gafchromic films. Nonuniformity of the active layer is a major problem in Gafchromic films. In radiotherapy, nonuniformity error is reduced by applying the double‐exposure technique, but this is impractical in diagnostic radiology because of the heel effect. Therefore, we propose replacing the X‐rays in the double‐exposure technique with ultraviolet (UV)‐A irradiation of Gafchromic EBT2 and EBT3. To improve the reproducibility of the scan position, Gafchromic EBT2 and EBT3 films were attached to a 3‐mm‐thick acrylic plate. The samples were then irradiated with a 10 W UV‐A fluorescent lamp placed at a distance of 72 cm for 30, 60, and 90 minutes. The profile curves were evaluated along the long and short axes of the film center, and the standard deviations of the pixel values were calculated over large areas of the films. Paired t‐test was performed. UV‐A irradiation exerted a significant effect on Gafchromic EBT2 (paired t‐test; p=0.0275) but not on EBT3 (paired t‐test; p=0.2785). Similarly, the homogeneity was improved in Gafchromic EBT2 but not in EBT3. Therefore, the double‐exposure technique under UV‐A irradiation is suitable only for EBT2 films.PACS number(s): 87.53 Bn

The synergistic effect of TiO2 and H5PW10V2O40 in photocatalysis as a function of the irradiation source

This work examined the use of pure TiO2, pure heteropolyacid (HPA) H5PW10V2O40 and TiO2+H5PW10V2O40 catalysts in the photocatalytic decomposition of dimethyl sulfide (DMS) in the gas phase. DMS was irradiated with visible light from an LED (λ>400nm), black light UV-A (λ<400nm) and visible fluorescent lamp ‘daylight’ (variable emission in the UV-A and visible range). DMS decomposition reached almost 100% for the system containing the TiO2+H5PW10V2O40 mixed catalyst with exposure to visible daylight. This system maintained stable catalytic activity up to 500min. These results strongly suggest that a positive synergistic effect occurred between TiO2 and HPA when visible daylight was used.

Fluorescence Imaging with UV-Excitation for Evaluating Freshness of Rice

To measure the freshness of rice quickly and conveniently, we used a fluorescence imaging method with UV-excitation. The system consists of two UV-A fluorescent lamps and a blue LED with a band-pass filter, a cooled CCD camera with an IR cutoff filter to capture the fluorescence image on a PC, and image processing software for measuring the fluorescence intensity of the image. In a darkened box, sample materials are placed on a stage painted with non-fluorescent, flat black paint to minimize background scattering. Testing stored samples of unhulled rice and brown rice, we found a high correlation between the fluorescence intensity and conventional indices such as free fat acidity and guaiacol reaction. The fluorescence intensity increased as the storage temperature rose or the storage period lengthened. Eating quality decreased significantly as the fluorescence intensity rose. These results show that this system can estimate the loss of eating quality that occurs during storage of rice. Thus, fluorescence intensity could provide an effective and convenient way to evaluate rice quality.

Ultraviolet A dosimetry in photopatch test centres in Europe

The aim of the study was to investigate the state of ultraviolet (UV) A dosimetry in photopatch testing centres in Europe. It has been acknowledged that a widespread disparity exists in the way photopatch testing is carried out in different countries throughout Europe. This prompted the formation of a European taskforce that developed a consensus methodology. One issue that was not addressed directly was that of UVA dosimetry, which clearly impacts on the consistency of the clinical results. Ten UV meters from photopatch test centres throughout Europe were set up at a reproducible position from a photopatch test light source containing UVA fluorescent lamps and the irradiances were noted from each meter. One meter served as a reference meter with calibration carried out in an optical laboratory traceable to the National Physical Laboratory. The mean of all the measurements was 5.74 mW/cm(2) with a SD of 0.36 mW/cm(2). Expanded uncertainty at 95% confidence level was 12%. It is desirable that meter calibration should have an accuracy of the order of +/-10%. The variation in recorded values among the 10 meters investigated was within acceptable limits. The meter must be calibrated using a similar light source to that used in the phototest equipment, in this case a UVA fluorescence lamp.

Photosensitized degradation of Irgarol 1051 in water

Irgarol 1051 (2-methylthio-4- tert-butylamino-6-cyclopropylamino- s-triazine) is a herbicide analogue that is added to antifouling agents used on ships. Our former study on its degradation in sunlight suggested that unknown photosensitizers in natural waters accelerated the photodegradation to the degradation product, M1. In this study, the photodegradation of Irgarol in water was investigated in the presence of some photosensitizers. Test water containing Irgarol or M1, with or without photosensitizers, was irradiated with light from a UV-A fluorescent lamp for 48 h. The concentrations of Irgarol and M1 in the test water were determined by HPLC after solid-phase extraction. M1 was more stable than Irgarol when irradiated in the presence of photosensitizers such as acetone, benzophenone, tryptophan, and rose bengal. Hydrogen peroxide (HP) accelerated the photodegradation of Irgarol, and the product M1 was degraded in the presence of more than 100 mg l −1 HP after 10 h. Natural humic substances (NHS) also accelerated the photodegradation of Irgarol, but in this case, the product M1 persisted even when Irgarol was completely degraded. Photosensitized degradation of Irgarol by NHS may result in the accumulation of M1 in aquatic environments.

The Effect of Solar Irradiation on the Fading of Nylon and Polyester Fabrics Dyed with Selected Disperse Dyestuffs on Radiant Energy Basis

Solar total, UVA and UVB irradiances were measured separately using three kinds of wavelength band detectors in Tokyo, Japan in November 1999. Characteristics of diurnal variations were examined: Total irradiance reached a maximum value of about 600 W m-2 at around noon. The variation pattern of UVA irradiance was observed to be similar to the total irradiance. The energy level was about 4.65 % of total irradiance. Diurnal variation of UVB was in the form of a steeper bell curve due to the absorption in the air mass. UVB energy to solar total irradiance was about 0.07%. Photodegradation characteristics of two disperse dyestuffs were investigated on the basis of solar radiant energy. A UVA fluorescent lamp was applied to examine the fading characteristics to find the wavelength dependency. As a result, nylon dyeings were less lightfast by a factor of about 6 and 13 for C I Disperse Blue 27 and C I Disperse Blue 165, respectively, compared with polyester on the radiant energy basis. Visible light, as well as UVA, radiation contribute to fading of C I Disperse Blue 165 whereas UVA mostly cause the fading of C I Disperse Blue 27.

Characteristics of fading of wool cloth dyed with selected natural dyestuffs on the basis of solar radiant energy

Photodegradation characteristics of selected natural dyestuffs were investigated on the basis of solar radiant energy. UVA and UVB fluorescent lamps were also applied to examine wavelength dependencies on the fading characteristics. The natural dyestuffs were observed to have poorer lightfastness in the comparison with AATCC Blue Wool L2. The order of fading susceptibility to solar radiation is as follows: Turmeric > Weld > Madder > L2. Moreover, It was concluded that the natural dyestuffs were strongly sensitive to visible light as well as to UV rays and L2 would be faded by visible light to the small extent. These results provide an important key to understanding the poor lightfasteness of some natural dyestuffs.

Photochemical and oxidative degradation of the solid-state tretinoin tocoferil.

The photostability of tretinoin tocoferil was investigated under irradiation with three kinds of lamps, i.e., a cool white fluorescent lamp, a UV-A fluorescent lamp and a D65 fluorescent lamp. A combination of the cool white fluorescent lamp and the UV-A fluorescent lamp, and the D65 lamp having relative spectral power distribution similar to that of direct daylight, correspond to options 2 and 1 in ICH Guidelines, respectively. The photodegradation apparently followed second-order kinetics under these light sources and the degradation rate constant under exposure by the D65 lamp was larger than that by the cool white fluorescent lamp. The drug was susceptible to degradation by visible and UV light below 480 nm and was degraded most remarkably at around 420 nm, showing a wavelength-dependency. The semi-logarithmic plots of apparent degradation rate constant against the reciprocal of illuminance showed a good linear relationship in the Arrhenius-type fashion, and the photostability under ordinary illumination conditions could be predicted from the data obtained under the accelerated illumination conditions. The rate of oxidative degradation was slightly accelerated with the rise of temperature. Thermodynamic parameter was calculated from the Arrhenius plot. The degradation rate constant rapidly increased in proportion to partial pressure of oxygen below 20 kPa.

Prediction of minimal erythema dose with a reflectance melanin meter

The relationship between skin pigmentation and sensitivity to ultraviolet (UV) radiation-induced erythema was investigated in 60 healthy subjects of sun-reactive skin types I-V. Using a portable reflectance spectrometer, skin pigmentation was measured as the 'melanin index' (MI) in all subjects. A solar-simulated array of filtered UVA and UVB-emitting fluorescent lamps was then used to determine the UVB minimal erythema dose (MED) of each subject. MI readings and MED testing were both performed on the subjects' mid to upper backs. Using this technique, we found a close correlation between MI and MED. Comparison of the mean MI or MED of subjects with different skin types revealed progressive differences in MI and MED between all five skin types. Erythema dose-response curves, which provide further information about UV sensitivity, were also calculated for 43 subjects. A significant negative correlation was found between the gradients of these curves and both MI and MED, indicating that paler subjects respond more strongly to increments of UV above the MED than subjects with greater pigmentation. Our results indicate that although traditional, subjective means of predicting UV sensitivity to erythema are not without some value, MED correlates particularly strongly with objective measures of skin pigmentation. We therefore conclude that the reflectance spectrometer can rapidly and accurately predict UVB sensitivity, and should prove clinically useful for planning and optimizing UVB phototherapy.

The UVB content of 'UVA fluorescent lamps' and its erythemal effectiveness in human skin

The UBV emission from ten different types of 'UVA fluorescent lamp' has been measured by spectroradiometry. The mean ratio of UVB emission to UVA emission was found to be 0.94+or-0.35 (1 SD)%. By weighting the spectral irradiance of each lamp by the DIN standard erythemal curve, the mean erythemally effective UVB emission (normalised to 297 nm), expressed as a percentage of the UVA emission, was 0.076+or-0.049 (1 SD)%.