Low UVA Research Articles

Continuum of light sensitivity in atopic dermatitis: A retrospective analysis of 139 cases in Scotland

BackgroundPrevious reports have characterized photosensitivity in atopic dermatitis (AD), but with differences in terminology and criteria. ObjectiveThis study aims to assess outcomes in 139 AD patients referred for photodiagnostic testing and to establish diagnostic criteria for photosensitivity in AD. MethodsClinical and photodiagnostic data were reviewed, categorizing photosensitivity into Photo-Exacerbated AD (PEAD), Photo-Sensitive AD (PSAD), and Chronic Actinic Dermatitis (CAD). ResultsOf the patient cohort, mean age was 42.6±16.7 years and 61.9% were male. PEAD patients (51.1%) had normal monochromator phototesting. PSAD patients (7.9%) displayed slight-to-moderate UVA sensitivity (≥30% of normal minimal erythema dose [MED]) and mostly normal/slightly reduced UVB MEDs (≥80% of normal MED). Conversely, 41% of patients had CAD and 93% of this group demonstrated significant UVB sensitivity, with very low UVB MEDs (<80% of normal MED) and/or very low UVA MEDs (<30% of normal MED). No significant differences in sex, age, or skin phototype were observed between groups. Serial phototesting revealed changes in photosensitivity status over time in eight patients. LimitationsSmall sample size and retrospective design. ConclusionsThis study highlights the heterogeneity of photosensitivity patterns in AD patients and the importance of follow-up assessments due to potential shifts in disease spectrum over time.

From rust to robust disinfectants: How do iron oxides and inorganic oxidants synergize with UVA light towards bacterial inactivation?

Pathogens in drinking water remain a challenge for human health, photo-Fenton process is a promising technique for pathogen inactivation, herein, two common iron oxides, hematite and magnetite mediate persulfate (peroxymonosulfate-PMS - and peroxydisulfate-PDS) involved photo-Fenton-like processes were constructed for E. coli inactivation, and the inactivation performance was investigated and compared with the photo-Fenton process under a low intensity UVA irradiation. Results indicated that with a low dose of iron oxides (1 mg/L) and inorganic peroxides (10 mg/L), PMS-involved photo-Fenton-like process is the best substitute for the photo-Fenton one over pH range of 5–8. In addition, humic acid (HA, one of the important components of natural organic matter) incorporated iron oxide-mediated photo-Fenton-like processes for bacteria inactivation was also studied, and facilitating effect was found in UVA/hematite/PMS and UVA/magnetite/PDS systems. Reactive oxygen species (ROS) exploration experiments revealed that ·OH was the predominant radical in H2O2- and PDS-containing systems, whereas 1O2 was one of the principal reactive species in the PMS systems. In addition to the semiconductor photocatalysis of iron oxides and UVA-activated oxidants, iron-complexes (iron-oxidant complexes and iron-bacteria complexes) mediated ligand-to-metal charge transfer (LMCT) processes also made contribution to bacterial inactivation. Overall, this study demonstrates that it is feasible to replace H2O2 with PMS in a photo-Fenton-like process for water disinfection using a low dose of reagents, mediated by cheap catalysts, such as hematite and magnetite, it is also hoped to provide some insights to practical water treatment.

Sunscreen Safety and Efficacy for the Prevention of Cutaneous Neoplasm.

Sunscreen is widely used for ultraviolet radiation protection. Studies validate sun protection factors (SPFs) to prevent ultraviolet (UV)-induced skin changes such as melanoma and squamous cell carcinoma (SCC). Few studies examine sunscreen's impact on endocrine and immune system dysregulation, the production of radical oxygen species, and whether the ingredients deteriorate under prolonged exposure. We present an investigation of sunscreen labels and how ingredients impact sun safety and human health. A review of the literature was conducted using Embase and PubMed to examine sunscreen safety, efficacy, and use to prevent UV-induced skin damage. Increasing sunscreen reapplication, wearing protective clothing, and limiting exposure can reduce the incidence of skin cancer. Inorganic sunscreens form barriers to block UV light, but without titanium dioxide (TiO2), they may not be advantageous due to their low UVA protection. Organic sunscreens absorb into the skin and provide a better feeling after application. Octocrylene and avobenzone are stable and provide UVA and UVB protection with minimal adverse effects. Oxybenzone is harmful to the neuroendocrine system and should be avoided. Titanium dioxide works for broad-spectrum UV protection and offers minimal adverse effects. Octocrylene and avobenzone are organic sunscreen ingredients that also provide a better feeling on the skin after application, which enables higher rates of use. Oxybenzone should be avoided.

Low voltage drop AlGaN UV-A laser structures with transparent tunnel junctions and optimized quantum wells

This paper presents the design, material growth and fabrication of AlGaN laser structures grown by plasma-assisted molecular beam epitaxy. Considering hole transport to be the major challenge, our ultraviolet-A diode laser structures have a compositionally graded transparent tunnel junction, resulting in superior hole injection and a low contact resistance. By optimizing active region thickness, a five-fold improvement in photoluminescence intensity is obtained compared to that of our own non-optimized test structures. The electrical and optical characteristics of processed devices demonstrate only spontaneous emission with a peak wavelength at 354 nm. The devices operate up to a continuous-wave current density of 11.1 kA cm−2 at room temperature, which is the highest reported for laser structures grown on AlGaN templates. Additionally, they exhibit a record-low voltage drop of 8.5 V to achieve this current density.

1175 Impact of low dose UVA radiation on UVB radiation-induced DNA damage and skin carcinogenesis

1175 Impact of low dose UVA radiation on UVB radiation-induced DNA damage and skin carcinogenesis

Role of Pel and Psl polysaccharides in the response of Pseudomonas aeruginosa to environmental challenges: oxidative stress agents (UVA, H2O2, sodium hypochlorite) and its competitor Staphylococcus aureus.

Pseudomonas aeruginosa is a versatile bacterium capable of adapting to a wide range of stress factors, including solar UVA radiation (400-315 nm). High UVA doses produce lethal effects due to the action of reactive oxygen species. Sublethal UVA doses also induces oxidative damage, but, in addition, it triggers a variety of adaptive responses, including the overexpression of pelA and pslA genes in P. aeruginosa. These genes encode the synthesis of Pel and Psl, which are essential polysaccharides in biofilm formation. The present study analysed the role of Pel and Psl in the adaptive responses generated by exposure to low UVA doses, and their importance in the response to lethal doses of UVA, hydrogen peroxide (H2O2), and sodium hypochlorite, in both planktonic cells and submerged and air-liquid interface (ALI) biofilms. It also studied the roles of Pel and Psl in P. aeruginosa-Staphylococcus aureus interaction. The results demonstrate that the capacity of sublethal UVA exposure to increase cell hydrophobicity and cell attachment and generate cross-protection phenomena in P. aeruginosa depends on the presence of Pel and Psl. The study also shows that Pel and Psl have a key role in the tolerance to lethal doses of UVA radiation, sodium hypochlorite and H2O2, in both biofilms and planktonic cells. Finally, co-culture assays showed total inhibition of S. aureus growth in presence of P. aeruginosa. This phenomenon depends, at least in part, on the simultaneous presence of Pel and Psl in planktonic cells and biofilms, suggesting a relevant role of these polysaccharides in the interaction between these species.

Flexible, disposable photocatalytic plastic films for the destruction of viruses.

A thin, 30 μm, flexible, robust low-density polyethylene, LDPE, film, loaded with 30 wt% P25 TiO2, is extruded and subsequently rendered highly active photocatalytically by exposing it to UVA (352 nm, 1.5 mW cm−2) for 144 h. The film was tested for anti-viral activity using four different viruses, namely, two strains of Influenza A Virus (IAV), WSN, and a recombinant PR8, encephalomyocarditis virus (EMCV), and SARS-CoV-2 (SARS2). The film was irradiated with either UVA radiation (352 nm, 1.5 mW cm−2; although only 0.25 mW cm−2 for SARS2) or with light from a cool white fluorescent lamp (UVA irradiance: 365 nm, 0.047 mW cm−2). In all cases the films exhibited an average virus inactivation rate of >1.5log/h. In the case of SARS2, the rates were > 2log/h, with the rate determined using a dedicated, low intensity UVA source (0.25 mW cm−2) only 1.3 x's faster than that for a cool white lamp (UVA irradiance = 0.047 mW cm−2), which suggests that SARS2 is particularly prone to photocatalytic inactivation even under low UV irradiation conditions, such as found in a room lit with just white fluorescent tubes. This is the first example of a flexible, very thin, photocatalytic plastic film, produced by a scalable process (extrusion), for virus inactivation. The potential of such a film for use as a disposable, self-sterilising thin plastic material alternative to the common, non-photocatalytic, inert equivalent used currently for curtains, aprons and table coverings in healthcare is discussed briefly.

Expression stability of candidate RT-qPCR housekeeping genes in Spodoptera frugiperda (Lepidoptera: Noctuidae).

Reverse-transcription quantitative polymerase chain reaction (RT-qPCR) is commonly used to quantify gene expression. For normalization, the expression of each gene is compared with a reference "housekeeping" gene that is stably expressed under relevant stress. Unfortunately, there have been no reports on the stability of such reference genes under various treatments of the Spodoptera frugiperda. In this study, we used five tools (RefFinder, GeNorm, NormFinder, BestKeeper, and ΔCt methods) to evaluate the stability of 12 candidate reference genes (RPS18, β-tubulin, GAPDH, RPS7, RPS15, RPL7, RPL32, Actin-5C, EF1-α, EF1-γ, RPL27, and ACE) in different instars, tissues, and treatments (high and low temperature, UV-A, and emamectin benzoate). Several ribosomal proteins (RPS7, RPS15, RPL32, RPS18, and RPL7), GAPDH, Actin-5C, and β-tubulin, were relatively stable, suggesting that they are ideal housekeeping genes for various treatments. ACE was extremely unstable under various experimental treatments, rendering it unsuitable as an internal reference. This study identified the reference housekeeping genes stably expressed by S. frugiperda under different treatments, thus setting a foundation for further exploration of the physiological and biochemical mechanisms.

Epithelium-on Corneal Collagen Cross-Linking with Hypotonic Riboflavin Solution in Progressive Keratoconus.

IntroductionEpithelium-off cross-linking (epi-off CXL) has long been established as the gold standard treatment for progressive keratoconus. Several protocols for epithelium-on (epi-on) CXL have been proposed to help reduce post-operative pain and facilitate visual recovery, but there is no epi-on treatment approach that is currently approved in the United States. The hydrophilic and macromolecular characteristics of conventional epi-off riboflavin formulations may create clinical challenges for absorption through an intact epithelium. This study investigates the clinical efficacy of a dextran-free hypotonic riboflavin ophthalmic solution (Photrexa, Glaukos, Burlington, MA, USA), approved for epi-off CXL, in a novel epi-on CXL protocol.MethodsTwenty-five eyes of 17 patients were treated in this prospective, single-arm study using a hypotonic riboflavin formulation without dextran and low irradiance UVA (3mW/cm2) for epi-on CXL. Visual acuity, as well as refractive and keratometry outcomes, were observed over 12 months.ResultsAt 12 months, Kmax was stable with no clinically or statistically significant change from a mean pre-op of 55.4D to 55.9D (p=0.13). Uncorrected and best corrected logMAR visual acuity significantly improved from 0.77 to 0.62 and from 0.17 to 0.12, respectively. There were no significant adverse safety events.ConclusionPatients who underwent epi-on CXL with dextran-free hypotonic riboflavin demonstrated improvements in uncorrected and best corrected visual acuity with stable keratometry at 12 months post-operatively. The efficacy is consistent with other epi-on studies to date but remains lower than standard epi-off CXL. New technologies, including supplemental oxygen and transepithelial riboflavin ophthalmic solutions, are currently under clinical evaluation and may offer a path forward for epi-on CXL in the USA.

Downregulation of dihydrolipoyl dehydrogenase by UVA suppresses melanoma progression via triggering oxidative stress and altering energy metabolism

Melanoma, the most severe form of skin cancer, has poor prognosis and is resistant to chemotherapy. Targeting cancer metabolism is a promising approach in cancer therapeutics. Dihydrolipoyl dehydrogenase (DLD) is a mitochondrial enzyme with diaphorase activity. Here we report a pivotal role of DLD in melanoma cell progression and proliferation. Suppression DLD expression by low intensity UVA (125 mJ/cm2) increased intracellular ROS production and decreased mitochondrial membrane potential thereby inducing autophagy cell death which were confirmed by increased LC3BII and decreased p62 expression in melanoma cells. Knockdown of DLD in melanoma cells also showed similar results. More so, suppression of DLD significantly inhibits in vivo melanoma growth and tumor proliferation. In addition, suppression of DLD increased the NAD+/NADH ratio in melanoma cells and also inhibits TCA cycle related metabolites. DLD downregulation markedly increased α-ketoglutarate and decreased succinic acid suggesting that DLD suppression may have decreased TCA cycle downstream metabolites, resulting in the alteration of mitochondrial energy metabolism Thus the downregulation of DLD induced autophagic cell death in melanoma cells and inhibits in vivo tumor growth and proliferation by increasing ROS production and altering energy metabolism. Our findings suggest that DLD plays a pivotal role in melanoma progression and proliferation.

Low UVA intensity during cultivation improves the lettuce shelf-life, an effect that is not sustained at higher intensity

• The cultivation UVA level affects lettuce quality during shelf-life. • Low UVA intensity postpones the decrease of the primary energy reserves. • Low UVA intensity delays the decline of chlorophyll content, and decreases PPO activity. • Low UVA intensity reduces the ROS levels, owing to enhanced antioxidant activity. • The high UVA intensity mostly behaves comparably to the control. Sunlight includes UVA (320–400 nm). Since it is irrelevant for driving photosynthesis, less recognition is given to its usefulness in indoor cultivation. We examined how the cultivation under different UVA levels (0, 10 and 40 μmol m −2 s −1 ) affects the lettuce postharvest quality by evaluating the temporal dynamics of several underlying aspects, including weight loss, chlorophyll fluorescence, protein content, primary energy reserves (starch, sugars), pigments (chlorophyll, carotenoids), the activity of enzymes related to enzymatic browning [phenylalanine ammonia lyase, polyphenol oxidase (PPO)], the activity of antioxidant machinery enzymes (superoxide dismutase, catalase), the accumulation of non-enzymatic antioxidants (polyphenols, ascorbic acid) and the accumulation of reactive oxygen species (ROS; H 2 O 2 , O 2 − ). Evaluations were conducted (5 d intervals) on dark-stored excised leaves for 15 d (16 ℃, 70 % relative air humidity). Control samples gradually underwent a decrease in both primary energy reserves and protein content. They also suffered from color degradation owing to both a decrease in chlorophyll content and an enhanced PPO activity. Increased electrolyte leakage was also observed as a result of enhanced ROS levels. The low UVA level clearly improved all quality parameters, whereas the application of high UVA intensity caused limited effects in comparison to the control. In the former case, ROS accumulation was counteracted by an enhanced stimulation of the non-enzymatic and enzymatic antioxidant machinery. Overall, the results show that the promotive effect of UVA during cultivation on lettuce nutritional quality and shelf-life is strongly intensity-dependent and is mediated by diverse processes.

CaproGlu: Multifunctional tissue adhesive platform

Driven by the clinical need for a strong tissue adhesive with elastomeric material properties, a departure from legacy crosslinking chemistries was sought as a multipurpose platform for tissue mending. A fresh approach to bonding wet substrates has yielded a synthetic biomaterial that overcomes the drawbacks of free-radical and nature-inspired bioadhesives. A food-grade liquid polycaprolactone grafted with carbene precursors yields CaproGlu. The first-of-its-kind low-viscosity prepolymer is VOC-free and requires no photoinitiators. Grafted diazirine end-groups form carbene diradicals upon low energy UVA (365 nm) activation that immediately crosslink tissue surfaces; no pre-heating or animal-derived components are required. The hydrophobic polymeric environment enables metastable functional groups not possible in formulations requiring solvents or water. Activated diazirine within CaproGlu is uniquely capable of crosslinking all amino acids, even on wet tissue substrates. CaproGlu undergoes rapid liquid-to-biorubber transition within seconds of UVA exposure–features not found in any other bioadhesive. The exceptional shelf stability of CaproGlu allows gamma sterilization with no change in material properties. CaproGlu wet adhesiveness is challenged against current unmet clinical needs: anastomosis of spliced blood vessels, anesthetic muscle patches, and human platelet-mediating coatings. The versatility of CaproGlu enables both organic and inorganic composites for future bioadhesive platforms.

Effect of UVA radiation on the Nrf2 signalling pathway in human skin cells

The harmful effects of low energy UVA photons (315–400 nm) are associated with the massive production of reactive oxygen species resulting in oxidative stress. In response to oxidative damage, NF-E2-related factor 2 (Nrf2) is translocated to the nucleus and drives the expression of detoxication and antioxidant enzymes. UVA's effect on Nrf2 has been quite well characterised in dermal fibroblasts. However, there is a dearth of such information for keratinocytes. This study aimed to evaluate and compare the effect of UVA radiation on the Nrf2 pathway and oxidative stress related proteins in primary human dermal fibroblasts (NHDF), epidermal keratinocytes (NHEK) and human keratinocyte cell line HaCaT. NHDF were exposed to doses of 2.5–7.5 J/cm2, NHEK and HaCaT to 10–20 J/cm2 using a solar simulator. Effects on Nrf2 translocation were evaluated after 1, 3 and 6 h and Nrf2-controlled proteins (heme oxygenase 1 (HO-1), NAD(P)H:quinone oxidoreductase 1 (NQO1), glutathione reductase (GSR), glutathione-S-transferase (GST), interleukine-6 (IL-6), and matrix metalloproteinases (MMP-1, MMP-2)) after 3, 6 and 24 h. The results showed the fastest Nrf2 translocation was in UVA-irradiated HaCaT (1 h), persisting until the subsequent time interval (3 h), while in primary keratinocytes the effect of radiation was minimal. In NHDF, UVA-stimulated Nrf2 translocation was conspicuous 3 h after UVA treatment. In NHDF, most of the studied proteins (NQO1, HO-1, GSR, GSTM1 and MMP-1) showed the highest level 24 h after UVA exposure, except for MMP-2 and IL-6 which had their highest level at a shorter time incubation interval (3 h). In NHEK, NQO1, HO-1 and GST were increased 6 h after UVA exposure, GSR and MMP-2 level was slightly below or above the control level, and MMP-1 and IL-6 increased at shorter time intervals. When comparing NHEK and HaCaT, these cells displayed contrary responses in most of the Nrf2-controlled proteins. Thus, primary keratinocytes cannot be replaced with HaCaT when studying cell signalling such as the Nrf2 driven pathway and Nrf2-controlled proteins.

Urea–hydroxyapatite nanohybrid as an efficient nutrient source in Camellia sinensis (L.) Kuntze (tea)

Slow-release fertilizers based on nanomaterials have recently proven promise in increasing nitrogen use efficiency by plants and reduction in environmental hazards. We have previously reported the synthesis of an efficient and novel plant nutrient formulation based on urea–hydroxyapatite (HA) nanohybrid and its efficacy at small scale field trials conducted using rice as the model crop. This work focuses on a study of the effect of urea–HA nanohybrid fertilizer on the yield and quality of tea in farmer’s fields selected from three climatic zones (Low Country, Mid Country, and UVA regions) in Sri Lanka for a period of three years. Experiments were carried out using treatments with half and full amounts of nitrogen recommendations to the tea plant, supplied through both conventional urea and nanohybrids at two and four splits per annum. Annual N requirement supplied through nanohybrids in Low Country and Uva showed a yield increment of 10–17% and 14–16%, respectively, compared with conventional recommendation. Nanohybrid fertilizer also allowed to reduce the number of fertilizer applications and the amount used by 50% resulting in matching yields to the conventional fertilizer applications. However, only a minute yield increase of 2–3% was observed in mid Country. Yield component analysis carried out in the Uva region was evident for increased tea yield obtained by application of slow-release nanofertilizer. Moreover, application of slow-release fertilizer significantly increased soil P, leaf N, and P concentration in Low Country tea yields. A positive effect of HA–urea nanohybrids was more pronounced during unfavorable climatic conditions.

Pathogenesis of Photoaging in Human Dermal Fibroblasts

Pathogenesis of Photoaging in Human Dermal Fibroblasts

Photocatalytic biocidal effect of copper doped TiO2 nanotube coated surfaces under laminar flow, illuminated with UVA light on Legionella pneumophila.

Legionella pneumophila can cause a potentially fatal form of humane pneumonia (Legionnaires’ disease), which is most problematic in immunocompromised and in elderly people. Legionella species is present at low concentrations in soil, natural and artificial aquatic systems and is therefore constantly entering man-made water systems. The environment temperature for it’s ideal growth range is between 32 and 42°C, thus hot water pipes represent ideal environment for spread of Legionella. The bacteria are dormant below 20°C and do not survive above 60°C. The primary method used to control the risk from Legionella is therefore water temperature control. There are several other effective treatments to prevent growth of Legionella in water systems, however current disinfection methods can be applied only intermittently thus allowing Legionella to grow in between treatments. Here we present an alternative disinfection method based on antibacterial coatings with Cu-TiO2 nanotubes deposited on preformed surfaces. In the experiment the microbiocidal efficiency of submicron coatings on polystyrene to the bacterium of the genus Legionella pneumophila with a potential use in a water supply system was tested. The treatment thus constantly prevents growth of Legionella pneumophila in presence of water at room temperature. Here we show that 24-hour illumination with low power UVA light source (15 W/m2 UVA illumination) of copper doped TiO2 nanotube coated surfaces is effective in preventing growth of Legionella pneumophila. Microbiocidal effects of Cu-TiO2 nanotube coatings were dependent on the flow of the medium and the intensity of UV-A light. It was determined that tested submicron coatings have microbiocidal effects specially in a non-flow or low-flow conditions, as in higher flow rates, probably to a greater possibility of Legionella pneumophila sedimentation on the coated polystyrene surfaces, meanwhile no significant differences among bacteria reduction was noted regarding to non or low flow of medium.

New versatile bimolecular photoinitiating systems based on amino-m-terphenyl derivatives for cationic, free-radical and thiol–ene photopolymerization under low intensity UV-A and visible light sources

The performance of a series of 2-amino-4,6-diphenyl-benzene-1,3-dicarbonitrile derivatives as visible light sensitizers for diphenyliodonium salt for enabling photopolymerization at different irradiation wavelengths was studied.

Optimal sunscreen use allows vitamin D synthesis

Vitamin D, vital for bone health, is produced by the skin in response to ultraviolet radiation (UVR) from sunlight. However, as well as being the main source of vitamin D, UVR is a major cause of skin cancer. This has led to questions about how to prevent low levels of vitamin D whilst limiting the risk of skin cancer. This study, led by researchers from King's College London, found that use of sunscreen did not prevent most people from getting enough vitamin D whilst on a week‐long holiday to an area with a very high UV index. Whilst on holiday, 20 people received a broad‐spectrum sunscreen with a Sun Protection Factor (SPF) of 15, offering UVB protection and high UVA protection. Another 20 received a non‐broad‐spectrum sunscreen, also SPF 15 but with low UVA protection. These two groups were told how to use their sunscreens correctly to achieve the labelled SPF. In contrast, 22 people used their own sunscreen with no instructions on application, and 17 people formed a control group who remained in Poland. Blood samples were taken from participants 24 hours before and 24 to 48 hours after the holiday to check vitamin D levels. The first two groups saw a highly significant improvement in vitamin D levels. The group that used their own sunscreens also had significant vitamin D synthesis, but all had sunburn. During the same period, the control group had a slight decline in vitamin D.

Photorheology of bioadhesive dendrimer polycaprolactone composites

Toxicity, low adhesion strength, and complexity of application are the major challenges that prevent utilization of synthetic surgical adhesives. To address this challenge, a platform of fully synthetic UVA curing bioadhesive is evaluated on the binary composites consisting of polyamidoamine (PAMAM) grafted with aryl-diazirine (PAMAM-g-diazirine, PDz) and multi-arm polycaprolactone triols (PCLT). PCLT is chosen as a bioresorbable polymer matrix that serves as a plasticizer for the viscous PDz. Upon low dose UVA light, grafted diazirine converts to reactive carbenes that crosslink by covalent insertion. Rheological investigation created G″ vs. G′ vector maps of the liquid-to-solid transition, allowing comparison of PDz/PCLT ratio, PCLT molar mass, and type of plasticizer. The vector maps reveal crosslinking kinetics are dependent on the PCLT concentration within the composite, while the molar mass of liquid PCLT does not affect the crosslinking kinetics. Liquid PDz/PCLT composite adheres to dry substrates as well as hydrated soft tissue mimics. Infrared spectroscopy provides an insight into the crosslinking mechanism where UVA-generated carbenes covalently insert into proximate polymer chains mainly on –O–H sites. Carbene-induced intermolecular locking transforms the material from liquid to elastomeric composite polymer matrix in less than 10 J per sq. cm of UVA exposure.

EBT3-based dosimeter in characterizing UVA–LEDs with lambertian radiation pattern

PurposeThis paper aims to propose an area under the curve model to represent ultraviolet (UV) exposure doses on EBT3 films (in mJ/cm2). The model was developed on a cross-section of the exposed films using visible absorbance method. Ultraviolet–A light emitting diodes (UVA–LEDs) with 20° and 60° half angle with distinctive peak emission wavelengths between 365 to 405 nm are used in this experiment. No similar experimental setup or findings have been reported thus far, though the various application of EBT3 for the measurement of solar UV (A + B) have been published since EBT3 is commercially available.Design/methodology/approachTwo sets of UVA–LEDs were used as the UV radiation source in the experiment. The first set contains of four 5 mm low power UVA–LEDs with the 20° half angle and peak emission wavelength at 365, 375, 385 and 400 nm. The second set contains of five surface mount high power UVA–LEDs with the 60° half angle and peak emission wavelength at 365, 375, 385, 305 and 400 nm. The illumination setup for the two sets of LEDs is different between each other to obtain sufficient dose distribution on the films for spectroscopy analysis. This is due to the different illumination angle and irradiance intensity by each set of LEDs.FindingsUV–LED with a peak emission of 365, 375 and 385 nm able to produce UV doses accurately measurable using EBT3 films, UVA–LEDs with peak emission at 395 nm and above produced much lower accuracy with R2. From both set of LEDs, it can be concluded that peak emission wavelength of UVA–LED does influence the discoloration of the films. Shorter wavelength (higher energy) of UVA–LEDs discolors EBT3 films much intense compared to longer wavelength for a given UV dose exposure.Originality/valueDespite various practical applicability and advantages of UV–LEDs, there are still no standard methods in measuring UV–LED radiation output. The proposed approach not only allows us to obtain the dose of UV–LED, where the sensitivity of measurement is wavelength (energy) depended but also allows us to visually observe the illumination pattern of invisible UV radiation through the application of EBT3 films.