UV-B Radiation Research Articles

Bacterial Cellulose as a UVB Filter to Protect the Skin Microbiota.

Certain aerobic bacteria produce bacterial cellulose (BC) to protect themselves from UV radiation. Inspired by this natural function, the UV-filtering capacity of wet BC film (BC) and dried BC (BC-Dried) is evaluated and it is concluded that both samples hardly filter UVA, but filter UVB to some extent, especially BC-Dried. Moreover, this filtering capacity does not diminish but significantly increases with time, with efficiencies in the 145-160 min time range equal to or greater than most UV filters of the market. This increase in efficiency is due to the fact that the BC structure is modified by prolonged exposure to UVB radiation. Specifically, UVB causes sintering of the cellulose fibers, making the structure denser and increasing its reflection and scattering of UVB radiation. Remarkably, this UVB filtering ability of BC allows it to protect key skin probiotics, Lactobacillus fermentum (L. fermentum) and Cutibacterium acnes (C. acnes), against UVB damage. While the protection of healthy skin microbiota is not currently a regulatory requirement for sunscreens with UV filters, it may become a key differentiator for future UV filters given the increasing evidence on the role of skin microbiota in health.

Multi-Omics Analysis Reveals the Molecular Mechanisms of the Glycolysis and TCA Cycle Pathways in Rhododendron chrysanthum Pall. under UV-B Stress

UV-B radiation is becoming a bigger threat to plants as a result of the ozone layer’s depletion. As an alpine plant, Rhododendron chrysanthum Pall. (R. chrysanthum) may grow regularly under UV-B radiation throughout its lengthy acclimatization period, although the mechanism of acclimatization is still poorly understood. The current investigation uncovered a number of adaptation strategies that R. chrysanthum has developed in reaction to UV-B rays. UV-B radiation impeded photosynthesis and damaged the photosystem, according to OJIP testing. Through transcriptomics and proteomics analyses, this study found that the differential proteins and differential genes of R. chrysanthum were significantly enriched in glycolysis and tricarboxylic acid (TCA) cycle pathways after UV-B treatment. The metabolomics results showed that a total of eight differential metabolites were detected in the glycolytic and TCA cycle pathways, and the changes in the expression of these metabolites reflected the final outcome of gene regulation in the glycolytic and TCA cycle pathways. The combined experimental results demonstrated that R. chrysanthum’s photosynthetic system was impacted by UV-B stress and, concurrently, the plant activated an adaptation mechanism in response to the stress. To maintain its energy supply for growth, R. chrysanthum adapts to UV-B stress by adjusting the expression of the relevant proteins, genes, and metabolites in the glycolytic and TCA cycling pathways. This study provides a new perspective for understanding the changes in the carbon metabolism of R. chrysanthum under UV-B stress and its mechanisms for UV-B resistance, and provides an important theoretical basis for the study of enhancing plant resistance to stress.

Calcium signaling regulates the accumulation of phenolic acids in response to UV-B stress in Rhododendron chrysanthum Pall.

This study, using multi-omics combined with physiologic assays, found that calcium-ion signaling can regulate phenolic acid accumulation in R. chrysanthum leaves in response to UV-B stress. UV-B stress is a severe abiotic stress capable of destroying cellular structures and affecting plant growth. Rhododendron chrysanthum Pall. (R. chrysanthum) is a plant that has been exposed to high levels of UV-B radiation for an extended period, leading to the development of adaptive responses to mitigate UV-B stress. As such, it serves as a valuable experimental material for studying plant resilience to UV-B stress. We utilized R. chrysanthum as the experimental material and subjected it to UV-B stress. We conducted a comprehensive analysis of the changes in R. chrysanthum under both control and UV-B stress conditions using multi-omic and physiologic assays. Our aim was to investigate the molecular mechanism underlying R. chrysanthum's resistance to UV-B stress, with a focus on calcium-ion signaling. UV-B stress was found to impact the photosynthesis of R. chrysanthum by decreasing the maximum photosynthetic efficiency of photosystem II, reducing Fm, and increasing F0. In addition, the composition of numerous phenolic acid compounds was significantly altered. Genes and proteins related to calcium signaling showed significant differences, with some proteins (CML, CPK1, CRK3, ATP2C, ERG3, CAR7) being modified by acetylation. The correlation between genes and proteins involved in calcium signaling and phenolic compounds suggested that calcium signaling may play a role in regulating the accumulation of phenolic compounds under UV-B stress to help R. chrysanthum adapt. This study examines the impact of calcium-ion signaling on the accumulation of phenolic acid compounds, offering insights for future research on the molecular mechanisms underlying plant resilience to UV-B stress.

Pilose Antler Protein Relieves UVB-Induced HaCaT Cells and Skin Damage.

Extended exposure to UVB (280-315 nm) radiation results in oxidative damage and inflammation of the skin. Previous research has demonstrated that pilose antler extracts have strong anti-inflammatory properties and possess antioxidant effects. This study aimed to elucidate the mechanism of pilose antler protein in repairing photodamage caused by UVB radiation in HaCaT cells and ICR mice. Pilose antler protein (PAP) was found to increase the expression of type I collagen and hyaluronic acid in HaCaT cells under UVB irradiation while also inhibiting reactive oxygen species (ROS) production and oxidative stress in vitro. In vivo, the topical application of pilose antler protein effectively attenuated UVB-induced skin damage in ICR mice by reducing interleukin-1β (IL-β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) and inhibiting skin inflammation while alleviating UVB-induced oxidative stress. It was shown that pilose antler protein repaired UVB-induced photodamage through the MAPK and TGF-β/Smad pathways.

Effects of UV-B and UV-C Spectrum Supplementation on the Antioxidant Properties and Photosynthetic Activity of Lettuce Cultivars.

Indoor farming systems enable plant production in precisely controlled environments. However, implementing stable growth conditions and the absence of stress stimulants can weaken plants' defense responses and limit the accumulation of bioactive, health-beneficial phytochemicals. A potential solution is the controlled application of stressors, such as supplemental ultraviolet (UV) light. To this end, we analyzed the efficiency of short-term pre-harvest supplementation of the red-green-blue (RGB, LED) spectrum with ultraviolet B (UV-B) or C (UV-C) light to boost phytochemical synthesis. Additionally, given the biological harm of UV radiation due to high-energy photons, we monitored plants' photosynthetic activity during treatment and their morphology as well as sensory attributes after the treatment. Our analyses showed that UV-B radiation did not negatively impact photosynthetic activity while significantly increasing the overall antioxidant potential of lettuce through enhanced levels of secondary metabolites (total phenolics, flavonoids, anthocyanins), carotenoids, and ascorbic acid. On the contrary, UV-C radiation-induced anthocyanin accumulation in the green leaf cultivar significantly harmed the photosynthetic apparatus and limited plant growth. Taken together, we showed that short-term UV-B light supplementation is an efficient method for lettuce biofortification with healthy phytochemicals, while UV-C treatment is not recommended due to the negative impact on the quality (morphology, sensory properties) of the obtained leafy products. These results are crucial for understanding the potential of UV light supplementation for producing functional plants.

KGF-2 ameliorates UVB-triggered skin photodamage in mice by attenuating DNA damage and inflammatory response and mitochondrial dysfunction.

Long-term exposure to UVB induces DNA damage, inflammatory response, mitochondrial dysfunction, and apoptosis in skin cells, thus causing skin photodamage. Research has demonstrated the noteworthy antioxidant, anti-inflammatory, DNA repair, and mitochondrial protective properties of keratinocyte growth factor-2 (KGF-2). To examine the impact of KGF-2 on UVB-triggered skin photodamage in mice, hair-removed mice were initially exposed under UVB radiation and subsequently treated with KGF-2 hydrogel and repeated for 6 days. On day 7, the assessment of histopathological alterations, inflammation, DNA damage, mitochondrial function, and apoptosis in mouse skin was assessed. It was found that KGF-2 could effectively relieve cutaneous photodamage symptoms and inhibit epidermal proliferation in mice. Meanwhile, KGF-2 was found to significantly reduce DNA damage, attenuate the inflammatory response, and inhibit the mitochondria-mediated intrinsic apoptotic pathway in the UVB-exposed mouse skin photodamage model. To summarize, our results indicated that KGF-2 reduces the severity of mouse skin photodamage caused by UVB rays by attenuating DNA damage and the inflammatory response, besides inhibiting the mitochondria-mediated intrinsic apoptosis pathway.

A non-bactericidal cathelicidin with antioxidant properties ameliorates UVB-induced mouse skin photoaging via intracellular ROS scavenging and Keap1/Nrf2 pathway activation

Cathelicidins, a category of critical host defense molecules in vertebrates, have been extensively studied for their bactericidal functions, but little is known about their non-bactericidal properties. Herein, a novel cathelicidin peptide (Atonp2) was identified from the plateau frog Nanorana ventripunctata. It did not exhibit bactericidal activity but showed significant therapeutic effects in chronic UVB radiation-induced mouse skin photoaging through inhibiting thickening, pyroptosis and inflammation in the epidermis, while inhibiting cellular senescence, collagen fibre breakage and type Ⅰ collagen reduction in the dermis. Further studies indicated that Atonp2 effectively scavenged UVB-induced intracellular ROS via tyrosines at positions 9 and 10, while activating the Keap1/Nrf2 pathway to protect epidermal keratinocytes against UVB radiation, which in turn indirectly reversed the senescence and collagen degradation of dermal fibroblasts, thereby ameliorating UVB-induced skin photoaging. As such, this study identified a non-bactericidal cathelicidin peptide with potent antioxidant functions, highlighting its potential to treat and prevent skin photoaging.

BvCGT1-mediated differential distribution of flavonoid C-glycosides contributes to plant's response to UV-B stress.

C-glycosides are a predominant class of flavonoids that demonstrate diverse medical properties and plant physiological functions. The chemical stability, structural diversity, and differential aboveground distribution of these compounds in plants make them ideal protectants. However, little is known about the transcriptional regulatory mechanisms that play these diverse roles in plant physiology. In this study, chard was selected from 69 families for its significantly different flavonoid C-glycosides distributions between the aboveground and underground parts to investigate the role and regulatory mechanism of flavonoid C-glycosides in plants. Our results indicate that flavonoid C-glycosides are affected by various stressors, especially UV-B. Through cloning and validation of key biosynthetic genes of flavonoid C-glycosides in chard (BvCGT1), we observed significant effects induced by UV-B radiation. This finding was further confirmed by resistance testing in BvCGT1 silenced chard lines and in Arabidopsis plants with BvCGT1 overexpression. Yeast one-hybrid and dual-luciferase assays were employed to determine the underlying regulatory mechanisms of BvCGT1 in withstanding UV-B stress. These results indicate a potential regulatory role of BvDof8 and BvDof13 in modulating flavonoid C-glycosides content, through their influence on BvCGT1. In conclusion, we have effectively demonstrated the regulation of BvCGT1 by BvDof8 and BvDof13, highlighting their crucial role in plant adaptation to UV-B radiation. Additionally, we have outlined a comprehensive transcriptional regulatory network involving BvDof8 and BvDof13 in response to UV-B radiation.

Effect of UVB radiation on morphological, physiological and biochemical changes in methylotrophs

Effect of UVB radiation on morphological, physiological and biochemical changes in methylotrophs

Eugenol-Based High-Strength and Toughness Shape Memory Poly(urethane thioether) Networks as Intrinsic UV-Shielding Devices.

Ultraviolet (UV) light poses a significant threat to human health. Here, we propose a click preparation strategy for creating biomass-based poly(urethane thioether) networks for UV-shielding goggles designed to potentially protect the eyes from UV damage. Eugenol-based diurethanes (EDUs) were synthesized first, and then cross-linked networks were prepared through thiol-ene photoclick chemistry. The obtained high-strength and toughness eugenol-based poly(urethane thioether) networks (EUTNs) show a Young's modulus of 2.6 GPa, a tensile strength of 85 MPa, and a fracture elongation of 2066%. Meanwhile, EUTNs show shape memory behaviors and good optical properties. The EUTN films exhibit transparency while effectively filtering out approximately 99% of UVB and UVC radiation without any UV absorbers added. UV goggles can be integrally fabricated with both lenses and frames made entirely of the same EUTN material. What is more, goggles can be recovered to their original thin film form when not in use.

NDRG2 Deficiency Exacerbates UVB-Induced Skin Inflammation and Oxidative Stress Damage.

UVB radiation induces inflammatory and oxidative stress responses, contributing to skin damage, yet the underlying mechanisms are not fully understood. N-Myc downstream-regulated gene 2 (NDRG2), an emerging stress-associated gene, remains unexplored in UVB-induced skin injury. In this study, we detected skin NDRG2 expression after UVB irradiation for the first time and further used Ndrg2 knockout mice to clarify the role of NDRG2 in UVB-induced skin injury. Three-month-old male Ndrg2+/+ and Ndrg2-/- mice (16-18g) were exposed to UVB to induce acute skin damage, and then dorsal skin samples were collected for subsequent analyses. UVB-induced skin damage was scored. Western Blot Analysis, immunofluorescence (IF) double labeling, and immunohistochemistry (IHC) were employed to assess NDRG2 expression and/or distribution. The concentrations of TNF-α, IL-6, IL-1β, MPO, MMP8, superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) were quantitatively assessed using enzyme-linked immunosorbent assay (ELISA). Hematoxylin and eosin (HE) staining were employed to determine pathological changes. RNA sequencing and analysis were performed to estimate transcript expression levels and analyze mRNA expression. DESeq2 software was employed to identify differentially expressed genes (DEGs). DEGs were visualized using volcanic and heat maps. Gene Ontology (GO) functions and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were analyzed to identify primary biological functions, metabolic pathways, or signal transduction pathways associated with DEGs. UVB-challenged Ndrg2-/- mice exhibited significantly exacerbated skin damage (erythema, edema, and erosion), neutrophil infiltration, and apoptosis compared to Ndrg2+/+ mice. Furthermore, UVB-challenged Ndrg2-/- mice displayed significantly elevated pro-inflammatory cytokines, myeloperoxidase (MPO), matrix metalloproteinase-8 (MMP8), and reduced antioxidant expression. RNA sequencing identified 1091 significantly differentially expressed genes enriched in inflammation, immune response, and oxidative stress pathways. In conclusion, the deficiency of Ndrg2 markedly exacerbated UVB-induced skin damage by promoting inflammatory responses and inhibiting antioxidant responses. This suggests that stabilizing NDRG2 expression holds promise as a therapeutic strategy for protecting against UVB-induced skin damage.

UV LED ageing of polymers for PV cell encapsulation

Encapsulation polymers in terrestrial solar modules degrade due to ultraviolet radiation from the sun. To assess a polymer’s durability under UV light, accelerated aging tests can be conducted. A new LEDs device allows us to investigate the effects of temperature, irradiation, and UV source spectrum on the photooxidation mechanism and kinetics of two polyethylene-based commercial encapsulants, differentiated by the presence or absence of UV absorbers. The photooxidation rate of the polymer matrix increases as the temperature and irradiance increase between 62 and 82 °C, and 12 and 28 W.m−2, respectively. In the last case, the photooxidation rate is not proportional to the number of photons. Finally, we observed different distributions of degradation products under UVB radiation at 305 nm compared to those under UVA radiation at 365 nm. UVB photons enable Norrish reactions that are not possible with UVA alone. Special care is needed to maintain a balance between UVA and UVB photons to ensure representative durability tests. With a few adjustments to their emission spectrum, UV LED devices appear to be good candidates for accelerated aging of encapsulation polymers.

NtMYB27 acts downstream of NtBES1 to modulate flavonoids accumulation in response to UV-B radiation in tobacco.

UV-B radiation can induce the accumulation of many secondary metabolites, including flavonoids, in plants to protect them from oxidative damage. BRI1-EMS-SUPPRESSOR1 (BES1) has been shown to mediate the biosynthesis of flavonoids in response to UV-B. However, the detailed mechanism by which it acts still needs to be further elucidated. Here, we revealed that UV-B significantly inhibited the transcription of multiple transcription factor genes in tobacco, including NtMYB27, which was subsequently shown to be a repressor of flavonoids synthesis in tobacco. We further demonstrated that NtBES1 directly binds to the E-box motifs present in the promoter of NtMYB27 to mediate its transcriptional repression upon UV-B exposure. The UV-B-repressed NtMYB27 could bind to the ACCT-containing element (ACE) in the promoters of Nt4CL and NtCHS and served as a modulator that promoted the biosynthesis of lignin and chlorogenic acid (CGA) but inhibited the accumulation of flavonoids in tobacco. The expression of NtMYB27 was also significantly repressed by heat stress, suggesting its putative roles in regulating heat-induced flavonoids accumulation. Taken together, our results revealed the role of NtBES1 and NtMYB27 in regulating the synthesis of flavonoids during the plant response to UV-B radiation in tobacco.

UV-B Stress-Triggered Amino Acid Reprogramming and ABA-Mediated Hormonal Crosstalk in Rhododendron chrysanthum Pall.

Increased UV-B radiation due to ozone depletion adversely affects plants. This study focused on the metabolite dynamics of Rhododendron chrysanthum Pall. (R. chrysanthum) and the role of ABA in mitigating UV-B stress. Chlorophyll fluorescence metrics indicated that both JA and ABA increased UV-B resistance; however, the effect of JA was not as strong as that of ABA. Metabolomic analysis using UPLC-MS/MS (ultra-performance liquid chromatography and tandem mass spectrometry) revealed significant fluctuations in metabolites under UV-B and ABA application. UV-B decreased amino acids and increased phenolics, suggesting antioxidant defense activation. ABA treatment upregulated lipids and phenolic acids, highlighting its protective role. Multivariate analysis showed distinct metabolic clusters and pathways responding to UV-B and ABA, which impacted amino acid metabolism and hormone signal transduction. Exogenous ABA negatively regulated the JA signaling pathway in UV-B-exposed R. chrysanthum, as shown by KEGG enrichment. This study deepens understanding of plant stress-tolerance mechanisms and has implications for enhancing plant stress tolerance through metabolic and hormonal interventions.

Exploring the Benefits of Yashada Bhasma (Zinc Oxide) in Sunscreen Formulations: Bridging Classical Wisdom with Scientific Validation

The utilization of minerals in cosmetic formulations has been a longstanding tradition, with Yashada Bhasma (zinc oxide) emerging as a prominent ingredient in modern sunscreen formulations due to its remarkable properties. This article provides a comprehensive examination of Yashada Bhasma historical significance, chemical composition, and therapeutic attributes as described in classical literature. The scientific analysis validates its efficacy as a physical barrier against UVA and UVB radiation, highlighting its photostability and compatibility with sensitive skin. Structural and chemical characterization techniques illuminate its nano-scale transformation during the purification process, enhancing its effectiveness. Comparative analyses with other sunscreen ingredients emphasize its superiority in terms of UV protection spectrum, skin compatibility, and regulatory approval. A market survey reveals the widespread incorporation of Yashada Bhasma into various Ayurvedic and herbal cosmetic products, reflecting its acceptance and popularity among consumers. Overall, this article bridges the gap between Classical wisdom and scientific validation, showcasing Yashada Bhasma as a versatile and effective component in sunscreen formulations, poised to meet the evolving needs of skincare and sun protection in contemporary times.

Penilumamide, a novel SIRT1 activator, protects UVB-induced photodamages in HaCaT cells

ABSTRACT Ultraviolet-B (UVB) radiation is a major physical factor that induces structural changes in human skin. The aim of this study was to determine whether the novel silent information regulator 1 (sirtuin 1 SIRT1) protein activator, penilumamide, exerted any protective effects against UVB-induced skin damage using human HaCaT keratinocytes as a model. Enzymatic assays were performed to determine the SIRT1-activating ability of penilumamide, which was compared with that of resveratrol, a potent natural product SIRT1 activator with antioxidant and anti-inflammatory properties. Penilumamide markedly activated SIRT1 enzyme activity compared to resveratrol. To further investigate the protective effect of penilumamide against UVB-induced cytotoxicity, HaCaT cells were pretreated with penilumamide (10 μM) for 24 hr followed by irradiation with UVB (40 mJ/cm2). UVB (40 mJ/cm2) irradiation significantly reduced cell viability in a time-dependent manner, whereas pretreatment with penilumamide blocked this effect. Further, penilumamide decreased the levels of intracellular reactive oxygen species (ROS) generated by UVB irradiation in HaCaT cells. Pretreatment with penilumamide also prevented UVB irradiation-induced changes in mitochondrial membrane potential (ΔΨ m). In addition, pretreatment with penilumamide significantly reduced the expression levels of pro-inflammatory cytokines, interleukin (IL)-6, IL-8, and IL-10 and phosphorylation of nuclear factor-kB (NF-kB). These results indicate that penilumamide protects HaCaT cells from UVB-induced inflammation. Taken together data demonstrate that penilumamide exerted protective effects against UVB-induced ROS generation in HaCaT cells. Therefore, penilumamide may be considered to be used as a new SIRT1 activator to protect human keratinocyte against UVB-induced damage.

Loss of Lkb1 cooperates with BrafV600E and ultraviolet radiation, increasing melanoma multiplicity and neural-like dedifferentiation.

The mechanisms that work alongside BRAFV600E oncogene in melanoma development, in addition to ultraviolet (UV) radiation (UVR), are of great interest. Analysis of human melanoma tumors [data from The Cancer Genome Atlas (TCGA)] revealed that 50% or more of the samples expressed no or low amounts of serine/threonine protein kinase STK11 (also known as LKB1) protein. Here, we report that, in a mouse model, concomitant neonatal BrafV600E activation and Lkb1 tumor suppressor ablation in melanocytes led to full melanoma development. A single postnatal dose of UVB radiation had no effect on melanoma onset in Lkb1-depleted mice compared with BrafV600E-irradiated mice, but increased tumor multiplicity. In concordance with these findings and previous reports, Lkb1-null irradiated mice exhibited deficient DNA damage repair (DDR). Histologically, tumors lacking Lkb1 were enriched in neural-like tumor morphology. Genetic profiling and gene set enrichment analyses of tumor sample mutated genes indicated that loss of Lkb1 promoted the selection of altered genes associated with neural differentiation processes. Thus, these results suggest that the loss of Lkb1 cooperates with BrafV600E and UVR, impairing the DDR and increasing melanoma multiplicity and neural-like dedifferentiation.

The Effect of UV-A / UV-B Radiation on Quality Changes of Harvested Curly Lettuce During the Storage

This study investigated the effects of UV-A and UV-B radiation on curly lettuce quality. Results focused on colour, total phenolic content, antioxidant activity, and ascorbic acid. The findings revealed that the highest phenolic content (46.1 mg GAE/100 g FL) had been observed in lettuce samples treated with high dose UV-B on the 7th day. The lowest phenolic content (13.7 mg GAE/100 g FL) was recorded in those treated with low dose UV-B on the same day of storage. Data showed an increase of 29.7% in antioxidant activity and 53.7% in total phenolic content after 7 days of storage in samples treated with high dose UV-B. High dose UV-A radiation was found to be the most effective in maintaining and enhancing the ascorbic acid content of the lettuce. UV applications did not cause yellowing in the stored lettuce leaves. Further research on different doses and optimization is recommended.

Enhanced Catalytic Synthesis of Flavonoid by UV-B Radiation in Artemisia argyi

Enzymatic synthesis of specific active substances is an important foundation for biological adaptations to various stresses. In this study, we investigated the metabolic response of the medicinal herb Artemisia argyi to UV-B radiation through transcriptome and metabolome analysis. In all tested samples, there were 544 shared differentially expressed genes, most of which were linked to the metabolism of flavonoids and fatty acids. A total of 283 differential metabolites were identified and classified into 10 categories, with flavonoids being the largest category. Through an integrated analysis of genes and metabolites involved in flavonoid biosynthesis, flavonoids were predicted to be critical for the adaptation of A. argyi to UV radiation. The increased plant hormones methyl jasmonate and salicylic acid were considered as key regulatory approaches for catalyzing the large-scale synthesis of flavonoids. We explored this by investigating the flavonoid production of A. argyi grown at different altitudes. It showed that total flavonoid content of A. argyi planted in high-altitude areas was 45% higher than that in low-altitude areas. These findings not only deepen our understanding of flavonoid anabolism and its regulation but also provide a reliable strategy for improving flavonoid content in the genus Artemisia.

Data Processing for Predicting DNA Damaging Properties of Complex UV Sources.

A growing number of experimental evidence emphasizes that photobiological phenomena are not always the sum of the effect of individual wavelengths present in the emission spectrum of light sources. Unfortunately, tools are missing to identify such non-additive effects and predict effects of various exposure conditions. In the present work, we addressed these points for the formation of pyrimidine dimers in DNA upon co-exposure to UVC, UVB and UVA radiation. We first applied a combination index approach to determine whether mixtures of theses UV ranges exhibited additive, inhibitory or synergistic effects on the formation of cyclobutane pyrimidine dimers, (6-4) photoproducts and Dewar valence isomers. A predictive approach based on an experimental design strategy was then used to quantify the contribution of each wavelength range to the formation of DNA photoproducts. The obtained models allowed us to accurately predict the level of pyrimidine dimers in DNA irradiated under different conditions. The data were found to be more accurate than those obtained with the simple additive approach underlying the use of action spectra. Experimental design thus appears as an attractive concept that could be widely applied in photobiology even for cellular experiments.