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Our exposure to blue light from artificial sources such as indoor lights (mainly light-emitting diodes [LEDs]) and electronic devices (e.g., smartphones, computer monitors, and television screens), has increased in recent years, particularly during the recent coronavirus disease 2019 lockdown. This radiation has been associated to skin damage across its potential in generating reactive oxygen species in both the epidermis and the dermis, skin water imbalances and of potential activating melanin production. These circumstances make it important to determine whether current blue light exposure levels under artificial illumination and electronic devices exposure can cause the previously indicated disorders as compared to solar UV and visible radiation in a typical summer day. Blue light accounted for 25% of the sun's rays, approximately 30% of radiation emitted by electronic devices, and approximately from 6% to 40% of that emitted by indoor lights. The reference equations showed that the sun was the main source of effective irradiance for immediate and persistent pigmentation as well as for potential oxidative stress in our skin. Effective blue light exposure to artificial devices is significantly lower than the solar contribution. However, its contribution must be considered as accumulative dose effect, and especially in people with hypersensitivity promoting skin hyperpigmentation.

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One of the key aspects of photodynamic therapy is the light source that is used to irradiate the lesion to be treated. The devices used must ensure that their emission spectrum matches the absorption spectrum of the photosensitizer, so that treatment radiation is delivered only on the target area, without irradiating healthy tissue at superficial or deep levels. Irradiance values must be adequate in order to avoid thermal damage, exceed the oxygen replenishment rate and avoid long treatment times. Furthermore, the device should be user-friendly, inexpensive, and able to be adapted to different photosensitizers. We have developed an easy-to-use and highly customizable device based on LED technology. Its innovative geometric design allows radiation to be delivered to a small treatment surface, since the LEDs are arranged in three arms, the configuration of which directs their radiation on the treatment point. Different high-power color LEDs are disposed on the arms, and can be independently selected based on the most effective wavelengths for exciting the different photodynamic therapy photosensitizers. We have tested the prototype in 5 different patients (1 actinic keratose, 1 actinic cheilitis, 1 superficial basal cell carcinoma and 2 Bowen's disease) and after 1-2 sessions of total cumulative dose of 25-50 J / cm2, 100% clearance of lesions were obtained. Our device can be used by any professional in the field, whether for medical or research purposes. It facilitates the development of treatment protocols and trials with different photosensitizers.

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In the last decades, lighting installations in plant tissue culture have generally been renewed or designed based on LED technology. Thanks to this, many different light quality advances are available but, with their massive implementation, the same issue is occurring as in the 1960s with the appearance of the Grolux (Sylvania) fluorescent tubes: there is a lack of a methodological standardization of lighting. This review analyzes the main parameters and variables that must be taken into account in the design of LED-based systems, and how these need to be described and quantified in order to homogenize and standardize the experimental conditions to obtain reproducible and comparable results and conclusions. We have designed an experimental system in which the values of the physical environment and microenvironment conditions and the behavior of plant tissue cultures maintained in cabins illuminated with two lighting designs can be compared. Grolux tubes are compared with a combination of monochromatic LED lamps calibrated to provide a spectral emission, and light irradiance values similar to those generated by the previous discharge lamps, achieving in both cases wide uniformity of radiation conditions on the shelves of the culture cabins. This study can help to understand whether it is possible to use LEDs as one standard lighting source in plant tissue culture without affecting the development of the cultures maintained with the previously regulated protocols in the different laboratories. Finally, the results presented from this caparison indicate how temperature is one of the main factors that is affected by the chosen light source.

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Photodynamic therapy is taking importance as a nonintrusive treatment for nail onychomycosis. Knowledge of true transmittance values across nails could lead to qualitative and quantitative improvements in light-based treatments. We have characterized the spectral transmittance of healthy and fungally infected human fingernails and toenails according to nail thickness, and we propose a surface transmittance model for the small-scale optimization of light-based treatments. Transmittance of fingernails and toenails was analyzed by means of spectroradiometric measurements under solar-simulated visible light radiation (400 nm to 750 nm). The nail thickness was measured by means of microscope measurement. Transmittance was highest at longer wavelengths and decreased gradually as the wavelengths became shorter but with a significant nail transmittance of around 20% in the blue region of the spectrum. In the case of nails affected by onychomycosis, transmittance fell to under 10% because of the thickness of the nails, with no changes in spectral characteristics of transmitted light. Nail thickness is the main variable controlling exponentially light transmission in the visible spectrum and not only red radiation is effective for nail onychomycosis PDT. Blue light, the spectral band more effective for PPIX absorption is also effectively transmitted.

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