Photochemistry and Photobiology

Photobiomodulation uses red or NIR light to stimulate healing and regeneration in tissue. The primary chromophores are cytochrome c oxidase in mitochondria and light/heat-gated ion channels. Both mechanisms lead to generation of reactive oxygen species that can activate transcription factors and may act as an exercise mimetic.

Effective treatment delivery in photodynamic therapy (PDT) requires careful coordination of the light source (e.g. lasers, light-emitting diodes and lamps), photosensitizer and delivery device (e.g. optical fiber-based devices) appropriate to the target tissue (e.g. geometry of minimally accessible areas). Treatment light undergoes scattering and absorption based on the optical properties of the tissue, for example, most tissue scatters light, but highly pigmented areas will absorb light, especially at short wavelengths. We summarize the basic physics of light sources and describe methods for determining the dose delivered to the patient.

The penetration depth of direct (a, b) and diffuse (c, d) radiation into a multi-layered skin model is shown for the wavelength range of 200–1000 nm. Each line represents a remaining percentage of incident radiation at depth plotted over a scaled image of the skin model.

The COVID-19 pandemic has generated great interest in ultraviolet germicidal irradiation (UVGI) as a means to disinfect air and surfaces. The development of shorter-wavelength UV-C lamps, such as 222-nm lamps, has led to concerns about the UV-C generation of ozone. It is known that wavelengths below 240 nm more readily generate ozone. However, there is a great misunderstanding about the actual generation and dissipation of ozone molecules by UV-C lamps. An overview of the ozone generation of various UVC light sources is presented to give users a better understanding of risk and how to control ozone when employing UV-C lamps.

The availability of absorption and fluorescence data (with ε and Φ_f values) is essential for for diverse studies in photochemistry including informed molecular design of photofunctional molecules. Such spectra for 339 compounds (spanning the ultraviolet, visible, and near-infrared spectral regions) have been assembled (339 absorption, 213 fluorescence spectra) in a database that is rooted with >650 references to the original scientific literature. A small database of 31 solar spectra also is available. The databases are available for diverse photophysical and spectrometric calculations with PhotochemCAD or other programs.

Photobiomodulation uses red or NIR light to stimulate healing and regeneration in tissue. The primary chromophores are cytochrome c oxidase in mitochondria and light/heat-gated ion channels. Both mechanisms lead to generation of reactive oxygen species that can activate transcription factors and may act as an exercise mimetic.

Effective treatment delivery in photodynamic therapy (PDT) requires careful coordination of the light source (e.g. lasers, light-emitting diodes and lamps), photosensitizer and delivery device (e.g. optical fiber-based devices) appropriate to the target tissue (e.g. geometry of minimally accessible areas). Treatment light undergoes scattering and absorption based on the optical properties of the tissue, for example, most tissue scatters light, but highly pigmented areas will absorb light, especially at short wavelengths. We summarize the basic physics of light sources and describe methods for determining the dose delivered to the patient.

A chemical actinometer is a chemical system (fluid, gas and solid) that undergoes a light-induced reaction (at a certain wavelength, λ). This review explores different kinds of practical chemical actinometers over various wavelength ranges in the ultraviolet and visible spectrum.

The sun is a vital component of our daily lives, from food to personal health and well-being. Lack of sun exposure has detrimental effects on our health. Likewise, overexposure to sun leaves us with long-term negative effects which may ultimately be worse than those caused by the lack of sun exposure. Sunscreen agents have been used for many years. Over time, UV filters have changed in hopes of being more effective; unfortunately, this has come at the cost of posing a risk to the consumer’s health and environment thus raising the question, is it really worthwhile using sunscreen?