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Melanin is a chromophore that exists in the human epidermal layer of skin responsible for protection from harmful UV radiation. When melanocytes are stimulated by solar radiation, melanin is produced. [7] Melanin is one of the major absorbers of light in some biological tissue (although its contribution is smaller than other components).
Micrograph of paper autofluorescing under ultraviolet illumination. The individual fibres in this sample are around 10 μm in diameter.. Autofluorescence is the natural fluorescence of biological structures such as mitochondria and lysosomes, in contrast to fluorescence originating from artificially added fluorescent markers (fluorophores).
Usually the setup of a fluorescence assay involves a light source, which may emit many different wavelengths of light. In general, a single wavelength is required for proper analysis, so, in order to selectively filter the light, it is passed through an excitation monochromator, and then that chosen wavelength is passed through the sample cell.
He named them "mitogenetic rays" because his experiments convinced him that they had a stimulating effect on cell division. [23] In the 1970s Fritz-Albert Popp and his research group at the University of Marburg showed that the spectral distribution of the emission fell over a wide range of wavelengths, from 200 to 750 nm. [24]
Blood levels of folate, a nutrient vital for fetal development, can be degraded by UV radiation, [59] raising concerns about sun exposure for pregnant women. [60] Lifespan and fertility can be adversely affected for individuals born during peaks of the 11-year solar cycle , possibly because of UV-related folate deficiency during gestation.
The most common treatment is with narrowband UVB, which has a wavelength of approximately 311–313 nanometers. Full body phototherapy can be delivered at a doctor's office or at home using a large high-power UVB booth. [3] Tanning beds, however, generate mostly UVA light, and only 4% to 10% of tanning-bed light is in the UVB spectrum.
Parameters of interest, besides the wavelength of measurement, are absorbance (A) or transmittance (%T) or reflectance (%R), and its change with time. [4] [5] A UV-Vis spectrophotometer is an analytical instrument that measures the amount of ultraviolet (UV) and visible light that is absorbed by a sample. It is a widely used technique in ...
In the laboratory, calcium fluoride is commonly used as a window material for both infrared and ultraviolet wavelengths, since it is transparent in these regions (about 150 to 9000 nm) and exhibits an extremely low change in refractive index with wavelength. Furthermore, the material is attacked by few reagents.