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In frequency (and thus energy), UV rays sit between the violet end of the visible spectrum and the X-ray range. The UV wavelength spectrum ranges from 399 nm to 10 nm and is divided into 3 sections: UVA, UVB, and UVC. UV is the lowest energy range energetic enough to ionize atoms, separating electrons from them, and thus causing chemical reactions.
UV classifications include UVA (320-400 nm), UVB (290-320 nm) and UVC (200-280 nm). UV-absorbing compounds are used not only in sunscreen, but also in other personal care products, such as lipstick, shampoo, hair spray, body wash, toilet soap, and insect repellent. [ 2 ]
These lamps emit ultraviolet light with two peaks in the UVC band at 253.7 nm and 185 nm due to the mercury within the lamp, as well as some visible light. From 85% to 90% of the UV produced by these lamps is at 253.7 nm, whereas only 5–10% is at 185 nm. [ 39 ]
A 13 in (330 mm) telescope and the 82 in (2,100 mm) telescope at McDonald Observatory were used to define the system. [1] [3] The filters that Johnson and Morgan used were Corning 9 863 for U and 3 384 for V. The B filter used a combination of Corning 5 030 and Schott GG 13.
In astronomy, a photometric system is a set of well-defined passbands (or optical filters), with a known sensitivity to incident radiation.The sensitivity usually depends on the optical system, detectors and filters used.
UVB light (< 315 nm) is filtered mostly by the cornea, and UVA light (315–400 nm) is filtered mostly by the lens. [20] The lens also yellows with age, attenuating transmission most strongly at the blue part of the spectrum. [20] This can cause xanthopsia as well as a slight truncation of the short-wave (blue) limit of the visible spectrum.
When the UV index is presented on a daily basis, it represents UV intensity around the sun's highest point in the day, called solar noon, halfway between sunrise and sunset. This typically occurs between 11:30 and 12:30, or between 12:30 and 13:30 in areas where daylight saving time is being observed.
far UV (or vacuum UV) (200–10 nm; abbrev. FUV or VUV) extreme UV (1–31 nm; abbrev. EUV or XUV). Only near UV is of interest for UV photography, for several reasons. Ordinary air is opaque to wavelengths below about 200 nm, and most transparent lens glass is opaque below about 180 nm. UV photographers subdivide the near UV into: Long wave UV ...